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RSS2014 Vol. 26, No. 08
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2014,
26: 081001.
doi: 10.11884/HPLPB201426.081001
Abstract:
kW-class all-fiber laser was designed by employing master oscillator power amplifier (MOPA) configuration. Power output and distribution, mode controlling by bending, thermal distribution of active fiber in cooling condition were numerically analyzed. The fiber laser based on our design was built up. In the experiment, 1060 W continuous laser was obtained with a total pumped power of 1436 W. The optical-optical conversion efficiency was 73.8% and the beam quality M2 was less than 1.6. We preliminarily discussed the difference between the experimental results and theoretical design.
kW-class all-fiber laser was designed by employing master oscillator power amplifier (MOPA) configuration. Power output and distribution, mode controlling by bending, thermal distribution of active fiber in cooling condition were numerically analyzed. The fiber laser based on our design was built up. In the experiment, 1060 W continuous laser was obtained with a total pumped power of 1436 W. The optical-optical conversion efficiency was 73.8% and the beam quality M2 was less than 1.6. We preliminarily discussed the difference between the experimental results and theoretical design.
2014,
26: 081002.
doi: 10.11884/HPLPB201426.081002
Abstract:
In order to achieve large-scale numerical simulation of chemical oxygen-iodine laser(COIL) flow, a three-dimensional COIL multiblock parallel simulation code is developed. In this code, the basic equations and numerical algorithms of VICON code are adopted, and the patch-based data structure and the parallel algorithm for multiblock structured mesh of JASMIN infrastructure are used. The simulation results demonstrate the accuracy and scalability of the parallel simulation code. In the simulation example with 4.5 million meshes in 2048 CPU cores, the speedup of the code is higher than 420.
In order to achieve large-scale numerical simulation of chemical oxygen-iodine laser(COIL) flow, a three-dimensional COIL multiblock parallel simulation code is developed. In this code, the basic equations and numerical algorithms of VICON code are adopted, and the patch-based data structure and the parallel algorithm for multiblock structured mesh of JASMIN infrastructure are used. The simulation results demonstrate the accuracy and scalability of the parallel simulation code. In the simulation example with 4.5 million meshes in 2048 CPU cores, the speedup of the code is higher than 420.
2014,
26: 081003.
doi: 10.11884/HPLPB201426.081003
Abstract:
Atmospheric coherence length is a very important parameter in the study of effect of atmospheric turbulence on the astronomical observation and laser propagation. Two methods of measurement of atmospheric coherence length using the Shack-Hartmann wavefront sensor are studied. One is differential image motion measure which measures the optical waves angle-of-arrival fluctuation of two subapertures. The other is to measure the wavefront distribution of stars, and the atmospheric coherence length is obtained by the residual variance of wavefront distribution. The experiment results show that the measurement results obtained by the two methods are consistent, and reliable data of atmospheric coherence length are obtained, so both methods can validate each other. The method measuring wavefront distribution and getting the current atmosphere information at the same time is achieved, and the analysis of the measurement results have reference value.
Atmospheric coherence length is a very important parameter in the study of effect of atmospheric turbulence on the astronomical observation and laser propagation. Two methods of measurement of atmospheric coherence length using the Shack-Hartmann wavefront sensor are studied. One is differential image motion measure which measures the optical waves angle-of-arrival fluctuation of two subapertures. The other is to measure the wavefront distribution of stars, and the atmospheric coherence length is obtained by the residual variance of wavefront distribution. The experiment results show that the measurement results obtained by the two methods are consistent, and reliable data of atmospheric coherence length are obtained, so both methods can validate each other. The method measuring wavefront distribution and getting the current atmosphere information at the same time is achieved, and the analysis of the measurement results have reference value.
2014,
26: 081004.
doi: 10.11884/HPLPB201426.081004
Abstract:
The laser pulse waveform real-time precision measurement technology based on time division multiplexing (TDM) was developed for all fiber multi-beam high repetition frequency laser system. According to the characteristic of the system, we designed a kind of 18 optical time division multiplexer and a kind of 12 optical time division multiplexer with different time delay. Also we experimentally demonstrated the technology in the system, the results show that the pulse duration, pulse energy and rise time could be accurately measured, and meanwhile the system working status could be inspected in real time.
The laser pulse waveform real-time precision measurement technology based on time division multiplexing (TDM) was developed for all fiber multi-beam high repetition frequency laser system. According to the characteristic of the system, we designed a kind of 18 optical time division multiplexer and a kind of 12 optical time division multiplexer with different time delay. Also we experimentally demonstrated the technology in the system, the results show that the pulse duration, pulse energy and rise time could be accurately measured, and meanwhile the system working status could be inspected in real time.
2014,
26: 081005.
doi: 10.11884/HPLPB201426.081005
Abstract:
The thermal response experiments of TA15 Ti alloy and LY12 Al alloy irradiated by CW laser in supersonic flow or natural convection conditions were done, temperature history curves and perforation time were obtained. The results show that the flow effect is cooling before the material is melted, it is denudation effect while the material is melting, it is helpful of accelerating the material ablation and perforation. The tangential air flow can have an effect on the temperature distribution of TA15 Ti alloy, but no effect on Al alloy.
The thermal response experiments of TA15 Ti alloy and LY12 Al alloy irradiated by CW laser in supersonic flow or natural convection conditions were done, temperature history curves and perforation time were obtained. The results show that the flow effect is cooling before the material is melted, it is denudation effect while the material is melting, it is helpful of accelerating the material ablation and perforation. The tangential air flow can have an effect on the temperature distribution of TA15 Ti alloy, but no effect on Al alloy.
2014,
26: 081006.
doi: 10.11884/HPLPB201426.081006
Abstract:
The infrared focal plane system cant provide well distributed gray of every temperature section and sufficient image details for targets with extreme temperature difference. To address this problem, an adaptive bilocal enhancement algorithm was proposed. This paper gives a detailed introduction about the adaptive bilocal enhancement algorithm from two aspects: spatial distribution and gray statistics characteristics. This algorithm adaptively divides the original image into several sub-images based on the spatial distribution of infrared image, then gets the local histogram statistics based on the local gray statistics characteristics, and do adaptive segment equalization on the histogram of every local space. At last, the enhanced images were mosaicked by linear interpolation algorithm. The practicability of this algorithm has been verified by a series of experiments on the infrared focal plane system. The effect was satisfactory and the imaging quality was improved significantly.
The infrared focal plane system cant provide well distributed gray of every temperature section and sufficient image details for targets with extreme temperature difference. To address this problem, an adaptive bilocal enhancement algorithm was proposed. This paper gives a detailed introduction about the adaptive bilocal enhancement algorithm from two aspects: spatial distribution and gray statistics characteristics. This algorithm adaptively divides the original image into several sub-images based on the spatial distribution of infrared image, then gets the local histogram statistics based on the local gray statistics characteristics, and do adaptive segment equalization on the histogram of every local space. At last, the enhanced images were mosaicked by linear interpolation algorithm. The practicability of this algorithm has been verified by a series of experiments on the infrared focal plane system. The effect was satisfactory and the imaging quality was improved significantly.
2014,
26: 081007.
doi: 10.11884/HPLPB201426.081007
Abstract:
Diffraction characteristic of transmitting volume Bragg grating is analyzed with classical coupled wave theory, and the design method of transmitting volume Bragg grating is built. The near-field filtering effect is simulated with modulated super-Gaussian beam. The softening factor, near-field modulation and near-field contrast are used to analyze the beam quality. The power spectral density is used to describe the evolution of spatial frequency. The results show that the spatial frequencies from 0.3 mm-1 to 2.0 mm-1 are clean out with the near-field filtering, but the filtering effect is limited by the beam diffraction sidelobes of transmitting volume Bragg grating.
Diffraction characteristic of transmitting volume Bragg grating is analyzed with classical coupled wave theory, and the design method of transmitting volume Bragg grating is built. The near-field filtering effect is simulated with modulated super-Gaussian beam. The softening factor, near-field modulation and near-field contrast are used to analyze the beam quality. The power spectral density is used to describe the evolution of spatial frequency. The results show that the spatial frequencies from 0.3 mm-1 to 2.0 mm-1 are clean out with the near-field filtering, but the filtering effect is limited by the beam diffraction sidelobes of transmitting volume Bragg grating.
2014,
26: 081008.
doi: 10.11884/HPLPB201426.081008
Abstract:
A potential of line and plane imaging velocity interferometer system for any reflector (VISAR) in hypervelocity impact study was exampled by velocity filed measurement of laser driven flyer. A streak camera and a framing camera were simultaneously used to captures the comb fringe, which allows to measure the velocity histories of different points along line segments and to measure velocity field across a plane at several times. A spatial resolution better than 10 m and a velocity resolution of 15 m/s were realized. The technique was employed to measure a temporal-spatial velocity field of Al foils flyer driven by a pulse laser, and to reveal the continuous evolution of flyers. These results demonstrate that the line and plane imaging VISAR can yield reliable experimental data for theoretical study and mathematical simulation of laser driven flyer or hypervelocity impact.
A potential of line and plane imaging velocity interferometer system for any reflector (VISAR) in hypervelocity impact study was exampled by velocity filed measurement of laser driven flyer. A streak camera and a framing camera were simultaneously used to captures the comb fringe, which allows to measure the velocity histories of different points along line segments and to measure velocity field across a plane at several times. A spatial resolution better than 10 m and a velocity resolution of 15 m/s were realized. The technique was employed to measure a temporal-spatial velocity field of Al foils flyer driven by a pulse laser, and to reveal the continuous evolution of flyers. These results demonstrate that the line and plane imaging VISAR can yield reliable experimental data for theoretical study and mathematical simulation of laser driven flyer or hypervelocity impact.
2014,
26: 081009.
doi: 10.11884/HPLPB201426.081009
Abstract:
This paper introduces a general technology of high precision synchronizing system for large-scale laser facility. This technology realized the generation of magnitude number of multiple frequency synchronizing signals by adopting clock and data recover and optic fiber transmission. Time interval jitter of the picosecond precise signals was less than 100 ps (peak to peak jitter) and 10 ps (RMS jitter). This technology was used on research of high precision synchronizing system for large-scale laser facilities and good result was acquired. This technology can help building medical instruments and be used in related experimental tests.
This paper introduces a general technology of high precision synchronizing system for large-scale laser facility. This technology realized the generation of magnitude number of multiple frequency synchronizing signals by adopting clock and data recover and optic fiber transmission. Time interval jitter of the picosecond precise signals was less than 100 ps (peak to peak jitter) and 10 ps (RMS jitter). This technology was used on research of high precision synchronizing system for large-scale laser facilities and good result was acquired. This technology can help building medical instruments and be used in related experimental tests.
2014,
26: 081010.
doi: 10.11884/HPLPB201426.081010
Abstract:
The coherent-beam-combining device and the requirements for optical-path adjustment were analyzed. Detecting the coherence of combined beams using the shearing interferometer was proposed. According to the principle of shearing interferometer, the physical model was constructed. Taking two coherent rectangular beams rectangling as an example, numerical simulation was studied on the relationship between the errors and the fringes. This method was visual, simple and precise. The results show that the existence of phase piston can be tested by shearing interferometer. So shearing interferometer could be a new method of detecting phase errors for coherent beam combination.
The coherent-beam-combining device and the requirements for optical-path adjustment were analyzed. Detecting the coherence of combined beams using the shearing interferometer was proposed. According to the principle of shearing interferometer, the physical model was constructed. Taking two coherent rectangular beams rectangling as an example, numerical simulation was studied on the relationship between the errors and the fringes. This method was visual, simple and precise. The results show that the existence of phase piston can be tested by shearing interferometer. So shearing interferometer could be a new method of detecting phase errors for coherent beam combination.
2014,
26: 081011.
doi: 10.11884/HPLPB201426.081011
Abstract:
Based on the Ginzburg-Landau equation, the limitation of the B integral issue is studied via numerical simulation for 100 kHz fiber chirped pulse amplification system. The compressibility of the pulse with the B integral under the typical amplifier structure is analyzed. The B integral limitation for 1 ns stretched pulse and 1 ps compressed pulse is given to be around 40 rad. A multi-pulse scheme is proposed to suppress the B integral of each pulse and is verified by theoretical simulation.
Based on the Ginzburg-Landau equation, the limitation of the B integral issue is studied via numerical simulation for 100 kHz fiber chirped pulse amplification system. The compressibility of the pulse with the B integral under the typical amplifier structure is analyzed. The B integral limitation for 1 ns stretched pulse and 1 ps compressed pulse is given to be around 40 rad. A multi-pulse scheme is proposed to suppress the B integral of each pulse and is verified by theoretical simulation.
2014,
26: 081012.
doi: 10.11884/HPLPB201426.081012
Abstract:
In order to solve the engineering problem of signal-noise-ratio decreasing with smaller optical path length of miniaturized ring laser, we prepare a narrow band pass filter for suppressing the discharge glow of He-Ne Gas. The filters central wavelength is 633 nm, and is incident at angle of 45 from the air. The substrate of the filter is a long wave pass red glass with transiting wavelength of 550 m. We deposit a 19-layer filter with layer structure as {HL2HLHLHLH2LHLHLHLH2LH} on one side of the substrate, and a 4-layer non-quart-wave antireflection coating on the other, by method of ion sputtering and quartz crystal monitoring of layer thickness. We measure the transmittance curve of the deposited filter by Lambda950 spectrometer, and find a good fit to it by reverse engineering technique. When this filter is glued to the output mirror of ring laser, the counting signals amplitude nearly does not change while the noises amplitude decreases by 80%. It is showed that a fivefold improvement of signal-noise-ratio has been optically achieved by the filter, which decreases the burden and complexity of the following processing circuits and plays a significant role to miniaturized ring laser development.
In order to solve the engineering problem of signal-noise-ratio decreasing with smaller optical path length of miniaturized ring laser, we prepare a narrow band pass filter for suppressing the discharge glow of He-Ne Gas. The filters central wavelength is 633 nm, and is incident at angle of 45 from the air. The substrate of the filter is a long wave pass red glass with transiting wavelength of 550 m. We deposit a 19-layer filter with layer structure as {HL2HLHLHLH2LHLHLHLH2LH} on one side of the substrate, and a 4-layer non-quart-wave antireflection coating on the other, by method of ion sputtering and quartz crystal monitoring of layer thickness. We measure the transmittance curve of the deposited filter by Lambda950 spectrometer, and find a good fit to it by reverse engineering technique. When this filter is glued to the output mirror of ring laser, the counting signals amplitude nearly does not change while the noises amplitude decreases by 80%. It is showed that a fivefold improvement of signal-noise-ratio has been optically achieved by the filter, which decreases the burden and complexity of the following processing circuits and plays a significant role to miniaturized ring laser development.
2014,
26: 081013.
doi: 10.11884/HPLPB201426.081013
Abstract:
Improving the ejector efficiency is a key technique in the research of ejector-type pressure recovery system (PRS) of COIL, and the goal could be achieved using active cooling technique which would reduce the exhaust gas temperature. Based on the design parameters gained by theoretic and numerical calculations, a cooling equipment with finned tube heat exchanger is manufactured, which uses liquid nitrogen as refrigerant. Final experimental results show that the exhaust gas temperature could be reduce from 590 K to 160 K in the experiment lasting for 60 s, and the temperature un-uniformity could be controlled within 21 K at the exit section of the heat exchanger, and the total pressure loss of the heat exchanger is less than 100 Pa.
Improving the ejector efficiency is a key technique in the research of ejector-type pressure recovery system (PRS) of COIL, and the goal could be achieved using active cooling technique which would reduce the exhaust gas temperature. Based on the design parameters gained by theoretic and numerical calculations, a cooling equipment with finned tube heat exchanger is manufactured, which uses liquid nitrogen as refrigerant. Final experimental results show that the exhaust gas temperature could be reduce from 590 K to 160 K in the experiment lasting for 60 s, and the temperature un-uniformity could be controlled within 21 K at the exit section of the heat exchanger, and the total pressure loss of the heat exchanger is less than 100 Pa.
2014,
26: 081014.
doi: 10.11884/HPLPB201426.081014
Abstract:
A high repetition rate femtosecond laser was used to irradiate a europium complex film, and a self-organizing symmetrical structure-like droplet was successfully induced which we called micro-crown structure. In order to research the relationship between micro-crown formation and machining condition, we changed laser pulses, average power, and numerical aperture of microscope. We analyzed the experiment results theoretically by referring to laser molten pool model and droplets sputtering model. The micro-crown structure appeared in femtosecond laser irradiation region while the pulses reached a certain value. Irradiation region size change was caused by thermo-capillary forces and chemical-capillary forces in liquid area. The sputter change was due to rapid gas expansion in gaseity area caused by multiphoton absorption.
A high repetition rate femtosecond laser was used to irradiate a europium complex film, and a self-organizing symmetrical structure-like droplet was successfully induced which we called micro-crown structure. In order to research the relationship between micro-crown formation and machining condition, we changed laser pulses, average power, and numerical aperture of microscope. We analyzed the experiment results theoretically by referring to laser molten pool model and droplets sputtering model. The micro-crown structure appeared in femtosecond laser irradiation region while the pulses reached a certain value. Irradiation region size change was caused by thermo-capillary forces and chemical-capillary forces in liquid area. The sputter change was due to rapid gas expansion in gaseity area caused by multiphoton absorption.
2014,
26: 081015.
doi: 10.11884/HPLPB201426.081015
Abstract:
HfO2/ SiO2 high reflection(HR) films with conventional quarterwave design were deposited by electron beam evaporation on fused silica substrate for the wavelength 248 nm. Two kinds of protective layer were designed and prepared to resist laser induced damage. For one sample half wavelength thick SiO2 were deposited on conventional quarterwave (HL)11H films as a protective layer, for the other sample Al2O3/MgF2 coatings were deposited as protective layers. Laser induced damage were tested. Through changes of the damage morphology, causes of laser resistance improvement and problems still exist were analyzed.
HfO2/ SiO2 high reflection(HR) films with conventional quarterwave design were deposited by electron beam evaporation on fused silica substrate for the wavelength 248 nm. Two kinds of protective layer were designed and prepared to resist laser induced damage. For one sample half wavelength thick SiO2 were deposited on conventional quarterwave (HL)11H films as a protective layer, for the other sample Al2O3/MgF2 coatings were deposited as protective layers. Laser induced damage were tested. Through changes of the damage morphology, causes of laser resistance improvement and problems still exist were analyzed.
2014,
26: 081016.
doi: 10.11884/HPLPB201426.081016
Abstract:
The 0Cr18Ni9 stainless steel sheet was cut and drilled by a femtosecond laser, and the influence factors of machining accuracy of femtosecond laser ablation were studied. The morphology of stainless steel ablation zone and metallographic structure of cutting seam were examined by means of Nikon SMZ800 optical microscope and 4XC optical metallographic microscope. Based on the laser speckle on the surface of stainless steel observed by a coaxial CCD in the process of stainless steel ablation, the laser beam divergent propagation behavior was simulated using COMSOL Multiphysic numerical simulation software, and the beam divergence angle was calculated. Experimental and simulation results demonstrate that when the laser repetition rate is 5 kHz, the edge of cutting seam and hole are obviously blackened; metallographic phase shows that grain size significantly gets larger at cutting seam and heat affected zone cant be avoided in the femtosecond laser ablation process; metal-air hybrid plasma induced by ultra-high power density femtosecond laser makes the laser beam scatter along the direction of propagation in the process of machining, the divergence angle is between 6 to 10. The existence of heat affected zone and the behavior of the metal-air hybrid plasma are the main factors influencing the precision of femtosecond laser ablation.
The 0Cr18Ni9 stainless steel sheet was cut and drilled by a femtosecond laser, and the influence factors of machining accuracy of femtosecond laser ablation were studied. The morphology of stainless steel ablation zone and metallographic structure of cutting seam were examined by means of Nikon SMZ800 optical microscope and 4XC optical metallographic microscope. Based on the laser speckle on the surface of stainless steel observed by a coaxial CCD in the process of stainless steel ablation, the laser beam divergent propagation behavior was simulated using COMSOL Multiphysic numerical simulation software, and the beam divergence angle was calculated. Experimental and simulation results demonstrate that when the laser repetition rate is 5 kHz, the edge of cutting seam and hole are obviously blackened; metallographic phase shows that grain size significantly gets larger at cutting seam and heat affected zone cant be avoided in the femtosecond laser ablation process; metal-air hybrid plasma induced by ultra-high power density femtosecond laser makes the laser beam scatter along the direction of propagation in the process of machining, the divergence angle is between 6 to 10. The existence of heat affected zone and the behavior of the metal-air hybrid plasma are the main factors influencing the precision of femtosecond laser ablation.
2014,
26: 081017.
doi: 10.11884/HPLPB201426.081017
Abstract:
A spontaneous vibration Raman scattering(SVRS) system for the simultaneous measurement of the major species concentrations in kerosene combustion was presented. The accuracy of SVRS was analyzed by measuring the major species concentrations in the air. The fluorescence characteristic of kerosene induced by 355 nm laser was obtained and analyzed. Under different burning conditions, the kerosene combustion was diagnosed by SVRS, the Raman spectra of the major species (N2, O2, H2O,CO2) in lean kerosene combustion were obtained, and the major species concentrations during the combustion process was calculated.
A spontaneous vibration Raman scattering(SVRS) system for the simultaneous measurement of the major species concentrations in kerosene combustion was presented. The accuracy of SVRS was analyzed by measuring the major species concentrations in the air. The fluorescence characteristic of kerosene induced by 355 nm laser was obtained and analyzed. Under different burning conditions, the kerosene combustion was diagnosed by SVRS, the Raman spectra of the major species (N2, O2, H2O,CO2) in lean kerosene combustion were obtained, and the major species concentrations during the combustion process was calculated.
2014,
26: 081018.
doi: 10.11884/HPLPB201426.081018
Abstract:
Based on position and altitude information of target and platform, a target guiding model of motional platform is established using rotation matrix. By introducing data error of different levels, the influence of target and platform information on the accuracy of guiding data is simulated and analyzed. It is demonstrated that the data errors of platform longitude, latitude, and yaw have significant impacts on the accuracy of azimuth, the data errors of platform longitude, latitude, pitch and roll have significant impacts on the accuracy of elevation, the data errors of platform longitude and latitude have significant impacts on the accuracy of range.
Based on position and altitude information of target and platform, a target guiding model of motional platform is established using rotation matrix. By introducing data error of different levels, the influence of target and platform information on the accuracy of guiding data is simulated and analyzed. It is demonstrated that the data errors of platform longitude, latitude, and yaw have significant impacts on the accuracy of azimuth, the data errors of platform longitude, latitude, pitch and roll have significant impacts on the accuracy of elevation, the data errors of platform longitude and latitude have significant impacts on the accuracy of range.
2014,
26: 081019.
doi: 10.11884/HPLPB201426.081019
Abstract:
The diffraction character is redefined based on Fresnel number. This new definition is extended to focusing or diffusing optical path. The sign of the new diffraction character is defined for each optical element in a laser system. According to these definitions and extending, the effect of phase aberration on near-field modulation and the effect of linear diffraction on FM-to-AM are studied. The linear diffraction effect on high power laser facility can be evaluated by the combination of the new diffraction character and the energy fluence.
The diffraction character is redefined based on Fresnel number. This new definition is extended to focusing or diffusing optical path. The sign of the new diffraction character is defined for each optical element in a laser system. According to these definitions and extending, the effect of phase aberration on near-field modulation and the effect of linear diffraction on FM-to-AM are studied. The linear diffraction effect on high power laser facility can be evaluated by the combination of the new diffraction character and the energy fluence.
2014,
26: 081020.
doi: 10.11884/HPLPB201426.081020
Abstract:
We theoretically investigate the generation of square optical bottles, which are generated by a pair of symmetric Airy beams induced by a binary phase pattern. A regulable linear factor is introduced into the phase function to modulate flexibly the size of resulting optical bottle. Numerical simulations are performed and results show that a Gaussian beam can be shaped into a square optical bottle by a tunable binary cubic phase pattern. The linear factor can vary the size of zero or low intensity region of optical bottle. It is believed that the intriguing characteristic of square optical bottle can be applied in many applications such as optical tweezers, atom trapping and manipulating.
We theoretically investigate the generation of square optical bottles, which are generated by a pair of symmetric Airy beams induced by a binary phase pattern. A regulable linear factor is introduced into the phase function to modulate flexibly the size of resulting optical bottle. Numerical simulations are performed and results show that a Gaussian beam can be shaped into a square optical bottle by a tunable binary cubic phase pattern. The linear factor can vary the size of zero or low intensity region of optical bottle. It is believed that the intriguing characteristic of square optical bottle can be applied in many applications such as optical tweezers, atom trapping and manipulating.
2014,
26: 081021.
doi: 10.11884/HPLPB201426.081021
Abstract:
In order to systematically evaluate the characteristic parameters of far field speckle in the real atmosphere condition and analyze the influence of laser atmospheric propagation on the optoelectronic system, a monitoring method is presented using large aperture projection optics. The projection optics is made of low cost and large aperture Fresnel lens, which can project the irradiance distribution of far field speckle on the CCD detector. The receiving power and scintillation index on a certain aperture can be evaluated through CCD imaging process. The beam wander and beam radius can also be evaluated under the condition that the receiving aperture is large enough and the speckle would not leave the Fresnel lens because of the beam wander effect. The error of CCD pixel response non-uniformity and its influence and the calibration of CCD irradiance response function and image geometric projection coefficient are discussed. The experiments show that this system is feasible for the monitoring of far field speckle characteristic parameters in the laser atmospheric propagation. Especially for the free space optical communication, it can prove experiment data support on the slow fading research of median level and optimal design of detection threshold under the complex influence of atmospheric extinction and various kinds of turbulence effects.
In order to systematically evaluate the characteristic parameters of far field speckle in the real atmosphere condition and analyze the influence of laser atmospheric propagation on the optoelectronic system, a monitoring method is presented using large aperture projection optics. The projection optics is made of low cost and large aperture Fresnel lens, which can project the irradiance distribution of far field speckle on the CCD detector. The receiving power and scintillation index on a certain aperture can be evaluated through CCD imaging process. The beam wander and beam radius can also be evaluated under the condition that the receiving aperture is large enough and the speckle would not leave the Fresnel lens because of the beam wander effect. The error of CCD pixel response non-uniformity and its influence and the calibration of CCD irradiance response function and image geometric projection coefficient are discussed. The experiments show that this system is feasible for the monitoring of far field speckle characteristic parameters in the laser atmospheric propagation. Especially for the free space optical communication, it can prove experiment data support on the slow fading research of median level and optimal design of detection threshold under the complex influence of atmospheric extinction and various kinds of turbulence effects.
2014,
26: 081022.
doi: 10.11884/HPLPB201426.081022
Abstract:
We report a coherent combining of two 120 W solid state lasers with good beam quality. Laser beams from two slab laser amplifiers are reshaped into square beam. Up to 92.4% fill factor is achieved by splicing system with small gaps. A compact optical system with high sampling frequency is designed to detect the optical axis of slab lasers. A fast steering mirror (FSM) system driven by piezoelectric ceramics is applied to stabilizing the lasers. When the FSM systemworks, the root mean square error of the optical axis is significantly reduced to be less that 2 micro radians. The piston phase of two lasers is locked by a fast dithering system based on field programmable gate array (FPGA) using stochastic parallel gradient descent(SPGD) algorithm. After coherent beam combination, the peak intensity of the far-field spot is increased by a factor of 1.7, reaching 84% of the ideal case. When the beams are in phase, the BQ of the combined laser beam is 1.1, which means that more than 67% of the total energy is locked in the main lobe.
We report a coherent combining of two 120 W solid state lasers with good beam quality. Laser beams from two slab laser amplifiers are reshaped into square beam. Up to 92.4% fill factor is achieved by splicing system with small gaps. A compact optical system with high sampling frequency is designed to detect the optical axis of slab lasers. A fast steering mirror (FSM) system driven by piezoelectric ceramics is applied to stabilizing the lasers. When the FSM systemworks, the root mean square error of the optical axis is significantly reduced to be less that 2 micro radians. The piston phase of two lasers is locked by a fast dithering system based on field programmable gate array (FPGA) using stochastic parallel gradient descent(SPGD) algorithm. After coherent beam combination, the peak intensity of the far-field spot is increased by a factor of 1.7, reaching 84% of the ideal case. When the beams are in phase, the BQ of the combined laser beam is 1.1, which means that more than 67% of the total energy is locked in the main lobe.
2014,
26: 081023.
doi: 10.11884/HPLPB201426.081023
Abstract:
Based on Fresnel-Kirchhoff diffraction integral theory, output beam properties of fiber-coupled LD array and their impacts on oscillating light are examined. The results show that deviating from Gaussian distribution, the output light intensity on the exit surface of the optical fiber is in multi-peak distribution. Positions of peaks are sensitive to LD beam directions, and will change with the variation of LD beam directional angle and spatial location. This phenomenon is a result of various factors. Pump light with multi-peak distribution has a direct impact on the mode structure of the oscillating light. The more pump light intensity peaks concentrate in center, and the more convex of the light intensity is, the better oscillating light beam quality will be, which should be considered in laser-diode pumped solid-state lasers design.
Based on Fresnel-Kirchhoff diffraction integral theory, output beam properties of fiber-coupled LD array and their impacts on oscillating light are examined. The results show that deviating from Gaussian distribution, the output light intensity on the exit surface of the optical fiber is in multi-peak distribution. Positions of peaks are sensitive to LD beam directions, and will change with the variation of LD beam directional angle and spatial location. This phenomenon is a result of various factors. Pump light with multi-peak distribution has a direct impact on the mode structure of the oscillating light. The more pump light intensity peaks concentrate in center, and the more convex of the light intensity is, the better oscillating light beam quality will be, which should be considered in laser-diode pumped solid-state lasers design.
2014,
26: 082001.
doi: 10.11884/HPLPB201426.082001
Abstract:
Ag nanoclusters are prepared by plasma gas condensation method, The parameter dependences of Ag nanoclusters are also studied. The particle diameter and size distribution are measured by in-situ quadrupole mass filter and compared with the analysis of transmission electron microscope (TEM). The results show that keeping other parameters fixed, the average size increases gradually with the increase of sputtering current, aggregation zone length and Ar flow rate, respectively. However, it decreases when the Ar gas flow rate is more than 60 mL/min. The addition of He in Ar gas causes the decline of the average size, which can be enhanced by increasing the He flow rate. The sputtering current and Ar flow rate are key parameters affecting the average size of Ag nanoclusters.The TEM results show that average size of Ag nanoclusters is 2, 4 and 6 nm, respectively by adjusting the parameters. It is also indicated that the size and distribution data of Ag nanoclusters by TEM analysis and in situ quadrupole mass spectrometer are consistent.
Ag nanoclusters are prepared by plasma gas condensation method, The parameter dependences of Ag nanoclusters are also studied. The particle diameter and size distribution are measured by in-situ quadrupole mass filter and compared with the analysis of transmission electron microscope (TEM). The results show that keeping other parameters fixed, the average size increases gradually with the increase of sputtering current, aggregation zone length and Ar flow rate, respectively. However, it decreases when the Ar gas flow rate is more than 60 mL/min. The addition of He in Ar gas causes the decline of the average size, which can be enhanced by increasing the He flow rate. The sputtering current and Ar flow rate are key parameters affecting the average size of Ag nanoclusters.The TEM results show that average size of Ag nanoclusters is 2, 4 and 6 nm, respectively by adjusting the parameters. It is also indicated that the size and distribution data of Ag nanoclusters by TEM analysis and in situ quadrupole mass spectrometer are consistent.
2014,
26: 082002.
doi: 10.11884/HPLPB201426.082002
Abstract:
High non-LTE issue of ionization and radiative transfer are important physical characteristics of the laser-target hohlraum. Detailed multi-group transport approximation under non-LTE atomic physics is necessary for precisely describing radiation transfer and its interaction with matter. Using the recently developed LARED-integration code, we have accomplished multi-group radiative transfer calculations of the laser-target experimental hohlraum in 2D. Numerical results reflect the radiative illumination ununiformity inside the hohlraum. The ratio of X-ray intensity of the laser spot versus other regions along the gold wall agrees well with that of the experimental result, meanwhile the measured and simulated fuel shape resembles each other closely.
High non-LTE issue of ionization and radiative transfer are important physical characteristics of the laser-target hohlraum. Detailed multi-group transport approximation under non-LTE atomic physics is necessary for precisely describing radiation transfer and its interaction with matter. Using the recently developed LARED-integration code, we have accomplished multi-group radiative transfer calculations of the laser-target experimental hohlraum in 2D. Numerical results reflect the radiative illumination ununiformity inside the hohlraum. The ratio of X-ray intensity of the laser spot versus other regions along the gold wall agrees well with that of the experimental result, meanwhile the measured and simulated fuel shape resembles each other closely.
2014,
26: 082003.
doi: 10.11884/HPLPB201426.082003
Abstract:
Laser-induced X-ray source is widely used in high energy density physics. The experiment studied the Pd L-band X-ray source produced from the 9th laser (400 J/1 ns/351 nm) irradiating 10 m Pd targets on Shenguang Ⅱ facility. The emission spectrum of Pd L-band X-ray was 2.9-3.6 keV. The conversion efficient of Pd L-band X-ray was 8%. The angular distributions measured in front of the targets could be fitted with the function of cos1/3. The experimental result shows that the Pd X-ray source has the advantage of proper X-ray wavelength and high brightness.
Laser-induced X-ray source is widely used in high energy density physics. The experiment studied the Pd L-band X-ray source produced from the 9th laser (400 J/1 ns/351 nm) irradiating 10 m Pd targets on Shenguang Ⅱ facility. The emission spectrum of Pd L-band X-ray was 2.9-3.6 keV. The conversion efficient of Pd L-band X-ray was 8%. The angular distributions measured in front of the targets could be fitted with the function of cos1/3. The experimental result shows that the Pd X-ray source has the advantage of proper X-ray wavelength and high brightness.
2014,
26: 082004.
doi: 10.11884/HPLPB201426.082004
Abstract:
To improve the reliability of xenon lamps in optical amplifier of inertial confinement fusion (ICF) facility, high power xenon lamps were tested with the power modules similar to NIF facility in US. Though operating at a relatively safe energy loading factor of 0.2 or so, unexpected behavior of some lamps was observed while peak power value of discharge pulse was higher than 300 mega watts. Milky white participants appeared in the inner surface of the quartz envelope opposite to metallic reflector inside amplifier. Scanning electron microscopy and X-ray photoelectron spectroscopy data demonstrated that the chemical composition of whitish participant was SiO2. To understand the thermal damage mechanism of the lamp envelope, the plasma channel profiles were captured by a high speed CCD camera. The photographs indicated that the existence of metallic reflector beside silica envelope resulted in an uneven distribution of plasma. The temperature was higher in the region with high plasma density. This leaded to local evaporation of silica glass and the whitening of quartz envelope. The results are helpful to optimize the design of discharge circuit of power module and reflector of amplifier of ICF facility.
To improve the reliability of xenon lamps in optical amplifier of inertial confinement fusion (ICF) facility, high power xenon lamps were tested with the power modules similar to NIF facility in US. Though operating at a relatively safe energy loading factor of 0.2 or so, unexpected behavior of some lamps was observed while peak power value of discharge pulse was higher than 300 mega watts. Milky white participants appeared in the inner surface of the quartz envelope opposite to metallic reflector inside amplifier. Scanning electron microscopy and X-ray photoelectron spectroscopy data demonstrated that the chemical composition of whitish participant was SiO2. To understand the thermal damage mechanism of the lamp envelope, the plasma channel profiles were captured by a high speed CCD camera. The photographs indicated that the existence of metallic reflector beside silica envelope resulted in an uneven distribution of plasma. The temperature was higher in the region with high plasma density. This leaded to local evaporation of silica glass and the whitening of quartz envelope. The results are helpful to optimize the design of discharge circuit of power module and reflector of amplifier of ICF facility.
2014,
26: 082005.
doi: 10.11884/HPLPB201426.082005
Abstract:
The gas fill near the Au wall along the inner laser cone is the main region which stimulates SRS instabilities. At this region, pressure balance and energy balance between the inside and the outside of inner laser cone path are obtained. A plasma scaling model in ignition hohlraum of ICF has been developed. Capsule performance, laser facility parameters, and laser-plasma interaction (LPI) physics are related by this scaling model. A 350 eV ignition hohlraum design is proposed according to the model. Compared with the designs published before, this design could reduce LPI development of inner laser cones better, but put forward more pressure on laser facility design.
The gas fill near the Au wall along the inner laser cone is the main region which stimulates SRS instabilities. At this region, pressure balance and energy balance between the inside and the outside of inner laser cone path are obtained. A plasma scaling model in ignition hohlraum of ICF has been developed. Capsule performance, laser facility parameters, and laser-plasma interaction (LPI) physics are related by this scaling model. A 350 eV ignition hohlraum design is proposed according to the model. Compared with the designs published before, this design could reduce LPI development of inner laser cones better, but put forward more pressure on laser facility design.
2014,
26: 082006.
doi: 10.11884/HPLPB201426.082006
Abstract:
To measure the sweep nonlinearity of streak camera working at microsecond level, the system based on delay tunable signal source is developed and analyzed. The system is mainly constituted of a delay tunable signal source and a triggered short pulse laser. The short pulse laser is triggered by the delay tunable signal source. The streak camera records the laser pulses appearing at different channel of the streak camera as the signal sources delay value varies. The relation between the laser pulse peak channel and signal source delay value is fitted by the polynomial method. The polynomial is a denotation of the correlation between time and each channel. Sweep velocity and sweep nonlinearity are calculated with the polynomial. The fluctuation of the sweep nonlinearity measurement system is 0.7 ns. The fluctuation of the system causes the fluctuation of the measured sweep velocity through curve fitting process. The process is simulated by adding a Gaussian noise to the delay-channel raw data points. The mass simulation shows that the fluctuation of the delay-channel correlation is less than 2 ns. The sweep nonlinearity measurement system can also be used for calibrating streak camera working at several hundred nanosecond level.
To measure the sweep nonlinearity of streak camera working at microsecond level, the system based on delay tunable signal source is developed and analyzed. The system is mainly constituted of a delay tunable signal source and a triggered short pulse laser. The short pulse laser is triggered by the delay tunable signal source. The streak camera records the laser pulses appearing at different channel of the streak camera as the signal sources delay value varies. The relation between the laser pulse peak channel and signal source delay value is fitted by the polynomial method. The polynomial is a denotation of the correlation between time and each channel. Sweep velocity and sweep nonlinearity are calculated with the polynomial. The fluctuation of the sweep nonlinearity measurement system is 0.7 ns. The fluctuation of the system causes the fluctuation of the measured sweep velocity through curve fitting process. The process is simulated by adding a Gaussian noise to the delay-channel raw data points. The mass simulation shows that the fluctuation of the delay-channel correlation is less than 2 ns. The sweep nonlinearity measurement system can also be used for calibrating streak camera working at several hundred nanosecond level.
2014,
26: 083001.
doi: 10.11884/HPLPB201426.083001
Abstract:
Responses of n-Si detecting sample to TE10 mode submillimeter wave in an overmoded rectangular waveguide are numerically investigated. Relative sensitivity under fundamental mode operation for the submillimeter wave detecting structure is derived. Using a three-dimensional electromagnetic finite-difference time-domain method, the interaction of the n-Si sample with submillimeter wave within 300-400 GHz in the overmoded waveguide is calculated, and the dependences of voltage standing wave ratio (VSWR) of the structure and average electric field strength in the sample on the parameters of n-Si detecting sample are analyzed. Compared with the fundamental mode detecting structure with the same silicon sample, VSWR and average electric field strength in the sample change slightly in the overmoded detecting structure, while the fluctuations of their dependences on frequency increase. Selection of the structural parameters of the overmoded detecting structure is also studied. In working frequency range of 300-400 GHz, the optimized structure with VSWR less than 2.75 (no more than 1.8 within frequency range of 335-380 GHz) and response time of hundreds of picoseconds-level has a relative sensitivity around 0.127 kW-1 fluctuating within 20.5% and the maximum enduring power of about 0.53 kW. This detecting structure satisfies the demand of the direct detection of large power pulses at submillimeter wavelength.
Responses of n-Si detecting sample to TE10 mode submillimeter wave in an overmoded rectangular waveguide are numerically investigated. Relative sensitivity under fundamental mode operation for the submillimeter wave detecting structure is derived. Using a three-dimensional electromagnetic finite-difference time-domain method, the interaction of the n-Si sample with submillimeter wave within 300-400 GHz in the overmoded waveguide is calculated, and the dependences of voltage standing wave ratio (VSWR) of the structure and average electric field strength in the sample on the parameters of n-Si detecting sample are analyzed. Compared with the fundamental mode detecting structure with the same silicon sample, VSWR and average electric field strength in the sample change slightly in the overmoded detecting structure, while the fluctuations of their dependences on frequency increase. Selection of the structural parameters of the overmoded detecting structure is also studied. In working frequency range of 300-400 GHz, the optimized structure with VSWR less than 2.75 (no more than 1.8 within frequency range of 335-380 GHz) and response time of hundreds of picoseconds-level has a relative sensitivity around 0.127 kW-1 fluctuating within 20.5% and the maximum enduring power of about 0.53 kW. This detecting structure satisfies the demand of the direct detection of large power pulses at submillimeter wavelength.
2014,
26: 083003.
doi: 10.11884/HPLPB201426.083003
Abstract:
A circular waveguide TM01-TE11 mode converter filled with metal shell and metal plate is proposed . The circular waveguide is split into two semi-circle sectors: one semi-circle sector is a regular empty waveguide, the other is an empty semi-circle waveguide filled with a metal shell and metal plate to adjust its radius. The numerical simulation results show that the reflection is below 0.01 and the conversion efficiency reaches 99.56% at the center frequency 2.8 GHz, and the S11 is below -10 dB and the conversion efficiency exceeds 90% at the frequency range from 2.716 GHz to 2.946 GHz. The results of S11 obtained by experiment are in agreement with that of the simulation, which validates the design and simulation of the mode converter.
A circular waveguide TM01-TE11 mode converter filled with metal shell and metal plate is proposed . The circular waveguide is split into two semi-circle sectors: one semi-circle sector is a regular empty waveguide, the other is an empty semi-circle waveguide filled with a metal shell and metal plate to adjust its radius. The numerical simulation results show that the reflection is below 0.01 and the conversion efficiency reaches 99.56% at the center frequency 2.8 GHz, and the S11 is below -10 dB and the conversion efficiency exceeds 90% at the frequency range from 2.716 GHz to 2.946 GHz. The results of S11 obtained by experiment are in agreement with that of the simulation, which validates the design and simulation of the mode converter.
2014,
26: 083004.
doi: 10.11884/HPLPB201426.083004
Abstract:
A metallic photonic crystal loaded transmission line is studied, and a metallic photonic crystal type TEM-TE11 mode converter which is suitable for narrow band high power microwave application is designed according to its electromagnetic properties. Metallic photonic crystal is partially filled along azimuthal direction in the device to achieve phase-shifting. A three-row structure is designed and simulated by commercial software CST Microwave Studio. The simulation results show that its conversion efficiency is 99% at the center frequency 1.57 GHz. In the frequency range of 1.533-1.609 GHz, the conversion efficiency exceeds 90%, with a corresponding bandwidth of 4.8%. A TEM mode excitation and a horn antenna is fabricated and the performance of mode converter is tested. The results confirm the design.
A metallic photonic crystal loaded transmission line is studied, and a metallic photonic crystal type TEM-TE11 mode converter which is suitable for narrow band high power microwave application is designed according to its electromagnetic properties. Metallic photonic crystal is partially filled along azimuthal direction in the device to achieve phase-shifting. A three-row structure is designed and simulated by commercial software CST Microwave Studio. The simulation results show that its conversion efficiency is 99% at the center frequency 1.57 GHz. In the frequency range of 1.533-1.609 GHz, the conversion efficiency exceeds 90%, with a corresponding bandwidth of 4.8%. A TEM mode excitation and a horn antenna is fabricated and the performance of mode converter is tested. The results confirm the design.
2014,
26: 083005.
doi: 10.11884/HPLPB201426.083005
Abstract:
A double-beam magnetron injection gun was used to improve the output power of gyrotrons. A double-beam magnetron injection gun can output two relativistic electron beams, which is a better way to raise the current of the magnetron injection gun without reducing the quality of electron beams. Compared with the double-anode magnetron injection gun with the same output current, the double-beam magnetron injection gun can reduce velocity spread and improve the quality of electron beams, because of its smaller influence of the space charge. Using the software MAGIC, a double-beam magnetron injection gun with a modest velocity ratio and a low velocity spread of electron beams was designed.
A double-beam magnetron injection gun was used to improve the output power of gyrotrons. A double-beam magnetron injection gun can output two relativistic electron beams, which is a better way to raise the current of the magnetron injection gun without reducing the quality of electron beams. Compared with the double-anode magnetron injection gun with the same output current, the double-beam magnetron injection gun can reduce velocity spread and improve the quality of electron beams, because of its smaller influence of the space charge. Using the software MAGIC, a double-beam magnetron injection gun with a modest velocity ratio and a low velocity spread of electron beams was designed.
2014,
26: 083006.
doi: 10.11884/HPLPB201426.083006
Abstract:
A statistical method is used to analyze the evolutions of the important physical values in the dielectric single-surface multipactor discharge process with the number of collisions, such as the number of second emission electron, DC field, deposited power on dielectric, and electron transit time, considering the emission energy and launch angles of the emitted electrons, the phase distribution of the RF field. How angles and reflection coefficients affect the multipactor is also studied. The results show that when a certain tilt dc field is imposed, the smaller the reflection coefficient is, and the longer the delay time of the avalanche breakdown and the greater the number of secondary emission electrons in the steady state are. When the dc field is parallel to the surface of the dielectric plate and the RF field is specified, the higher the electric field amplitude is, the longer the delay time of the avalanche breakdown is and the greater the number of secondary emission electrons in the saturation are, but if the amplitude exceeds a certain value, the multipactor will not occur. When the DC is vertical to the surface of the dielectric plate, the higher the electric field amplitude is, the longer the delay time of the avalanche breakdown is and the smaller the number of the secondary electron in saturation are. Similarly, if the amplitude exceeds a certain value, the multipactor will also not occur.
A statistical method is used to analyze the evolutions of the important physical values in the dielectric single-surface multipactor discharge process with the number of collisions, such as the number of second emission electron, DC field, deposited power on dielectric, and electron transit time, considering the emission energy and launch angles of the emitted electrons, the phase distribution of the RF field. How angles and reflection coefficients affect the multipactor is also studied. The results show that when a certain tilt dc field is imposed, the smaller the reflection coefficient is, and the longer the delay time of the avalanche breakdown and the greater the number of secondary emission electrons in the steady state are. When the dc field is parallel to the surface of the dielectric plate and the RF field is specified, the higher the electric field amplitude is, the longer the delay time of the avalanche breakdown is and the greater the number of secondary emission electrons in the saturation are, but if the amplitude exceeds a certain value, the multipactor will not occur. When the DC is vertical to the surface of the dielectric plate, the higher the electric field amplitude is, the longer the delay time of the avalanche breakdown is and the smaller the number of the secondary electron in saturation are. Similarly, if the amplitude exceeds a certain value, the multipactor will also not occur.
2014,
26: 083007.
doi: 10.11884/HPLPB201426.083007
Abstract:
A coaxial corrugated reflector and smooth drift segments structure of relativistic diffraction generator were studied using the full three-dimensional particle simulation software CHIPIC. The influences of the drift segments and reflector on the output power were analyzed. The relationship between the reflector position and the output power was explored. The simulation results show that appropriate reflector and drift segments can greatly improve the output power. After optimization of the structure parameters, when the input voltage was 480 kV, the average output power achieved 774.5 MW and the average power efficiency attained 32.3%.
A coaxial corrugated reflector and smooth drift segments structure of relativistic diffraction generator were studied using the full three-dimensional particle simulation software CHIPIC. The influences of the drift segments and reflector on the output power were analyzed. The relationship between the reflector position and the output power was explored. The simulation results show that appropriate reflector and drift segments can greatly improve the output power. After optimization of the structure parameters, when the input voltage was 480 kV, the average output power achieved 774.5 MW and the average power efficiency attained 32.3%.
2014,
26: 083008.
doi: 10.11884/HPLPB201426.083008
Abstract:
Neural network method is applied to processing exploration data of high power microwave(HPM). A HPM exploration prognosticating model based on analyzing HPM characteristic parameters and creating a HPM characteristic parameters data-base is established. Results can be reverted with training samples by this model. The model shows good ability on predicting. This data processing method can be used in classing or prognosticating exploration data, especially in complex data processing.
Neural network method is applied to processing exploration data of high power microwave(HPM). A HPM exploration prognosticating model based on analyzing HPM characteristic parameters and creating a HPM characteristic parameters data-base is established. Results can be reverted with training samples by this model. The model shows good ability on predicting. This data processing method can be used in classing or prognosticating exploration data, especially in complex data processing.
2014,
26: 083009.
doi: 10.11884/HPLPB201426.083009
Abstract:
Sealing a TEM horn antenna in a nylon radome filled with transformer oil can enhance the power capacity, and improve the performance of the TEM horn antenna as long as a beam focusing lens is formed by the nylon shell filled with transformer oil. On the basis of the ellipses geometrical properties and the shrinkage of wavelength in a medium, an ellipsoidal transformer oil lens was designed with the help of geometrical optics theory. The theory says that the shrinkage of the wavelength in transformer oil enlarges the electrical size of the TEM horn will preliminarily improve the performance of the TEM horn antenna, and the beam focusing characteristics of the ellipsoidal transformer oil lens will further improve the performance of the TEM horn antenna. In order to prove the correctness of the theoretical analysis, a spherical transformer oil lens without beam focusing characteristics was designed as comparison, and the simulation results agreed well with the theoretical analysis. Compared with the TEM horn in atmosphere, the ellipsoidal transformer oil lens narrowed down the main beam and increased the rEpp by 56.97%, and the low boundary point of the impedance bandwidth reached 0.2 GHz from 0.28 GHz. The power capacity of the ellipsoidal transformer oil lens TEM horn antenna reached 18.43 GW.
Sealing a TEM horn antenna in a nylon radome filled with transformer oil can enhance the power capacity, and improve the performance of the TEM horn antenna as long as a beam focusing lens is formed by the nylon shell filled with transformer oil. On the basis of the ellipses geometrical properties and the shrinkage of wavelength in a medium, an ellipsoidal transformer oil lens was designed with the help of geometrical optics theory. The theory says that the shrinkage of the wavelength in transformer oil enlarges the electrical size of the TEM horn will preliminarily improve the performance of the TEM horn antenna, and the beam focusing characteristics of the ellipsoidal transformer oil lens will further improve the performance of the TEM horn antenna. In order to prove the correctness of the theoretical analysis, a spherical transformer oil lens without beam focusing characteristics was designed as comparison, and the simulation results agreed well with the theoretical analysis. Compared with the TEM horn in atmosphere, the ellipsoidal transformer oil lens narrowed down the main beam and increased the rEpp by 56.97%, and the low boundary point of the impedance bandwidth reached 0.2 GHz from 0.28 GHz. The power capacity of the ellipsoidal transformer oil lens TEM horn antenna reached 18.43 GW.
2014,
26: 083010.
doi: 10.11884/HPLPB201426.083010
Abstract:
Resorting to PIC simulation and experimental investigation, the relation between the output microwave width (power efficiency) and the input triangle voltage waveform for a magnetically insulated transmission line oscillator (MILO) is analyzed without power capability problem. The analysis results show that: (a) On the condition of the same width of the input voltage, with the increasing of the amplitude of the input voltage, the putout microwave bottom width and the FWHW increase; and the power efficiency increase firstly and then decrease when the power is saturated. (b) On the condition of the same amplitude of the input voltage, with the increasing of the rising edge (with stable slope) of the input voltage, the putout microwave width increases; and the power efficiency decreases. Therefore, on the condition of the limited pulse width of the input voltage, by the way of increasing the rising edge of the input voltage, the output microwave width can be increased. And on the condition of the limited amplitude of the input voltage, by the way of decreasing the rise-time of the input voltage, the output microwave power can be increased. With the proper input voltage parameter, the matching problem of the key parameters between the microwave power and the width for a MILO on the condition of the input triangle voltage is solved.
Resorting to PIC simulation and experimental investigation, the relation between the output microwave width (power efficiency) and the input triangle voltage waveform for a magnetically insulated transmission line oscillator (MILO) is analyzed without power capability problem. The analysis results show that: (a) On the condition of the same width of the input voltage, with the increasing of the amplitude of the input voltage, the putout microwave bottom width and the FWHW increase; and the power efficiency increase firstly and then decrease when the power is saturated. (b) On the condition of the same amplitude of the input voltage, with the increasing of the rising edge (with stable slope) of the input voltage, the putout microwave width increases; and the power efficiency decreases. Therefore, on the condition of the limited pulse width of the input voltage, by the way of increasing the rising edge of the input voltage, the output microwave width can be increased. And on the condition of the limited amplitude of the input voltage, by the way of decreasing the rise-time of the input voltage, the output microwave power can be increased. With the proper input voltage parameter, the matching problem of the key parameters between the microwave power and the width for a MILO on the condition of the input triangle voltage is solved.
2014,
26: 083101.
doi: 10.11884/HPLPB201426.083101
Abstract:
The characteristics of Q factor in dual-grating diffraction radiation device were studied, and the influence of structural parameters of resonant cavity on Q factor was discussed. The results show that the Q factor in cavity resonator is significantly affected by the width of the rectangular cavity and the length of the spherical open cavity. Compared with Orotron, the impact on Q factor of grating is much smaller in dual-grating diffraction radiation device, and the increments of both grating width and grating depth would lead to decreasing of Q factor.
The characteristics of Q factor in dual-grating diffraction radiation device were studied, and the influence of structural parameters of resonant cavity on Q factor was discussed. The results show that the Q factor in cavity resonator is significantly affected by the width of the rectangular cavity and the length of the spherical open cavity. Compared with Orotron, the impact on Q factor of grating is much smaller in dual-grating diffraction radiation device, and the increments of both grating width and grating depth would lead to decreasing of Q factor.
2014,
26: 083102.
doi: 10.11884/HPLPB201426.083102
Abstract:
A THz free electron laser (FEL-THz) is being constructed in China Academy of Engineering Physics (CAEP) with the aim of proving high-power, monochromatic and tunable radiation for research in a variety of experimental fields. This facility consists of an injector equipped with a photo-cathode direct current gun, an achromatic transfer line, and an undulator for THz radiation. The physical design of the beamline is accomplished with the PARMELA and TRANSPORT programs. Start-to-end simulation is performed and the result is crosschecked with the codes of IMPACT-T and ELEGANT. The results show that it is feasible to achieve an electron beam with energy of 7~8 MeV, beam current of about 5 mA, and normalized transverse emittance typically below 10 mmmrad at the entrance of the undulator.
A THz free electron laser (FEL-THz) is being constructed in China Academy of Engineering Physics (CAEP) with the aim of proving high-power, monochromatic and tunable radiation for research in a variety of experimental fields. This facility consists of an injector equipped with a photo-cathode direct current gun, an achromatic transfer line, and an undulator for THz radiation. The physical design of the beamline is accomplished with the PARMELA and TRANSPORT programs. Start-to-end simulation is performed and the result is crosschecked with the codes of IMPACT-T and ELEGANT. The results show that it is feasible to achieve an electron beam with energy of 7~8 MeV, beam current of about 5 mA, and normalized transverse emittance typically below 10 mmmrad at the entrance of the undulator.
2014,
26: 083103.
doi: 10.11884/HPLPB201426.083103
Abstract:
A thorough performance analysis of a type of sensing element, which is designed and manufactured for application to high power terahertz pulse measurement based on hot electrons effect in semiconductor, is carried out by measuring the geometric and electric parameters. Sensing elements achieve a little deviation from the optimal value and an excellent ohmic touch. The deviation of the sensing element has little effect on the relative sensitivity, as the simulation result shows. Validity of the manufacturing techniques for the sensing element is proved by making a synthesis of all the parameters during the whole course of the measurement.
A thorough performance analysis of a type of sensing element, which is designed and manufactured for application to high power terahertz pulse measurement based on hot electrons effect in semiconductor, is carried out by measuring the geometric and electric parameters. Sensing elements achieve a little deviation from the optimal value and an excellent ohmic touch. The deviation of the sensing element has little effect on the relative sensitivity, as the simulation result shows. Validity of the manufacturing techniques for the sensing element is proved by making a synthesis of all the parameters during the whole course of the measurement.
2014,
26: 083104.
doi: 10.11884/HPLPB201426.083104
Abstract:
Perturbed dispersion relation considering the ohmic losses of the waveguide wall in folded waveguide tube is derived and solved by using Matlab. Small signal gain increases with the increasing of ratio of the center frequency to the cutoff frequency, but the increase will be slower with further increasing of the ratio and the band width becomes narrower, as calculation results show. With the beam current density fixed, there exist optimal values of the width of the beam tunnel and the width of the cross section for the maximum gain. A quiescent waveguide mode propagating backward appears in the waveguide while taking the ohmic losses into consideration. With the increasing of the operating frequency, the gain decreases obviously while the intensity of the quiescent waveguide mode is enhanced. Therefore, for a folded waveguide tube operating at higher frequency in terahertz band, the period number of the folded waveguide increases correspondingly.
Perturbed dispersion relation considering the ohmic losses of the waveguide wall in folded waveguide tube is derived and solved by using Matlab. Small signal gain increases with the increasing of ratio of the center frequency to the cutoff frequency, but the increase will be slower with further increasing of the ratio and the band width becomes narrower, as calculation results show. With the beam current density fixed, there exist optimal values of the width of the beam tunnel and the width of the cross section for the maximum gain. A quiescent waveguide mode propagating backward appears in the waveguide while taking the ohmic losses into consideration. With the increasing of the operating frequency, the gain decreases obviously while the intensity of the quiescent waveguide mode is enhanced. Therefore, for a folded waveguide tube operating at higher frequency in terahertz band, the period number of the folded waveguide increases correspondingly.
2014,
26: 083105.
doi: 10.11884/HPLPB201426.083105
Abstract:
In order to increase the output power of THz traveling-wave tube(TWT), by parallel multi-beam and power combining method, theoretical analysis and numerical simulation of parallel multi-beam D band folded TWT waveguide have been done, and simulation results demonstrate that the method can achieve the power combining output of multi-amplified signals. The results show: the single-beam mode TWT owns flat dispersion characteristics between 0.135 THz and 0.157 THz. The 3 dB gain band is 13 GHz and the largest gain is 20.88 dB at 0.14 THz. The multi-beam mode TWT got 20.8 dB combining gain at 0.14 THz and the combining efficiency is not below 92% in 3 dB gain frequency range. The parallel multi-beam mode TWT has many merits, such as high output power, small single-beam current and lower focusing magnetic field. The study helps achieving high power THz radiation basing on the present heat cathode level.
In order to increase the output power of THz traveling-wave tube(TWT), by parallel multi-beam and power combining method, theoretical analysis and numerical simulation of parallel multi-beam D band folded TWT waveguide have been done, and simulation results demonstrate that the method can achieve the power combining output of multi-amplified signals. The results show: the single-beam mode TWT owns flat dispersion characteristics between 0.135 THz and 0.157 THz. The 3 dB gain band is 13 GHz and the largest gain is 20.88 dB at 0.14 THz. The multi-beam mode TWT got 20.8 dB combining gain at 0.14 THz and the combining efficiency is not below 92% in 3 dB gain frequency range. The parallel multi-beam mode TWT has many merits, such as high output power, small single-beam current and lower focusing magnetic field. The study helps achieving high power THz radiation basing on the present heat cathode level.
2014,
26: 083201.
doi: 10.11884/HPLPB201426.083201
Abstract:
In order to study effect on electromagnetic field in enclosure affected by penetrating conducting and its circuit, different models of penetrating and its circuit were established. Electromagnetic simulation software CST was used to do simulation. Experimental system was set up with a GTEM chamber, a vector network analyzer, a power amplifier and an ETS electric field probe to verify simulation results. Laws of influence on electromagnetic field in enclosure by penetrating conductor coupling and its terminal load effect were revealed. The results show that electromagnetic field in enclosure is affected by the combination of penetrating conductor resonance and enclosure resonance. Electric field strength got extremum at resonant frequency. Shielding effectiveness curve of penetrating conductor open at two terminals was close to the curve of penetrating conductor loading but not grounding model. Electric field of penetrating conductor loading grounding directly was significantly lower while resonant frequency was reduced. Changing laws of penetrating conductor loading floating grounding was similar to model of penetrating conductor loading but not grounding in low frequency and similar to model of penetrating conductor loading grounding directly in high frequency. The value of resistance and capacity at terminal of penetrating conductor can also affect electric field.
In order to study effect on electromagnetic field in enclosure affected by penetrating conducting and its circuit, different models of penetrating and its circuit were established. Electromagnetic simulation software CST was used to do simulation. Experimental system was set up with a GTEM chamber, a vector network analyzer, a power amplifier and an ETS electric field probe to verify simulation results. Laws of influence on electromagnetic field in enclosure by penetrating conductor coupling and its terminal load effect were revealed. The results show that electromagnetic field in enclosure is affected by the combination of penetrating conductor resonance and enclosure resonance. Electric field strength got extremum at resonant frequency. Shielding effectiveness curve of penetrating conductor open at two terminals was close to the curve of penetrating conductor loading but not grounding model. Electric field of penetrating conductor loading grounding directly was significantly lower while resonant frequency was reduced. Changing laws of penetrating conductor loading floating grounding was similar to model of penetrating conductor loading but not grounding in low frequency and similar to model of penetrating conductor loading grounding directly in high frequency. The value of resistance and capacity at terminal of penetrating conductor can also affect electric field.
2014,
26: 084001.
doi: 10.11884/HPLPB201426.084001
Abstract:
60Co irradiation on optocouplers is examined at dose rate of 0.01, 0.1, 1.0 and 50 rad/s. The experimental results show that current transfer ratio decreases after exposure and the amplitude of degradation at a given total dose depends on the dose rate, namely more degradation with lower dose rate. The I-V characteristics of LED, gain and primary photocurrent of phototransistor, and transmission loss in optical coupling medium are tested and analyzed, which lead to a conclusion that photoresponse degradation in C-B region of phototransistor is the main contribution to CTR degradation of optocouplers.
60Co irradiation on optocouplers is examined at dose rate of 0.01, 0.1, 1.0 and 50 rad/s. The experimental results show that current transfer ratio decreases after exposure and the amplitude of degradation at a given total dose depends on the dose rate, namely more degradation with lower dose rate. The I-V characteristics of LED, gain and primary photocurrent of phototransistor, and transmission loss in optical coupling medium are tested and analyzed, which lead to a conclusion that photoresponse degradation in C-B region of phototransistor is the main contribution to CTR degradation of optocouplers.
2014,
26: 084002.
doi: 10.11884/HPLPB201426.084002
Abstract:
In order to provide optimization suggestions for the thermal design study on the 20 cm diameter LIPS-200 ion thruster with ring-cusp magnetic field, steady-state and transient thermal analysis are performed utilizing the calculation results with the internal discharge energy deposition mathematical model of the LIPS-200 ion thruster. Thermal balance experiments are conducted to validate these results. The results indicate that the internal magnet is the key factor influencing the thermal design of the thruster as the thruster is in steady operation, while increasing the surface emissivity of the internal and external components of the thruster can reduce the temperature of the internal components effectively, roughly by the order of 50~60 ℃. The thermal balance experiment results is in agreement with the theoretical analysis results.
In order to provide optimization suggestions for the thermal design study on the 20 cm diameter LIPS-200 ion thruster with ring-cusp magnetic field, steady-state and transient thermal analysis are performed utilizing the calculation results with the internal discharge energy deposition mathematical model of the LIPS-200 ion thruster. Thermal balance experiments are conducted to validate these results. The results indicate that the internal magnet is the key factor influencing the thermal design of the thruster as the thruster is in steady operation, while increasing the surface emissivity of the internal and external components of the thruster can reduce the temperature of the internal components effectively, roughly by the order of 50~60 ℃. The thermal balance experiment results is in agreement with the theoretical analysis results.
2014,
26: 084003.
doi: 10.11884/HPLPB201426.084003
Abstract:
The crossover phenomenon of transconductance curves was found in part of 0.5 m multi-finger NMOS FETs after irradiation experiments. To give a reasonable explanation, we assumed that the radiation effects on each gate of this part of multi-finger NMOS FETs are non-uniform, and the corresponding computer simulations were performed. The simulation results indicate that after non-uniform irradiation, the difference of oxide trapped charges and interface charges of each gate in multi-finger NMOS FETs will make threshold voltage shift asynchronously, leading to the degeneration of transconductance and the crossover of transconductance curves.
The crossover phenomenon of transconductance curves was found in part of 0.5 m multi-finger NMOS FETs after irradiation experiments. To give a reasonable explanation, we assumed that the radiation effects on each gate of this part of multi-finger NMOS FETs are non-uniform, and the corresponding computer simulations were performed. The simulation results indicate that after non-uniform irradiation, the difference of oxide trapped charges and interface charges of each gate in multi-finger NMOS FETs will make threshold voltage shift asynchronously, leading to the degeneration of transconductance and the crossover of transconductance curves.
2014,
26: 085001.
doi: 10.11884/HPLPB201426.085001
Abstract:
A trigger is designed based on VE4141 thyratron for the 100 kV Mini-Marx generator. The trigger meets the following design specifications: pulse voltage is up to 30 kV, falling time is less than 15 ns, pulse width is more than 500 ns. It can receive optical signal, electric signal and manual signal to trigger. Charge voltage can be adjusted and displayed by the control plane. Pre-trigger and trigger signals are received through an IGBT drive circuit, and are used to control the VE4141 thyratron to discharge and get a high voltage pulsed signal to trigger the 100 kV Mini-Marx generator.
A trigger is designed based on VE4141 thyratron for the 100 kV Mini-Marx generator. The trigger meets the following design specifications: pulse voltage is up to 30 kV, falling time is less than 15 ns, pulse width is more than 500 ns. It can receive optical signal, electric signal and manual signal to trigger. Charge voltage can be adjusted and displayed by the control plane. Pre-trigger and trigger signals are received through an IGBT drive circuit, and are used to control the VE4141 thyratron to discharge and get a high voltage pulsed signal to trigger the 100 kV Mini-Marx generator.
2014,
26: 085002.
doi: 10.11884/HPLPB201426.085002
Abstract:
Differential-output current loops (B-dot probes) were designed and calibrated to derive magnetically-insulated transmission line(MITL) current in the PTS facility. Nichrome films were used to shield the loops from sheath electrons. All the B-dots were calibrated insitu. A feeding structure was designed to drive the MITLs from load area. In order to realize uniform current distribution azimuthally, MITL was terminated with short-circuit rods at the end of the corresponding tri-plate water line. Then the B-dots at each level could be calibrated respectively. Frequency response analysis indicates that the using of nichrome film makes the high frequency characteristics worse for B-dots. It shows in experiments that B-dots upper limiting frequency is 50.3 MHz, which is satisfactory for current measurement in our experiments. It also shows that MITL current and load current are self-consistent. Current of each level and combined current of all levels are reasonable according to theoretical predictions.
Differential-output current loops (B-dot probes) were designed and calibrated to derive magnetically-insulated transmission line(MITL) current in the PTS facility. Nichrome films were used to shield the loops from sheath electrons. All the B-dots were calibrated insitu. A feeding structure was designed to drive the MITLs from load area. In order to realize uniform current distribution azimuthally, MITL was terminated with short-circuit rods at the end of the corresponding tri-plate water line. Then the B-dots at each level could be calibrated respectively. Frequency response analysis indicates that the using of nichrome film makes the high frequency characteristics worse for B-dots. It shows in experiments that B-dots upper limiting frequency is 50.3 MHz, which is satisfactory for current measurement in our experiments. It also shows that MITL current and load current are self-consistent. Current of each level and combined current of all levels are reasonable according to theoretical predictions.
2014,
26: 085003.
doi: 10.11884/HPLPB201426.085003
Abstract:
A vertical GaAs PCSS is fabricated with a thickness of 0.6 mm and a gap of 3 mm, and the triggering experiment is carried out by semiconductor laser diode. Along with enhanced electric field, the output voltage increases linearly, the output waveform is similar to the laser waveform. When bias electric field exceeds the threshold, the output voltage increases rapidly, and the output voltage impulse is faster than the laser impulse which shows PCSS turns into nonlinear mode. Except for the bias voltage, PCSS turning into nonlinear mode is also associated with the speed and the energy of the trigger light pulse. Experiment indicates that the higher trigger energy is, the faster the rise-time is, the more likely the working mode of PCSS turns into nonlinear and the needing electric field is lower. But when bias electric field falls under the threshold (about 6 kV in this experiment), PCSS can not turn into nonlinear, even if the trigger light energy is enhanced.
A vertical GaAs PCSS is fabricated with a thickness of 0.6 mm and a gap of 3 mm, and the triggering experiment is carried out by semiconductor laser diode. Along with enhanced electric field, the output voltage increases linearly, the output waveform is similar to the laser waveform. When bias electric field exceeds the threshold, the output voltage increases rapidly, and the output voltage impulse is faster than the laser impulse which shows PCSS turns into nonlinear mode. Except for the bias voltage, PCSS turning into nonlinear mode is also associated with the speed and the energy of the trigger light pulse. Experiment indicates that the higher trigger energy is, the faster the rise-time is, the more likely the working mode of PCSS turns into nonlinear and the needing electric field is lower. But when bias electric field falls under the threshold (about 6 kV in this experiment), PCSS can not turn into nonlinear, even if the trigger light energy is enhanced.
2014,
26: 085004.
doi: 10.11884/HPLPB201426.085004
Abstract:
In the electrode erosion process, melted and evaporated metal removed from electrode surface may contaminate the gas switch insulator and increase the probability of flashover accident, influencing the lifetime of gas switch and the stability of pulsed power system. In this paper, researches on the degradation of morphology and insulating strength of insulator surface were carried out while PMMA and brass were employed as the insulator and electrode material respectively. The results show that the electrode erosion would generate plenty of metal vapors and ejected droplets. The metal vapors would congeal and produce tiny metal powder covering the insulator, meanwhile, the ejected droplets would bombard the insulator and generate dense cracks and embed metal particles. After 300 shots, the leak current of insulator surface increased and the flashover electric field decreased, on the other hand, the surface insulation resistance in different regions had a great distinction, resulting in an uneven distribution of electric field. As a result, the flashover voltage decreased and the probability of flashover accident increased.
In the electrode erosion process, melted and evaporated metal removed from electrode surface may contaminate the gas switch insulator and increase the probability of flashover accident, influencing the lifetime of gas switch and the stability of pulsed power system. In this paper, researches on the degradation of morphology and insulating strength of insulator surface were carried out while PMMA and brass were employed as the insulator and electrode material respectively. The results show that the electrode erosion would generate plenty of metal vapors and ejected droplets. The metal vapors would congeal and produce tiny metal powder covering the insulator, meanwhile, the ejected droplets would bombard the insulator and generate dense cracks and embed metal particles. After 300 shots, the leak current of insulator surface increased and the flashover electric field decreased, on the other hand, the surface insulation resistance in different regions had a great distinction, resulting in an uneven distribution of electric field. As a result, the flashover voltage decreased and the probability of flashover accident increased.
2014,
26: 085005.
doi: 10.11884/HPLPB201426.085005
Abstract:
To extend the lifetime of gas switches used by linear transformer drivers (LTD), electrode erosion tests for different materials (molybdenum, brass, copper-tungsten alloy, high density graphite, stainless steel 304 and 321) were conducted. These electrodes were designed according to the geometry and switching ability of the 200 kV low jitter multi-gap switches made before. Measurements show that under the condition of 20 kA peak current and 15.4 mC transferring charge, volume erosion rates decrease following the order of high density graphite, brass, copper-tungsten alloy, molybdenum and stainless steel. This relation, together with the electrode surface morphology images, shows that stainless steel works better than the other materials as LTD switch electrodes. According to the obtained volume erosion rates, the theoretical lifetime of an LTD switch using stainless steel electrodes could exceed 1 million times, provided that the insulation strength of the switch shell doesnt fail.
To extend the lifetime of gas switches used by linear transformer drivers (LTD), electrode erosion tests for different materials (molybdenum, brass, copper-tungsten alloy, high density graphite, stainless steel 304 and 321) were conducted. These electrodes were designed according to the geometry and switching ability of the 200 kV low jitter multi-gap switches made before. Measurements show that under the condition of 20 kA peak current and 15.4 mC transferring charge, volume erosion rates decrease following the order of high density graphite, brass, copper-tungsten alloy, molybdenum and stainless steel. This relation, together with the electrode surface morphology images, shows that stainless steel works better than the other materials as LTD switch electrodes. According to the obtained volume erosion rates, the theoretical lifetime of an LTD switch using stainless steel electrodes could exceed 1 million times, provided that the insulation strength of the switch shell doesnt fail.
2014,
26: 085101.
doi: 10.11884/HPLPB201426.085101
Abstract:
It is planned to upgrade the HIRFL-SFC system for improving the quality of extracting beam and making it matched with the separated sector cyclotron (SSC) of the downstream accelerator. The methods mainly include increasing the accelerating voltage of Dee, equipping phase slit or using flattop acceleration system. The flattop acceleration system is a key method to reduce the energy spread and enhance the transmission efficiency. This paper calculates the beam quality of sector-focused cyclotron (SFC) using the cyclotron beam simulation program AGORA and compares the results obtained with and without flattop acceleration system. The results show that the energy spread reduces sharply with flattop system. The beam width in the radial direction and the turn separation meet the requirements of single turn extraction at the entrance of extraction deflector.
It is planned to upgrade the HIRFL-SFC system for improving the quality of extracting beam and making it matched with the separated sector cyclotron (SSC) of the downstream accelerator. The methods mainly include increasing the accelerating voltage of Dee, equipping phase slit or using flattop acceleration system. The flattop acceleration system is a key method to reduce the energy spread and enhance the transmission efficiency. This paper calculates the beam quality of sector-focused cyclotron (SFC) using the cyclotron beam simulation program AGORA and compares the results obtained with and without flattop acceleration system. The results show that the energy spread reduces sharply with flattop system. The beam width in the radial direction and the turn separation meet the requirements of single turn extraction at the entrance of extraction deflector.
2014,
26: 085102.
doi: 10.11884/HPLPB201426.085102
Abstract:
Drift tube linac (DTL) uses the post coupler structure to achieve field stability. In order to explain the mechanism of stability modulation, we explained the structure of the DTL, then, we used the equivalent circuit model to analyse the structure and listed the circuit diagram. At last, we paid attention to the equivalent capacitance which represents the effect between post coupler and drift tube, and made its simulation. The circuit model was used to analyse the disturbed field and provide an explanation of post coupler stabilization. Through comparing the post coupler capacitances from simulation and circuit model, we got the reasonable width of the gap between post coupler and drift tube. Finally, we simulated the disturbed field under different conditions and the circuit theory was confirmed.
Drift tube linac (DTL) uses the post coupler structure to achieve field stability. In order to explain the mechanism of stability modulation, we explained the structure of the DTL, then, we used the equivalent circuit model to analyse the structure and listed the circuit diagram. At last, we paid attention to the equivalent capacitance which represents the effect between post coupler and drift tube, and made its simulation. The circuit model was used to analyse the disturbed field and provide an explanation of post coupler stabilization. Through comparing the post coupler capacitances from simulation and circuit model, we got the reasonable width of the gap between post coupler and drift tube. Finally, we simulated the disturbed field under different conditions and the circuit theory was confirmed.
2014,
26: 085103.
doi: 10.11884/HPLPB201426.085103
Abstract:
Based on the spectrum of turn-by-turn model for the storage ring, spectrum of multi-bunch beam position model was derived through some assumptions. Spectrum of excited electron beam position was analyzed at Shanghai Synchrotron Radiation Facility(SSRF) and Genetic Algorithm was used to fit multi-curve data and the model parameters were obtained. The results show that, after 100 times iteration, all the correlation of fitted data and original data can be up to 95%, and the model can accurately estimate a bimodal split of the spectrum curve. The parameters can be used for monitoring the impedance of the storage ring.
Based on the spectrum of turn-by-turn model for the storage ring, spectrum of multi-bunch beam position model was derived through some assumptions. Spectrum of excited electron beam position was analyzed at Shanghai Synchrotron Radiation Facility(SSRF) and Genetic Algorithm was used to fit multi-curve data and the model parameters were obtained. The results show that, after 100 times iteration, all the correlation of fitted data and original data can be up to 95%, and the model can accurately estimate a bimodal split of the spectrum curve. The parameters can be used for monitoring the impedance of the storage ring.
2014,
26: 085104.
doi: 10.11884/HPLPB201426.085104
Abstract:
Statistic result of experiment data of Qiangguang Ⅰ plasma opening switch (POS) and diode shows that the POS-diode system is not stable. The system instability is induced by the dispersing ejection parameter of the POS plasma source. Plasma source ejection parameter measurement shows that the stability of plasma ejection density as the POS is opening is fine. Range of it is less than 10% but range of the cumulated plasma density in switch zone is more than 100%. POS performance has been obviously influenced by the cumulated plasma density in switch interval and the cathode matter ejection. Calculated result shows that range of the cumulated plasma density change the POS breaking current by more than 200 kA, which is close to the statistic result. Effect of cathode material on the opening performance is notable. Because of it, diode dose might fall 80% with the same breaking current according to MCNP calculation and the experiment result.
Statistic result of experiment data of Qiangguang Ⅰ plasma opening switch (POS) and diode shows that the POS-diode system is not stable. The system instability is induced by the dispersing ejection parameter of the POS plasma source. Plasma source ejection parameter measurement shows that the stability of plasma ejection density as the POS is opening is fine. Range of it is less than 10% but range of the cumulated plasma density in switch zone is more than 100%. POS performance has been obviously influenced by the cumulated plasma density in switch interval and the cathode matter ejection. Calculated result shows that range of the cumulated plasma density change the POS breaking current by more than 200 kA, which is close to the statistic result. Effect of cathode material on the opening performance is notable. Because of it, diode dose might fall 80% with the same breaking current according to MCNP calculation and the experiment result.
2014,
26: 089001.
doi: 10.11884/HPLPB201426.089001
Abstract:
Researches on the laser deposition repairing of TA15 alloy forgings having groove damage were investigated, and the microstructure characteristic of laser deposition repairing component was analyzed. The repaired component experienced a continuous microstructural transition from duplex microstructure with equiaxial and lamellar / in the repaired substrate to the epitaxial coarser columnar with basket weave / through heat-affected zone. And the repaired zone was characterized by a fine / lamellar microstructure with various random orientations, and the was 0.4-0.5 m. It was found that large sloped angle could cause ill bonding along the groove side slope, and a corrective action was given to avoid this defects. The results of the repaired groove sample tensile test at room temperature show that tensile strength is approaching to the forged TA15 alloy, but its impact toughness is a little lower than that of the substrate for its coarser columnar .
Researches on the laser deposition repairing of TA15 alloy forgings having groove damage were investigated, and the microstructure characteristic of laser deposition repairing component was analyzed. The repaired component experienced a continuous microstructural transition from duplex microstructure with equiaxial and lamellar / in the repaired substrate to the epitaxial coarser columnar with basket weave / through heat-affected zone. And the repaired zone was characterized by a fine / lamellar microstructure with various random orientations, and the was 0.4-0.5 m. It was found that large sloped angle could cause ill bonding along the groove side slope, and a corrective action was given to avoid this defects. The results of the repaired groove sample tensile test at room temperature show that tensile strength is approaching to the forged TA15 alloy, but its impact toughness is a little lower than that of the substrate for its coarser columnar .
2014,
26: 089002.
doi: 10.11884/HPLPB201426.089002
Abstract:
It is an important research subject for the optical system of laser display on how to decrease the size of the optical system and improve the lighting effect of the laser source. The optical system design of the laser projector is mainly considered from these two aspects, and it can be found that when the size of the whole fly-eye lens and the focal length of the single fly-eye are certain, more arrays of the fly-eyewill be useful to increase the light effect and decrease the size of the optical engine. The lighting effect of the illumination beams with different numerical apertures and tracing 40 000 light lines of the optimized fly-eye lens show that the transmittance can reach about 92.5% with almost no stray light and scattered light.
It is an important research subject for the optical system of laser display on how to decrease the size of the optical system and improve the lighting effect of the laser source. The optical system design of the laser projector is mainly considered from these two aspects, and it can be found that when the size of the whole fly-eye lens and the focal length of the single fly-eye are certain, more arrays of the fly-eyewill be useful to increase the light effect and decrease the size of the optical engine. The lighting effect of the illumination beams with different numerical apertures and tracing 40 000 light lines of the optimized fly-eye lens show that the transmittance can reach about 92.5% with almost no stray light and scattered light.
2014,
26: 089003.
doi: 10.11884/HPLPB201426.089003
Abstract:
This article studies the preparation of spherical alumina with irregular shape powder by radio frequency (RF) induction plasma. The single factor method is adopted to discuss parameters of spherical alumina prepared by RF plasma process. Studies on the impact on spherical alumina powder of gas flow, negative pressure ventilation, powder feed rate and dispersion methods and other major preparation process parameters are made. Scanning electron microscope (SEM) is used to observe and assess the effect of spheroidization on the bulk density and tapped density. When the alumina is getting through the RF plasma torch in very short time, the particles are heated and melt into droplets. After rapid cooling, spherical solid particles form.
This article studies the preparation of spherical alumina with irregular shape powder by radio frequency (RF) induction plasma. The single factor method is adopted to discuss parameters of spherical alumina prepared by RF plasma process. Studies on the impact on spherical alumina powder of gas flow, negative pressure ventilation, powder feed rate and dispersion methods and other major preparation process parameters are made. Scanning electron microscope (SEM) is used to observe and assess the effect of spheroidization on the bulk density and tapped density. When the alumina is getting through the RF plasma torch in very short time, the particles are heated and melt into droplets. After rapid cooling, spherical solid particles form.
2014,
26: 083002.
doi: 10.11884/HPLPB201426.083002
Abstract:
Response of X-band 4-unit microstrip antenna array to high power electromagnetic pulse is calculated by using the finite difference time domain method and proposed singularity solving technology of conductor edge which maintains high accuracy and computation efficiency. The simulation results show that the maximum response voltage is caused by the superposition of incident pulse in feeding point received by array elements, while the existed mode of wave in the antenna array is different from which motivated in feeding point. Peak response voltage increases as the increase of the angle between incident pulse wave vector and z axis, or the decrease of the angle between incident pulse wave vector in xOy plane projection and x axis. Response spectrum gradually moves to lower frequency band as the increase of the two angles mentioned above.
Response of X-band 4-unit microstrip antenna array to high power electromagnetic pulse is calculated by using the finite difference time domain method and proposed singularity solving technology of conductor edge which maintains high accuracy and computation efficiency. The simulation results show that the maximum response voltage is caused by the superposition of incident pulse in feeding point received by array elements, while the existed mode of wave in the antenna array is different from which motivated in feeding point. Peak response voltage increases as the increase of the angle between incident pulse wave vector and z axis, or the decrease of the angle between incident pulse wave vector in xOy plane projection and x axis. Response spectrum gradually moves to lower frequency band as the increase of the two angles mentioned above.
