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RSS2012 Vol. 24, No. 02
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2012,
24: 253-260.
doi: 10.3788/HPLPB20122402.0253
Abstract:
By using the concept of electromagnetic energy, a systematic description is given for pulsed power generation process. The physical characteristics of energy storage, transmission, and output have been examined with a unified theoretic model. From the characteristic impedance point-of-view, the difference and relation among key pulsed power components have been discussed. According to the theoretical understanding, description and explanation have been given for several typical pulsed power generation schemes, including pulse forming line, pulse compression, and flux compression.
By using the concept of electromagnetic energy, a systematic description is given for pulsed power generation process. The physical characteristics of energy storage, transmission, and output have been examined with a unified theoretic model. From the characteristic impedance point-of-view, the difference and relation among key pulsed power components have been discussed. According to the theoretical understanding, description and explanation have been given for several typical pulsed power generation schemes, including pulse forming line, pulse compression, and flux compression.
2012,
24: 261-266.
Abstract:
KTa1-xNbxO3(KTN) crystal exhibits an extremely large quadratic electro-optic effect, which can manipulate the phase, intensity and propagation direction of the light. KTN devices can be applied not only to optical communications, but also to various other fields that use optical beams, such as displays, medical use. The influence of Ta/Nb fraction, crystal temperature, inclusions and composition variation on the Kerr effect of KTN crystals is discussed in this paper. Several KTN devices based on the Kerr effect, including electro-optic modulator, optical switch, beam scanner, varifocal lens and spectrometer are introduced. The basic principle, research progress and application prospect of the devices are described. The trends in the research and development of the KTN devices is reviewed and predicted.
KTa1-xNbxO3(KTN) crystal exhibits an extremely large quadratic electro-optic effect, which can manipulate the phase, intensity and propagation direction of the light. KTN devices can be applied not only to optical communications, but also to various other fields that use optical beams, such as displays, medical use. The influence of Ta/Nb fraction, crystal temperature, inclusions and composition variation on the Kerr effect of KTN crystals is discussed in this paper. Several KTN devices based on the Kerr effect, including electro-optic modulator, optical switch, beam scanner, varifocal lens and spectrometer are introduced. The basic principle, research progress and application prospect of the devices are described. The trends in the research and development of the KTN devices is reviewed and predicted.
2012,
24: 267-275.
Abstract:
Heat energy loss fraction and corresponding equilibrium temperature of combustor are roughly estimated according to the heat transfer theory on condition that input fuels mass flow rates, compositions proportioning and relevant configuration parameters of combustor are known. Entrance boundary parameters of primary nozzle are then determined. The flow field in coupling region and optical cavity of annular hypersonic low temperature (HYLTE) nozzle is numerically simulated using 3D computational fluid dynamics method. Spatial distributions of F atom mass fraction, static temperature and pressure are described. Small signal gain coefficient distributions for spectral lines in optical cavity are calculated by post processing of the flow field data. The experiments of measuring output spectrum and moving optical axis demonstrate the rationality of the computational model considering heat energy loss of combustor walls.
Heat energy loss fraction and corresponding equilibrium temperature of combustor are roughly estimated according to the heat transfer theory on condition that input fuels mass flow rates, compositions proportioning and relevant configuration parameters of combustor are known. Entrance boundary parameters of primary nozzle are then determined. The flow field in coupling region and optical cavity of annular hypersonic low temperature (HYLTE) nozzle is numerically simulated using 3D computational fluid dynamics method. Spatial distributions of F atom mass fraction, static temperature and pressure are described. Small signal gain coefficient distributions for spectral lines in optical cavity are calculated by post processing of the flow field data. The experiments of measuring output spectrum and moving optical axis demonstrate the rationality of the computational model considering heat energy loss of combustor walls.
2012,
24: 276-280.
Abstract:
Based on the extended Huygens-Fresnel principle, the expression for the mean-squared width of apertured polychromatic Gaussian Schell-model (GSM) beams propagating through atmospheric turbulence is derived by using the quadratic approximation of Rytovs phase structure function and the method of the window function being expanded into a finite sum of complex-valued Gaussian functions. It is shown that the mean squared beam width of apertured polychromatic GSM beam increases with increasing the refractive index structure constant, the beam bandwidth and the propagation distance, and with decreasing the beam truncation parameter and the beam coherence parameter. Furthermore, apertured polychromatic GSM beams with larger bandwidth, smaller beam truncation parameter, and smaller beam coherence parameter are less affected by the turbulence.
Based on the extended Huygens-Fresnel principle, the expression for the mean-squared width of apertured polychromatic Gaussian Schell-model (GSM) beams propagating through atmospheric turbulence is derived by using the quadratic approximation of Rytovs phase structure function and the method of the window function being expanded into a finite sum of complex-valued Gaussian functions. It is shown that the mean squared beam width of apertured polychromatic GSM beam increases with increasing the refractive index structure constant, the beam bandwidth and the propagation distance, and with decreasing the beam truncation parameter and the beam coherence parameter. Furthermore, apertured polychromatic GSM beams with larger bandwidth, smaller beam truncation parameter, and smaller beam coherence parameter are less affected by the turbulence.
2012,
24: 281-284.
Abstract:
The orbital change of space debris using laser irradiation was analyzed to study the laser removal processes of centimeter-scale space debris. A physical model was build up, and the space debris re-entering and burnout processes were studied numerically. The results indicate that in order to remove the debris of centimeter scale, the included angle between the direction of velocity and the velocity increment must be larger than 90, and the laser power should be up to 100 kW.
The orbital change of space debris using laser irradiation was analyzed to study the laser removal processes of centimeter-scale space debris. A physical model was build up, and the space debris re-entering and burnout processes were studied numerically. The results indicate that in order to remove the debris of centimeter scale, the included angle between the direction of velocity and the velocity increment must be larger than 90, and the laser power should be up to 100 kW.
2012,
24: 285-288.
Abstract:
The fundamental equations of Fourier heat transfer model and non-Fourier heat transfer model were numerically solved, with the finite difference method. The relative changes between temperature curves of the two heat transfer models were analyzed under laser irradiation with different pulse widths of 10 ns, 1 ns, 100 ps, 10 ps. The impact of different thermal relaxation time on non-Fourier model results was discussed. For pulses of pulse width less than or equal to 100 ps irradiating silicon material, the surface temperature increases slowly and carrier effect happens, which the non-Fourier model can reflect properly. As for general material, when the pulse width is less than or equal to the thermal relaxation time of material, carrier effect occurs. In this case, the non-Fourier model should be used.
The fundamental equations of Fourier heat transfer model and non-Fourier heat transfer model were numerically solved, with the finite difference method. The relative changes between temperature curves of the two heat transfer models were analyzed under laser irradiation with different pulse widths of 10 ns, 1 ns, 100 ps, 10 ps. The impact of different thermal relaxation time on non-Fourier model results was discussed. For pulses of pulse width less than or equal to 100 ps irradiating silicon material, the surface temperature increases slowly and carrier effect happens, which the non-Fourier model can reflect properly. As for general material, when the pulse width is less than or equal to the thermal relaxation time of material, carrier effect occurs. In this case, the non-Fourier model should be used.
2012,
24: 289-292.
doi: 10.3788/HPLPB20122402.0289
Abstract:
A method of scanning filtering for improving the signal to noise ratio (SNR) of chirped pulse has been proposed. The method is based on Fabry Perot (F-P) etalon with electro optic crystal, and uses the principle of multi beam interference of the F-P etalon and the linear electro optic effect of the crystal. The time varying function of the voltage applied on electro optic crystal was given, and the main factors affecting the SNR were analyzed. Moreover, the effects of the control parameters of the applied voltage on the SNR and the transmittance of the filter were discussed. The results show that the SNR of chirped pulse laser can be improved nearly two orders of magnitude by using the scanning filtering method.
A method of scanning filtering for improving the signal to noise ratio (SNR) of chirped pulse has been proposed. The method is based on Fabry Perot (F-P) etalon with electro optic crystal, and uses the principle of multi beam interference of the F-P etalon and the linear electro optic effect of the crystal. The time varying function of the voltage applied on electro optic crystal was given, and the main factors affecting the SNR were analyzed. Moreover, the effects of the control parameters of the applied voltage on the SNR and the transmittance of the filter were discussed. The results show that the SNR of chirped pulse laser can be improved nearly two orders of magnitude by using the scanning filtering method.
2012,
24: 293-296.
Abstract:
Based on the generalized Huygens-Fresnel integral and the Hermite-Gaussian expansion of a Lorentz function, an analytical propagation expression for the kurtosis parameter of a partially coherent Lorentz-Gauss beam through a paraxial ABCD optical system has been derived in turbulent atmosphere, and the kurtosis parameter was numerically calculated. The results show that the influences of the spatial coherence length and the structure constant of the atmospheric turbulence on the kurtosis parameter are related to the beam parameters. When the spatial coherence length is smaller than the beam parameters, the influence of the spatial coherence length is remarkable. When the beam parameter of the Lorentzian part is relatively large or the beam parameter of the Gaussian part is relatively small, the influence of the structure constant is distinct. Moreover, the influence of the structure constant augments with increasing the propagation distance.
Based on the generalized Huygens-Fresnel integral and the Hermite-Gaussian expansion of a Lorentz function, an analytical propagation expression for the kurtosis parameter of a partially coherent Lorentz-Gauss beam through a paraxial ABCD optical system has been derived in turbulent atmosphere, and the kurtosis parameter was numerically calculated. The results show that the influences of the spatial coherence length and the structure constant of the atmospheric turbulence on the kurtosis parameter are related to the beam parameters. When the spatial coherence length is smaller than the beam parameters, the influence of the spatial coherence length is remarkable. When the beam parameter of the Lorentzian part is relatively large or the beam parameter of the Gaussian part is relatively small, the influence of the structure constant is distinct. Moreover, the influence of the structure constant augments with increasing the propagation distance.
2012,
24: 297-300.
Abstract:
Digital monitoring for length variation of optical fibers in femtosecond timing and synchronization system of XFEL Abstract:The requirements for the femtosecond timing and synchronization (fs TS) system in an X-ray free electron laser (XFEL) facility are analyzed. The timing/phase distribution method using optical fiber is adopted. Since the optical length of the fiber changes as the temperature drifts, the influence of temperature drift on the length variation of the fiber is studied in comparative experiments. An FPGA-based digital phase/amplitude detector is designed to record the data of the length variation. For a 100-meter-long fiber, the timing drift caused by length variation is 6 ps (peak-peak value) over 24 hours. The result shows the digital phase/amplitude detector could be used for length variation monitoring and stabilization of the fs TS system.
Digital monitoring for length variation of optical fibers in femtosecond timing and synchronization system of XFEL Abstract:The requirements for the femtosecond timing and synchronization (fs TS) system in an X-ray free electron laser (XFEL) facility are analyzed. The timing/phase distribution method using optical fiber is adopted. Since the optical length of the fiber changes as the temperature drifts, the influence of temperature drift on the length variation of the fiber is studied in comparative experiments. An FPGA-based digital phase/amplitude detector is designed to record the data of the length variation. For a 100-meter-long fiber, the timing drift caused by length variation is 6 ps (peak-peak value) over 24 hours. The result shows the digital phase/amplitude detector could be used for length variation monitoring and stabilization of the fs TS system.
2012,
24: 301-306.
Abstract:
For reducing the effect of undulate background in dim infrared targets detection, an anisotropic method is presented for infrared background prediction. According to differences of local gradient character among target region, smooth background region and undulate background region, the edge stopping function of anisotropic partial differential equations is improved to an increasing function with the value of the direction grads. Then the mean of the two least values of the edge stopping function is derived as the prediction value of the background. Simulation results show that the method selectively retains the smooth background region and the undulate background region, and achieves good prediction of background.
For reducing the effect of undulate background in dim infrared targets detection, an anisotropic method is presented for infrared background prediction. According to differences of local gradient character among target region, smooth background region and undulate background region, the edge stopping function of anisotropic partial differential equations is improved to an increasing function with the value of the direction grads. Then the mean of the two least values of the edge stopping function is derived as the prediction value of the background. Simulation results show that the method selectively retains the smooth background region and the undulate background region, and achieves good prediction of background.
2012,
24: 307-311.
doi: 10.3788/HPLPB20122402.0307
Abstract:
The paper presents an inversion algorithm for laser diode ceilometer to retrieve the vertical visibility. According to the working principle of laser ceilometer, a method has been derived for determining the boundary value of the aerosol extinction coefficient in the lower troposphere from the elastic scattering lidar equation. Then the vertical distribution of the extinction coefficient can be retrieved by Fernald method, according to which the average visibility can be further retrieved in the vertical direction. The algorithm retrieves the vertical visibility from actual measurement data of ceilometer. The result comparison with Vaisala ceilometer shows that, the algorithm retrieves the vertical visibility more accurately and reliably.
The paper presents an inversion algorithm for laser diode ceilometer to retrieve the vertical visibility. According to the working principle of laser ceilometer, a method has been derived for determining the boundary value of the aerosol extinction coefficient in the lower troposphere from the elastic scattering lidar equation. Then the vertical distribution of the extinction coefficient can be retrieved by Fernald method, according to which the average visibility can be further retrieved in the vertical direction. The algorithm retrieves the vertical visibility from actual measurement data of ceilometer. The result comparison with Vaisala ceilometer shows that, the algorithm retrieves the vertical visibility more accurately and reliably.
2012,
24: 312-314.
doi: 10.3788/HPLPB20122402.0312
Abstract:
An electro-optical switch based on Fabry-Perot(F-P) etalon is proposed. The working principle of the F-P switch is introduced, and the structure of the F-P switch is designed. As an example, the dependences of transmittance of the F-P switch on driving voltage and wavelength are analyzed with lithium niobate crystal as the intracavity medium. The results indicate that, with the same crystal parameters, the driving voltage can be dramatically reduced for the F-P switch compared with those switches using orthogonal polarizers, and mode selection can also be achieved in this F-P switch.
An electro-optical switch based on Fabry-Perot(F-P) etalon is proposed. The working principle of the F-P switch is introduced, and the structure of the F-P switch is designed. As an example, the dependences of transmittance of the F-P switch on driving voltage and wavelength are analyzed with lithium niobate crystal as the intracavity medium. The results indicate that, with the same crystal parameters, the driving voltage can be dramatically reduced for the F-P switch compared with those switches using orthogonal polarizers, and mode selection can also be achieved in this F-P switch.
2012,
24: 315-320.
doi: 10.3788/HPLPB20122402.0315
Abstract:
A novel and rapidly tunable laser was proposed, consisting of a semiconductor ring laser (SRL) formed by an active microring under constant current pumping and a monolithically integrated external tunable passive microring reflector. The geometry, therefore, enables very fast tuning by separating the mechanism (the active microring cavity) that defines stable lasing mode frequencies from the tuning mechanism (the passive microring) that only selects one of these stable frequencies. Furthermore, compared to the laser based on grating structures, this SRL offers many promising advantages including strong mode-selection and simple fabrication, which does not require phase matching sections and provides a strong immunity of the output wavelength to the thermal fluctuations of the tunable section. Theoretical simulations based on a multimode rate-equation model were used to study the performance of the laser. Numerical simulations demonstrate digital tuning of the laser across 15 cavity modes with reasonably low threshold current of about 40 mA and moderate side-mode suppression ratio (SMSR).
A novel and rapidly tunable laser was proposed, consisting of a semiconductor ring laser (SRL) formed by an active microring under constant current pumping and a monolithically integrated external tunable passive microring reflector. The geometry, therefore, enables very fast tuning by separating the mechanism (the active microring cavity) that defines stable lasing mode frequencies from the tuning mechanism (the passive microring) that only selects one of these stable frequencies. Furthermore, compared to the laser based on grating structures, this SRL offers many promising advantages including strong mode-selection and simple fabrication, which does not require phase matching sections and provides a strong immunity of the output wavelength to the thermal fluctuations of the tunable section. Theoretical simulations based on a multimode rate-equation model were used to study the performance of the laser. Numerical simulations demonstrate digital tuning of the laser across 15 cavity modes with reasonably low threshold current of about 40 mA and moderate side-mode suppression ratio (SMSR).
2012,
24: 321-326.
doi: 10.3788/HPLPB20122402.0321
Abstract:
A fast active contour tracking(ACT) algorithm based on log-likelihood image segmentation has been proposed to solve the scale change problem in the process of target tracking. The algorithm adopts the log-likelihood image segmentation method, which segments images according to their log-likelihood images built based on the color difference between target and background, and the mathematical morphology method, and tracks the target with conventional ACT algorithm combined with Kalman filter. It tracks the target precisely with distinct contour features and stable tracking performance, and can well adapt to the target scale change. The Kalman filter adopted reduces the number of iterations for algorithm convergence through its forecast of the target position, and thus the fast ACT algorithm is about 33% more efficient than the conventional one.
A fast active contour tracking(ACT) algorithm based on log-likelihood image segmentation has been proposed to solve the scale change problem in the process of target tracking. The algorithm adopts the log-likelihood image segmentation method, which segments images according to their log-likelihood images built based on the color difference between target and background, and the mathematical morphology method, and tracks the target with conventional ACT algorithm combined with Kalman filter. It tracks the target precisely with distinct contour features and stable tracking performance, and can well adapt to the target scale change. The Kalman filter adopted reduces the number of iterations for algorithm convergence through its forecast of the target position, and thus the fast ACT algorithm is about 33% more efficient than the conventional one.
2012,
24: 327-330.
doi: 10.3788/HPLPB20122402.0327
Abstract:
An anomaly detection algorithm for hyperspectral images based on multiscale decomposition is proposed. Both spatial and spectral information is used to locate and detect targets under the condition of no prior knowledge about target and background. Firstly, the hyperspectral images are decomposed into a series of different scaled sub-bands using nonsubsampled pyramid decomposition. Then using the correlation of neighborhood coefficient of different scaled space in a hyperspectral band, the background data is optimally predicted by reducing the anomalous data using unsharped masking filter in different scale of each band and finally the anomaly targets can be detected by using designed kernel RX operator in the feature space. Numerical experiments have been conducted on real and synthesized AVIRIS data to validate the effectiveness of the proposed algorithm. Compared with classical RX algorithm, the proposed algorithm has better detection performance and lower false alarm probability.
An anomaly detection algorithm for hyperspectral images based on multiscale decomposition is proposed. Both spatial and spectral information is used to locate and detect targets under the condition of no prior knowledge about target and background. Firstly, the hyperspectral images are decomposed into a series of different scaled sub-bands using nonsubsampled pyramid decomposition. Then using the correlation of neighborhood coefficient of different scaled space in a hyperspectral band, the background data is optimally predicted by reducing the anomalous data using unsharped masking filter in different scale of each band and finally the anomaly targets can be detected by using designed kernel RX operator in the feature space. Numerical experiments have been conducted on real and synthesized AVIRIS data to validate the effectiveness of the proposed algorithm. Compared with classical RX algorithm, the proposed algorithm has better detection performance and lower false alarm probability.
2012,
24: 331-337.
doi: 10.3788/HPLPB20122402.0331
Abstract:
Dynamic speckles appear when a cylinder rotating with a constant angular velocity is irradiated by a Gaussian light beam. The statistical property of dynamic speckles in far-field diffraction is acquired when the irradiated area is larger than the cylinder surface. The normalized space-time cross-correlation of dynamic speckle intensity fluctuations is obtained with different cylinder radii in different incidence conditions. The results show that the correlation is improved when the cylinder radius and rotating speed decrease. When the cylinder rotates at a constant speed, the peak value of cross-correlation function descends gradually as the distance between the two observation points increases, whereas the peak position increases. In the case of approximate point irradiation, the spatial correlation length is almost unchanged and the correlation time extends obviously as the cylinder radius increases.
Dynamic speckles appear when a cylinder rotating with a constant angular velocity is irradiated by a Gaussian light beam. The statistical property of dynamic speckles in far-field diffraction is acquired when the irradiated area is larger than the cylinder surface. The normalized space-time cross-correlation of dynamic speckle intensity fluctuations is obtained with different cylinder radii in different incidence conditions. The results show that the correlation is improved when the cylinder radius and rotating speed decrease. When the cylinder rotates at a constant speed, the peak value of cross-correlation function descends gradually as the distance between the two observation points increases, whereas the peak position increases. In the case of approximate point irradiation, the spatial correlation length is almost unchanged and the correlation time extends obviously as the cylinder radius increases.
2012,
24: 338-342.
doi: 10.3788/HPLPB20122402.0338
Abstract:
Ta2O5 aerogels are prepared by sol-gel technique in the presence of different kinds of acid catalysts such as HCI,HNO3 and H2SO4. The gelation time of H2SO4 system is far less than that of HCI and HNO3 systems. Moreover, the shrinkage and cracking phenomena of Ta2O5 gels in solvent exchnging process and supercritical drying process, which are unavoidable in HCI and HNO3 systems, are obviously inhibited in H2SO4 system. The SEM observations find that the particles of Ta2O5 aerogels catalyzed by H2SO4 are much bigger due to the cluster effect of nano-particles. The BET analysis finds that Ta2O5 aerogels catalyzed by H2SO4 exhibit the BJH surface area of 167 m2/g, which is much lower due to the cluster phenomenon. XPS estimating results reveal that all the S but no CI or N elements remain in Ta2O5 aerogels, indicating that S element is in the Ta-O-Ta crosslinking structure. Due to this particular structure, the shrinkage and cracking phenomena of Ta2O5 aerogels are significantly prevented, and better mechanical properties are achieved.
Ta2O5 aerogels are prepared by sol-gel technique in the presence of different kinds of acid catalysts such as HCI,HNO3 and H2SO4. The gelation time of H2SO4 system is far less than that of HCI and HNO3 systems. Moreover, the shrinkage and cracking phenomena of Ta2O5 gels in solvent exchnging process and supercritical drying process, which are unavoidable in HCI and HNO3 systems, are obviously inhibited in H2SO4 system. The SEM observations find that the particles of Ta2O5 aerogels catalyzed by H2SO4 are much bigger due to the cluster effect of nano-particles. The BET analysis finds that Ta2O5 aerogels catalyzed by H2SO4 exhibit the BJH surface area of 167 m2/g, which is much lower due to the cluster phenomenon. XPS estimating results reveal that all the S but no CI or N elements remain in Ta2O5 aerogels, indicating that S element is in the Ta-O-Ta crosslinking structure. Due to this particular structure, the shrinkage and cracking phenomena of Ta2O5 aerogels are significantly prevented, and better mechanical properties are achieved.
2012,
24: 343-348.
doi: 10.3788/HPLPB20122402.0343
Abstract:
Considering the additional surface variation of large-aperture thin KDP crystal placed with the departure angle of 45 from the horizontal plane in inertial confinement fusion (ICF) systems, which caused by the fabrication errors of KDP crystal and its mounting system, a finite element analysis model has been built up for the KDP crystal based on the experimental measurement data of surface profile and its mounting system with fabrication errors of different types and sizes. The influence of the fabrication errors of KDP crystal and its mounting system on the additional surface variation of KDP crystal has been simulated and the P-V and RMS values of the crystal surface profiles have been given. It is shown that the fabrication error of the edges of KDP crystal and the concave fabrication error of support surface of mounting system are important reasons for relatively large additional surface variation, and the fabrication error of KDP crystal leads to nonuniform deformation. Whereas the convex and wavy fabrication errors of support surface and the random fabrication error of strip surface of the mounting system lead to relatively small additional surface variation. The additional surface variation caused by the random fabrication error of support surface is in between.
Considering the additional surface variation of large-aperture thin KDP crystal placed with the departure angle of 45 from the horizontal plane in inertial confinement fusion (ICF) systems, which caused by the fabrication errors of KDP crystal and its mounting system, a finite element analysis model has been built up for the KDP crystal based on the experimental measurement data of surface profile and its mounting system with fabrication errors of different types and sizes. The influence of the fabrication errors of KDP crystal and its mounting system on the additional surface variation of KDP crystal has been simulated and the P-V and RMS values of the crystal surface profiles have been given. It is shown that the fabrication error of the edges of KDP crystal and the concave fabrication error of support surface of mounting system are important reasons for relatively large additional surface variation, and the fabrication error of KDP crystal leads to nonuniform deformation. Whereas the convex and wavy fabrication errors of support surface and the random fabrication error of strip surface of the mounting system lead to relatively small additional surface variation. The additional surface variation caused by the random fabrication error of support surface is in between.
2012,
24: 349-352.
doi: 10.3788/HPLPB20122402.0349
Abstract:
High-stable and monodisperse colloidal nano-silver particles were synthesized by reduction of ［Ag(NH3)2］+ with hydrazine hydrate using sodium citrate as stabilizer and polyvinylpyrrolidone(PVP) as dispersant. Furthermore, nano-silver/polystyrene composite was prepared via microemulsion polymerization.The optical properties of the nano-silver particles were studied by ultraviolet-visible (UV-Vis) absorption spectra, and the crystal structure and microscopic morphology were characterized via X-ray diffraction(XRD) and transmission electron microscopy(TEM), respectively. Results show that, the nano-silver particles belong to cubic crystal system and have an average diameter of 10 nm without aggregation and oxidation, and their crystal structure and microscopic morphology do not change obviously during the process of polymerization. Gel permeation chromatography(GPC) data shows that the weight-average molecular weight of polystyrene matrix is over 4.03106, and the molecular weight distribution index is 1.21. Thermal gravity-differential scanning calorimetry(TG-DSC) test demonstrates that the nano-silver/polystyrene composite has excellent thermal stability.
High-stable and monodisperse colloidal nano-silver particles were synthesized by reduction of ［Ag(NH3)2］+ with hydrazine hydrate using sodium citrate as stabilizer and polyvinylpyrrolidone(PVP) as dispersant. Furthermore, nano-silver/polystyrene composite was prepared via microemulsion polymerization.The optical properties of the nano-silver particles were studied by ultraviolet-visible (UV-Vis) absorption spectra, and the crystal structure and microscopic morphology were characterized via X-ray diffraction(XRD) and transmission electron microscopy(TEM), respectively. Results show that, the nano-silver particles belong to cubic crystal system and have an average diameter of 10 nm without aggregation and oxidation, and their crystal structure and microscopic morphology do not change obviously during the process of polymerization. Gel permeation chromatography(GPC) data shows that the weight-average molecular weight of polystyrene matrix is over 4.03106, and the molecular weight distribution index is 1.21. Thermal gravity-differential scanning calorimetry(TG-DSC) test demonstrates that the nano-silver/polystyrene composite has excellent thermal stability.
2012,
24: 353-356.
doi: 10.3788/HPLPB20122402.0353
Abstract:
The polystyrene(PS) microspheres were coated by gold colloid with an average grain size of 4.6 nm by the electrostatic effect, and then electroless plated with gold silver consecutively. The deposited gold layer was 70 to 90 nm thick, almost coating the PS spheres completely. The silver particles deposited subsequently were compact, and larger than the previously deposited gold particles, forming a 200 to 400 nm-thick layer on the surface of each Au/PS microsphere. The self-supported hollow-sphere Au40Ag60 alloy was then obtained after the template being removed. Finally, the columniform foamed Au-Ag alloy, 5 mm in diameter, 1.2 g/cm3 in density, was obtained with thehollow spheres of 10 m diameter after heat treatment.
The polystyrene(PS) microspheres were coated by gold colloid with an average grain size of 4.6 nm by the electrostatic effect, and then electroless plated with gold silver consecutively. The deposited gold layer was 70 to 90 nm thick, almost coating the PS spheres completely. The silver particles deposited subsequently were compact, and larger than the previously deposited gold particles, forming a 200 to 400 nm-thick layer on the surface of each Au/PS microsphere. The self-supported hollow-sphere Au40Ag60 alloy was then obtained after the template being removed. Finally, the columniform foamed Au-Ag alloy, 5 mm in diameter, 1.2 g/cm3 in density, was obtained with thehollow spheres of 10 m diameter after heat treatment.
2012,
24: 0357-360.
doi: 10.3788/HPLPB20122402.0357
Abstract:
Based on the self-focusing and uniform dispersion principle, a spectrograph with uniform dispersion bent crystal was developed for Z-pinch plasma X-ray diagnosis. -quartz (1010) crystal was used as dispersion element and the Bragg angle of the crystal analyzer ranged from 43.4 to 72.7. The X-ray film was employed to receive the spectra with an effective area of 10 mm50 mm. The experiment was carried out at the Yang accelerator in China Academy of Engineering Physics. The H-like and He-like spectra of aluminum Z-pinch plasma were obtained. The distribution of aluminum spectra satisfies the uniform dispersion condition. The linear dispersion of the developed spectrograph is -116.198 mm/nm and the error is only 3.168% relative to the theoretical value of -120 mm/nm. The experimental results demonstrate that the uniform dispersion bent crystal spectrograph is suitable for Z-pinch plasma X-ray spectroscopy diagnosis.
Based on the self-focusing and uniform dispersion principle, a spectrograph with uniform dispersion bent crystal was developed for Z-pinch plasma X-ray diagnosis. -quartz (1010) crystal was used as dispersion element and the Bragg angle of the crystal analyzer ranged from 43.4 to 72.7. The X-ray film was employed to receive the spectra with an effective area of 10 mm50 mm. The experiment was carried out at the Yang accelerator in China Academy of Engineering Physics. The H-like and He-like spectra of aluminum Z-pinch plasma were obtained. The distribution of aluminum spectra satisfies the uniform dispersion condition. The linear dispersion of the developed spectrograph is -116.198 mm/nm and the error is only 3.168% relative to the theoretical value of -120 mm/nm. The experimental results demonstrate that the uniform dispersion bent crystal spectrograph is suitable for Z-pinch plasma X-ray spectroscopy diagnosis.
2012,
24: 361-365.
doi: 10.3788/HPLPB20122402.0361
Abstract:
Hollow polymer microspheres about 5 m in diameter were synthesized by dynamic swelling method using micron-sized polystyrene spheres with positive charges on surfaces as seeds. The synthesis process included swelling by organic solvents such as toluene and divinylbenzene, polymerizing and coating. The influences of variety and dosage of organic solvents on diameter, size distribution and hole structure of hollow microspheres were investigated, and the formation mechanism of hollow microspheres was discussed. It is indicated that some volatile organic solvents, such as toluene and dimethylbenzene, are crucial to hollow structure formation. Experimental results show that, more toluene leads to larger hollow structure after swelling, and dimethylbenzene is good for hollow structure formation, owing to its low solubility.
Hollow polymer microspheres about 5 m in diameter were synthesized by dynamic swelling method using micron-sized polystyrene spheres with positive charges on surfaces as seeds. The synthesis process included swelling by organic solvents such as toluene and divinylbenzene, polymerizing and coating. The influences of variety and dosage of organic solvents on diameter, size distribution and hole structure of hollow microspheres were investigated, and the formation mechanism of hollow microspheres was discussed. It is indicated that some volatile organic solvents, such as toluene and dimethylbenzene, are crucial to hollow structure formation. Experimental results show that, more toluene leads to larger hollow structure after swelling, and dimethylbenzene is good for hollow structure formation, owing to its low solubility.
2012,
24: 365-369.
doi: 10.3788/HPLPB20122402.0365
Abstract:
The technology for coating the telescope primary mirror with protected aluminium layer is studied during the preparative process, when the mirror is face up. According to the geometry of ZZS3200 large coating equipment, the traditionally calculative model is modified, and the uniformity of the aluminium and dielectric layers is analyzed separately. The simulated results accord with the experimental results, and in the 2.4 m diameter range, the non-uniformity of the whole film is within 5.5%. The 1.8 m-diameter plane reflective primary mirror has been prepared with optimized technical parameters. Its reflectance after coating is 88.6% in the wavelength range from 350 to 1 800 nm. Furthermore, the films have passed the environment stability test successfully.
The technology for coating the telescope primary mirror with protected aluminium layer is studied during the preparative process, when the mirror is face up. According to the geometry of ZZS3200 large coating equipment, the traditionally calculative model is modified, and the uniformity of the aluminium and dielectric layers is analyzed separately. The simulated results accord with the experimental results, and in the 2.4 m diameter range, the non-uniformity of the whole film is within 5.5%. The 1.8 m-diameter plane reflective primary mirror has been prepared with optimized technical parameters. Its reflectance after coating is 88.6% in the wavelength range from 350 to 1 800 nm. Furthermore, the films have passed the environment stability test successfully.
2012,
24: 370-374.
doi: 10.3788/HPLPB20122402.0370
Abstract:
Carbon aerogels(CAs) and activated CAs doped with surfactant P123(PEO-PPO-PEO, molecular weight: 5 800) were prepared by conventional drying. SEM images show a handsome network structure of CAs prepared by conventional drying, and the network structure becomes more compact after activation. FTIR spectra show that there is strong interaction between P123 and RF (resorcinol-formaldehyde), and P123 disappears after carbonization. TG and DTG curve analyses indicate that the P123 is not a kind of impurity for it decomposes completely after carbonization at 440 ℃. Characterized by nitrogen adsorption, CAs prepared by conventional drying have a high specific surface area of 570 m2g-1, which is up to about 3 500 m2g-1 after activation.
Carbon aerogels(CAs) and activated CAs doped with surfactant P123(PEO-PPO-PEO, molecular weight: 5 800) were prepared by conventional drying. SEM images show a handsome network structure of CAs prepared by conventional drying, and the network structure becomes more compact after activation. FTIR spectra show that there is strong interaction between P123 and RF (resorcinol-formaldehyde), and P123 disappears after carbonization. TG and DTG curve analyses indicate that the P123 is not a kind of impurity for it decomposes completely after carbonization at 440 ℃. Characterized by nitrogen adsorption, CAs prepared by conventional drying have a high specific surface area of 570 m2g-1, which is up to about 3 500 m2g-1 after activation.
2012,
24: 375-378.
doi: 10.3788/HPLPB20122402.0375
Abstract:
Deuterated poly(vincylcyclohexane) (D-PVCH, C8H8D6) was successfully prepared via deuterated catalytic technology of polystyrene(PS). The structure of D-PVCH was characterized by FT-IR and 1HNMR spectroscopy, and the results show good agreement with the proposed structure and the deuterated ratio is 41.5%. DSC and TG analyses of the D-PVCH show that D-PVCH possesses good thermal stability (glass transition temperature of 125 ℃, 5% weight loss temperature of 403 ℃). Additionally, D-PVCH dissolves in common solvents such as petroleum ether, cyclohexane and toluene at room temperature. Compared with PS, D-PVCH possesses better thermal stability and improved solubility.
Deuterated poly(vincylcyclohexane) (D-PVCH, C8H8D6) was successfully prepared via deuterated catalytic technology of polystyrene(PS). The structure of D-PVCH was characterized by FT-IR and 1HNMR spectroscopy, and the results show good agreement with the proposed structure and the deuterated ratio is 41.5%. DSC and TG analyses of the D-PVCH show that D-PVCH possesses good thermal stability (glass transition temperature of 125 ℃, 5% weight loss temperature of 403 ℃). Additionally, D-PVCH dissolves in common solvents such as petroleum ether, cyclohexane and toluene at room temperature. Compared with PS, D-PVCH possesses better thermal stability and improved solubility.
2012,
24: 379-382.
doi: 10.3788/HPLPB20122402.0379
Abstract:
Organic aerogels were fabricated by sol-gel polymerization of melamine and formaldehyde monomers. The porous morphology, structure and thermal stability of the aerogels were characterized by nitrogen adsorption, Fourier transform infrared spectroscopy(FTIR) and thermogravimetry-mass spectrometry(TG-MS). The results show that melamine(M)-formaldehyde(F) aerogel is a material of continuous, interpenetrant, three-dimensional network structure with a high surface area, whose corresponding specific surface is roughly 842 m2/g, and average pore size is 16.04 nm. The pyrolysis process releases several gaseous products, including NO, H2O, NH3, NO2, CO2 and CH4, which is conformed with TG curves, and nearly 97% of MF is decomposed in all. The aerogel is expected to be employed as the template to obtain three-dimensional nanoporous materials.
Organic aerogels were fabricated by sol-gel polymerization of melamine and formaldehyde monomers. The porous morphology, structure and thermal stability of the aerogels were characterized by nitrogen adsorption, Fourier transform infrared spectroscopy(FTIR) and thermogravimetry-mass spectrometry(TG-MS). The results show that melamine(M)-formaldehyde(F) aerogel is a material of continuous, interpenetrant, three-dimensional network structure with a high surface area, whose corresponding specific surface is roughly 842 m2/g, and average pore size is 16.04 nm. The pyrolysis process releases several gaseous products, including NO, H2O, NH3, NO2, CO2 and CH4, which is conformed with TG curves, and nearly 97% of MF is decomposed in all. The aerogel is expected to be employed as the template to obtain three-dimensional nanoporous materials.
2012,
24: 383-388.
doi: 10.3788/HPLPB20122402.0383
Abstract:
The Mortar spectral element method and message passing interface(MPI) parallel computation technique have been used in studying turbulent mixing of Kelvin-Helmhtz instabilities, and the evolution mechanism of Kelvin-Helmhtz instabilities has been estimated with the calculation of momentum thickness, energy spectrum and total kinetic energy. The results show that, the three-dimensional Mortar spectral element method can effectively capture the turbulent mixing of Kelvin-Helmhtz instability, with cascading and combination of turbulent eddies clearly shown. In addition, the initial laminar fluid flow of Kelvin-Helmhtz instability gradually developed into a turbulent flow with continuous spectrum structure in the simulation, thus two-dimensional to three-dimensional transition can be achieved. The statistical turbulent kinetic energy reflects the viscous dissipation of the turbulent mixing. The validity of the spectral element code has been demonstrated, and the feasibility of the spectral element method in turbulent study has been proved.
The Mortar spectral element method and message passing interface(MPI) parallel computation technique have been used in studying turbulent mixing of Kelvin-Helmhtz instabilities, and the evolution mechanism of Kelvin-Helmhtz instabilities has been estimated with the calculation of momentum thickness, energy spectrum and total kinetic energy. The results show that, the three-dimensional Mortar spectral element method can effectively capture the turbulent mixing of Kelvin-Helmhtz instability, with cascading and combination of turbulent eddies clearly shown. In addition, the initial laminar fluid flow of Kelvin-Helmhtz instability gradually developed into a turbulent flow with continuous spectrum structure in the simulation, thus two-dimensional to three-dimensional transition can be achieved. The statistical turbulent kinetic energy reflects the viscous dissipation of the turbulent mixing. The validity of the spectral element code has been demonstrated, and the feasibility of the spectral element method in turbulent study has been proved.
2012,
24: 389-393.
doi: 10.3788/HPLPB20122402.0389
Abstract:
W1/O/W2 double emulsion particles of around 2 mm diameter were prepared using emulsion microencapsulation method. The stability of the particles was studied under the quasi-static condition and the rotating flow field, respectively, with the variation of the organic phase concentration and the water-soluble polymer concentration. The enhancement mechanism of the kinetic stability of the particles was explored based on force analysis and deformation analysis. The results show that, both under the quasi-static condition and the rotating flow field, the stability of W1/O/W2 double emulsion particles increases with the increase of PS concentration. However, it increases firstly and then decreases when PVA concentration increases. Moreover, in some conditions, the kinetic stability of W1/O/W2 double emulsion particles is greatly enhanced in the rotating flow field compared with under the quasi-static condition.
W1/O/W2 double emulsion particles of around 2 mm diameter were prepared using emulsion microencapsulation method. The stability of the particles was studied under the quasi-static condition and the rotating flow field, respectively, with the variation of the organic phase concentration and the water-soluble polymer concentration. The enhancement mechanism of the kinetic stability of the particles was explored based on force analysis and deformation analysis. The results show that, both under the quasi-static condition and the rotating flow field, the stability of W1/O/W2 double emulsion particles increases with the increase of PS concentration. However, it increases firstly and then decreases when PVA concentration increases. Moreover, in some conditions, the kinetic stability of W1/O/W2 double emulsion particles is greatly enhanced in the rotating flow field compared with under the quasi-static condition.
2012,
24: 394-398.
doi: 10.3788/HPLPB20122402.0394
Abstract:
The paper proposes a method using chirp-matching optical parametric chirped pulse amplification (OPCPA) scheme to eliminate the pre-pulse within the gain time window defined by the pump duration is proposed. The effects of the pump pulse shape, as well as the delay time between main pulse and pre-pulse on the improvement of signal-to-noise ratio are analyzed. using numerical simulation Comparing the chirp-matching OPCPA scheme with the conventional noncollinear OPCPA scheme, it is shown that the chirp-matching OPCPA scheme can eliminate a pre-pulse which is much closer to the main pulse, and it depends less on the pump pulse shape.
The paper proposes a method using chirp-matching optical parametric chirped pulse amplification (OPCPA) scheme to eliminate the pre-pulse within the gain time window defined by the pump duration is proposed. The effects of the pump pulse shape, as well as the delay time between main pulse and pre-pulse on the improvement of signal-to-noise ratio are analyzed. using numerical simulation Comparing the chirp-matching OPCPA scheme with the conventional noncollinear OPCPA scheme, it is shown that the chirp-matching OPCPA scheme can eliminate a pre-pulse which is much closer to the main pulse, and it depends less on the pump pulse shape.
2012,
24: 399-402.
doi: 10.3788/HPLPB20122402.0399
Abstract:
In large aperture planar optics fabrication, the key process, large precision annular lapping, is difficult to control. The fabricating principle and essence of annular lapping were discussed in this paper. The disadvantages of conventional controlling method were figured out and a real-time off-line monitoring method was proposed. The new method features simple structure, fast measuring and judgment, and can response directly to the change of surface figures. Good results of real-time controlling and surface converging were obtained through experimental validation.
In large aperture planar optics fabrication, the key process, large precision annular lapping, is difficult to control. The fabricating principle and essence of annular lapping were discussed in this paper. The disadvantages of conventional controlling method were figured out and a real-time off-line monitoring method was proposed. The new method features simple structure, fast measuring and judgment, and can response directly to the change of surface figures. Good results of real-time controlling and surface converging were obtained through experimental validation.
2012,
24: 403-406.
doi: 10.3788/HPLPB20122402.0403
Abstract:
The dispersion characteristics and beam-wave interaction simulation results for a 140 GHz confocal gyro-travelling wave tube are presented with the help of CST Microwave Studio and 3D PIC software. The TE06 mode of a confocal waveguide is chosen as the operating mode. At a voltage of 35 kV, current of 2 A, and horizontal to vertical velocity ratio of 0.85, a 3 dB bandwidth of over 3.5 GHz is achieved in simulation, along with the peak output power of 2 kW and the peak saturated gain of over 30 dB, when the input power is about 1 W.
The dispersion characteristics and beam-wave interaction simulation results for a 140 GHz confocal gyro-travelling wave tube are presented with the help of CST Microwave Studio and 3D PIC software. The TE06 mode of a confocal waveguide is chosen as the operating mode. At a voltage of 35 kV, current of 2 A, and horizontal to vertical velocity ratio of 0.85, a 3 dB bandwidth of over 3.5 GHz is achieved in simulation, along with the peak output power of 2 kW and the peak saturated gain of over 30 dB, when the input power is about 1 W.
2012,
24: 407-411.
doi: 10.3788/HPLPB20122402.0407
Abstract:
A nonlinear description via the self-consistent coupling equations of waves with relativistic electron beam, is provided for the nonlinear interaction of multiple modes with the relativistic electron beam in cyclotron autoresonance maser(CARM), to analyze the mode competition in CARM. Specific analysis of a sub-terahertz (0.35 THz) CARM with higher-order mode TM51 and a large-orbit electron beam shows that, contrasted with, both larger output power and higher gain can be achieved for a CARM with TM operating mode. By optimizing parameters, the operating mode can play an absolutely dominant role while the competing modes are efficiently suppressed. However, a multi-mode nonlinear simulation must be performed for a higher-order terahertz CARM, because the output power is quite sensitive to the operating parameters.
A nonlinear description via the self-consistent coupling equations of waves with relativistic electron beam, is provided for the nonlinear interaction of multiple modes with the relativistic electron beam in cyclotron autoresonance maser(CARM), to analyze the mode competition in CARM. Specific analysis of a sub-terahertz (0.35 THz) CARM with higher-order mode TM51 and a large-orbit electron beam shows that, contrasted with, both larger output power and higher gain can be achieved for a CARM with TM operating mode. By optimizing parameters, the operating mode can play an absolutely dominant role while the competing modes are efficiently suppressed. However, a multi-mode nonlinear simulation must be performed for a higher-order terahertz CARM, because the output power is quite sensitive to the operating parameters.
2012,
24: 412-416.
doi: 10.3788/HPLPB20122402.0412
Abstract:
The paper adopts the Monte-Carlo method in the simulation and modeling of a rough sea surface, and uses the method of moment(MoM) to establish a model based on dual integral equations for transmission characteristics analysis of high-power microwave(HPM) at the sea surface. The model uses a smooth window function to modulate the incident uniform plane wave into a tapered one, which overcomes the edge effects caused by the sudden cutoff of the rough surface model. The model based on MoM is validated in comparison with Kirchhoff approximation, and it is used to analyze the impact of the rough sea surface geometry and sea water parameters on the HPM transmission coefficient. The results show that, the root-mean-square(RMS) height of rough sea surface affects the HPM transmission coefficient significantly, and larger RMS height leads to smaller transmission coefficient and more uniform energy distribution. The transmission coefficient increases as the real and imaginary parts of the sea water permittivity increase, and the impact of the real part is more evident.
The paper adopts the Monte-Carlo method in the simulation and modeling of a rough sea surface, and uses the method of moment(MoM) to establish a model based on dual integral equations for transmission characteristics analysis of high-power microwave(HPM) at the sea surface. The model uses a smooth window function to modulate the incident uniform plane wave into a tapered one, which overcomes the edge effects caused by the sudden cutoff of the rough surface model. The model based on MoM is validated in comparison with Kirchhoff approximation, and it is used to analyze the impact of the rough sea surface geometry and sea water parameters on the HPM transmission coefficient. The results show that, the root-mean-square(RMS) height of rough sea surface affects the HPM transmission coefficient significantly, and larger RMS height leads to smaller transmission coefficient and more uniform energy distribution. The transmission coefficient increases as the real and imaginary parts of the sea water permittivity increase, and the impact of the real part is more evident.
2012,
24: 417-422.
doi: 10.3788/HPLPB20122402.0417
Abstract:
A multi-aperture array coupling directional coupler was designed to measure the output power and monitor the spectrum for the 8 mm-band gyrotron. The formulas of multi-aperture coupling coefficient were derived based on loose-coupling theory. Coupling characteristics of equal-radius, binomial, Chebyshev and Gauss distributions were compared by numerical computation with Matlab and simulation with CST code, respectively. Then the composite distribution was proposed. The simulations demonstrate that the composite distribution obtains the advantages of multiple distributions simultaneously. It is beneficial for the improvement of directivity and has smaller ripples in inband coupling coefficient along with broader effective band. In addition, appropriate distribution of multi-aperture array such as Chebyshev distribution and proper distance between the two holes closest to the edge can improve the directivity effectively.
A multi-aperture array coupling directional coupler was designed to measure the output power and monitor the spectrum for the 8 mm-band gyrotron. The formulas of multi-aperture coupling coefficient were derived based on loose-coupling theory. Coupling characteristics of equal-radius, binomial, Chebyshev and Gauss distributions were compared by numerical computation with Matlab and simulation with CST code, respectively. Then the composite distribution was proposed. The simulations demonstrate that the composite distribution obtains the advantages of multiple distributions simultaneously. It is beneficial for the improvement of directivity and has smaller ripples in inband coupling coefficient along with broader effective band. In addition, appropriate distribution of multi-aperture array such as Chebyshev distribution and proper distance between the two holes closest to the edge can improve the directivity effectively.
2012,
24: 423-427.
doi: 10.3788/HPLPB20122402.0423
Abstract:
Based on the aperture field theory, near-field radiation behaviors of super-Gaussian circular aperture antenna are discussed, and the near-field gain expression at focusing point while focusing is obtained. Corresponding simulations are conducted by selecting different observing points of antenna. The results show that the radiation patterns keep invariant in spite of the ratio of aperture radius to beam waist(RAW), when the distance between the observing point and antenna is less than 0.3 times the focal length, and the super-Gaussian order is greater than 4. Once the observing point lies on the focus, for given RAW, the radiation patterns vary with the super-Gaussian order. However, when the RAW is over 4, the radiation patterns keep stable and no sidelobes exist for high-order beams.
Based on the aperture field theory, near-field radiation behaviors of super-Gaussian circular aperture antenna are discussed, and the near-field gain expression at focusing point while focusing is obtained. Corresponding simulations are conducted by selecting different observing points of antenna. The results show that the radiation patterns keep invariant in spite of the ratio of aperture radius to beam waist(RAW), when the distance between the observing point and antenna is less than 0.3 times the focal length, and the super-Gaussian order is greater than 4. Once the observing point lies on the focus, for given RAW, the radiation patterns vary with the super-Gaussian order. However, when the RAW is over 4, the radiation patterns keep stable and no sidelobes exist for high-order beams.
2012,
24: 428-430.
doi: 10.3788/HPLPB20122402.0428
Abstract:
The orthodox method for designing gradient refractive index lens requires that the feeding antenna possesses a steady phase center, which restricts the application of this lens. To break through the restriction, the paper presents a numerical method. By sampling the polarized electric field of the feeding antenna, phases of the electric field are got. Then they are used to design the gradient refractive index lens, which is fabricated from metamaterials with cut-wires structure. The design method is straightforward and flexible, with no restriction on the feeding antenna. Taking patch antenna as demonstration, the return losses and radiation patterns of the patch antenna and the lens antenna are compared. The data show that the lens obviously improves the gain and efficiency of the patch antenna. The gain is improved by 2 dB and the efficiency is increased from 62% to 99%.
The orthodox method for designing gradient refractive index lens requires that the feeding antenna possesses a steady phase center, which restricts the application of this lens. To break through the restriction, the paper presents a numerical method. By sampling the polarized electric field of the feeding antenna, phases of the electric field are got. Then they are used to design the gradient refractive index lens, which is fabricated from metamaterials with cut-wires structure. The design method is straightforward and flexible, with no restriction on the feeding antenna. Taking patch antenna as demonstration, the return losses and radiation patterns of the patch antenna and the lens antenna are compared. The data show that the lens obviously improves the gain and efficiency of the patch antenna. The gain is improved by 2 dB and the efficiency is increased from 62% to 99%.
2012,
24: 431-435.
doi: 10.3788/HPLPB20122402.0431
Abstract:
A gyrotron oscillator with effective interaction between high-order electromagnetic mode and high electron cyclotron mode is achieved through the analysis on mode selectivity of photonic-band-gap cavity(PBGC). By analyzing the characteristics of PBGC, TE23 is selected as the operating mode. The concept of equivalent radius for PBGC gyrotron is established and the self-consistent nonlinear theory and related numerical program are completed. The studies show that TE23 mode can interact with second-electronic cyclotron harmonics effectively with the coupling frequency of 206 GHz, and meanwhile reduces the required magnetic field significantly. With the oscillator parameters being optimized accordingly, a second-harmonic PBGC gyrotron oscillator with the wave-beam interaction efficiency of 21% is obtained, when the voltage, current and guiding magnetic field are 40 kV, 4.2 A and 3.925 T, respectively.
A gyrotron oscillator with effective interaction between high-order electromagnetic mode and high electron cyclotron mode is achieved through the analysis on mode selectivity of photonic-band-gap cavity(PBGC). By analyzing the characteristics of PBGC, TE23 is selected as the operating mode. The concept of equivalent radius for PBGC gyrotron is established and the self-consistent nonlinear theory and related numerical program are completed. The studies show that TE23 mode can interact with second-electronic cyclotron harmonics effectively with the coupling frequency of 206 GHz, and meanwhile reduces the required magnetic field significantly. With the oscillator parameters being optimized accordingly, a second-harmonic PBGC gyrotron oscillator with the wave-beam interaction efficiency of 21% is obtained, when the voltage, current and guiding magnetic field are 40 kV, 4.2 A and 3.925 T, respectively.
2012,
24: 436-440.
doi: 10.3788/HPLPB20122402.0436
Abstract:
The design of focusing lens based on traditional ray path method is introduced. The performances of 3 mm focusing lens antennas are simulated by using electromagnetic simulation software. Antennas with different spread angles (12,20,30) of horn are simulated. Its concluded that the actual focal length increases and approaches to the value designed gradually when the spread angle of horn increases, and the ray path method can be applied when the electromagnetic wavelength is short enough compared with the horn aperture. The E-field on the focal planes of the three antennas is presented and the focal spot of the antenna with 30 spread angle is smaller than twice the electromagnetic wavelength.
The design of focusing lens based on traditional ray path method is introduced. The performances of 3 mm focusing lens antennas are simulated by using electromagnetic simulation software. Antennas with different spread angles (12,20,30) of horn are simulated. Its concluded that the actual focal length increases and approaches to the value designed gradually when the spread angle of horn increases, and the ray path method can be applied when the electromagnetic wavelength is short enough compared with the horn aperture. The E-field on the focal planes of the three antennas is presented and the focal spot of the antenna with 30 spread angle is smaller than twice the electromagnetic wavelength.
2012,
24: 441-444.
doi: 10.3788/HPLPB20122402.0441
Abstract:
The microwave source for spatial power combining based on single beam klystron has been developed, which will meet the requirements of modern radars and high power equipments. The system composition, high power klystron, phase control and high power test system of the 50 MW super-high power klystron transmitter developed are introduced. The paper puts emphases on the key technologies of the transmitter， and provides some concrete solutions to the design difficulties. The design of the inductive-adder high-power all-solid-state modulator based on high-power IGBT modules as switches is presented, which can improve the reliability of the transmitter. The test results of the super-high power transmitter are given, which show that the transmitter satisfies technical requirements, and improvement methods for the transmitter are discussed. The future development of the microwave source for spatial power combining based on single beam klystron is forecasted.
The microwave source for spatial power combining based on single beam klystron has been developed, which will meet the requirements of modern radars and high power equipments. The system composition, high power klystron, phase control and high power test system of the 50 MW super-high power klystron transmitter developed are introduced. The paper puts emphases on the key technologies of the transmitter， and provides some concrete solutions to the design difficulties. The design of the inductive-adder high-power all-solid-state modulator based on high-power IGBT modules as switches is presented, which can improve the reliability of the transmitter. The test results of the super-high power transmitter are given, which show that the transmitter satisfies technical requirements, and improvement methods for the transmitter are discussed. The future development of the microwave source for spatial power combining based on single beam klystron is forecasted.
2012,
24: 445-448.
doi: 10.3788/HPLPB20122402.0445
Abstract:
For the determination of dielectric properties of low-loss materials in millimeter wave band, this paper describes a biconcave quasi-optical resonator with the Q factor over 0.8 million, which enables the determination of loss tangents down to the 10-5 range. The biconcave resonator system utilizes a phase-locked loop with harmonic mixer to synchronize a backward wave oscillator source and a microwave spectrum analyzer. The spectrum analyzer acquires high-resolution scan of the resonance curve. The Q factor of the cavity is calculated by performing a non-linear least squares fit to a Lorentzian line shape or by the resonance curve area method. The test results of quartz, CVD diamond and sapphire at ambient temperature are close to the data in the literatures, and the permittivity of 4H-SiC at 132.07 GHzare measuredto be 9.598 and the loss tangent to be 6.110-5。
For the determination of dielectric properties of low-loss materials in millimeter wave band, this paper describes a biconcave quasi-optical resonator with the Q factor over 0.8 million, which enables the determination of loss tangents down to the 10-5 range. The biconcave resonator system utilizes a phase-locked loop with harmonic mixer to synchronize a backward wave oscillator source and a microwave spectrum analyzer. The spectrum analyzer acquires high-resolution scan of the resonance curve. The Q factor of the cavity is calculated by performing a non-linear least squares fit to a Lorentzian line shape or by the resonance curve area method. The test results of quartz, CVD diamond and sapphire at ambient temperature are close to the data in the literatures, and the permittivity of 4H-SiC at 132.07 GHzare measuredto be 9.598 and the loss tangent to be 6.110-5。
2012,
24: 449-452.
doi: 10.3788/HPLPB20122402.0449
Abstract:
According to the SLED(SLAC energy doubler) working principle, the error effect of the 3 dB coupler on the SLED performance has been studied theoretically. In the meantime, the effect of the 3 dB coupler on the SLED used in the BEPC and BEPC Ⅱ linac is investigated. These analyses provide theoretical reference for judging the waveguide distortion of the 3 dB directional coupler after final assembly and welding. Both power imbalance error and phase difference deviation will cause reflection of the RF power back to the klystron. The larger the power imbalance error and the phase difference deviation are, the more the power multiplication factor decreases.
According to the SLED(SLAC energy doubler) working principle, the error effect of the 3 dB coupler on the SLED performance has been studied theoretically. In the meantime, the effect of the 3 dB coupler on the SLED used in the BEPC and BEPC Ⅱ linac is investigated. These analyses provide theoretical reference for judging the waveguide distortion of the 3 dB directional coupler after final assembly and welding. Both power imbalance error and phase difference deviation will cause reflection of the RF power back to the klystron. The larger the power imbalance error and the phase difference deviation are, the more the power multiplication factor decreases.
2012,
24: 453-456.
doi: 10.3788/HPLPB20122402.0453
Abstract:
This paper reports the 2D/3D field calculations and designs of DC current septum magnet of injection system for rapid cycling synchrotron of the China Spallation Neutron Source (CSNS/RCS). The stray field ratio shrinks to 0.26 with 1 mmthick DT4 iron board, which greatly reduces the impacts on the cycling beam dynamics. Additionally, the detailed calculation of coil water cooling system has also been performed very carefully, which ensures stable running of the septum magnet. The results show that this type of septum magnet will the requirements of the long term stable running of CSNS/RCS on both physics and engineering design.
This paper reports the 2D/3D field calculations and designs of DC current septum magnet of injection system for rapid cycling synchrotron of the China Spallation Neutron Source (CSNS/RCS). The stray field ratio shrinks to 0.26 with 1 mmthick DT4 iron board, which greatly reduces the impacts on the cycling beam dynamics. Additionally, the detailed calculation of coil water cooling system has also been performed very carefully, which ensures stable running of the septum magnet. The results show that this type of septum magnet will the requirements of the long term stable running of CSNS/RCS on both physics and engineering design.
2012,
24: 457-462.
doi: 10.3788/HPLPB20122402.0457
Abstract:
In order to measure the beam emittance which is space charge dominated, a slit-based emittance measurement system is applied in Hefei Light Source(HLS). Two types of slit masks are chosen: multi-slit one and single-slit one. Measurement results show that, single-slit based emittance measurement yields closer results to the simulation value. Moreover, single-slit based emittance measurement can avoid the overlapping between adjacent beamlets, which makes its application range wider than multi-slit technique. The experiment result shows that with the beam charge of 240 pC, normalized emittance of (1.840.085) mmmrad can be achieved at HLS.
In order to measure the beam emittance which is space charge dominated, a slit-based emittance measurement system is applied in Hefei Light Source(HLS). Two types of slit masks are chosen: multi-slit one and single-slit one. Measurement results show that, single-slit based emittance measurement yields closer results to the simulation value. Moreover, single-slit based emittance measurement can avoid the overlapping between adjacent beamlets, which makes its application range wider than multi-slit technique. The experiment result shows that with the beam charge of 240 pC, normalized emittance of (1.840.085) mmmrad can be achieved at HLS.
2012,
24: 463-466.
doi: 10.3788/HPLPB20122402.0463
Abstract:
Hardening trends of X-ray beams from three X-ray machines of different energies traversing aluminium plates of different thickness were simulated by means of Monte-Carlo method, as well as the processes of areal density measuring，and corresponding experimental researchwas done.The effects of X-ray beams hardening on the measurement sensitivity were analyzed. For the X-ray beams from X-ray machine the same energy, X-ray beams harden more with the areal density increasing, which brings about the reduction of the measurement sensitivity;The lower the energy of photons is , the more quicklythe measurement sensitivity reduces, and vice versa. For a certain areal density range, when X-ray photons can just traverse the part of the maximum areal density by adjusting the X-ray tube voltage, the best measurement sensitivity can be obtained.
Hardening trends of X-ray beams from three X-ray machines of different energies traversing aluminium plates of different thickness were simulated by means of Monte-Carlo method, as well as the processes of areal density measuring，and corresponding experimental researchwas done.The effects of X-ray beams hardening on the measurement sensitivity were analyzed. For the X-ray beams from X-ray machine the same energy, X-ray beams harden more with the areal density increasing, which brings about the reduction of the measurement sensitivity;The lower the energy of photons is , the more quicklythe measurement sensitivity reduces, and vice versa. For a certain areal density range, when X-ray photons can just traverse the part of the maximum areal density by adjusting the X-ray tube voltage, the best measurement sensitivity can be obtained.
2012,
24: 467-470.
doi: 10.3788/HPLPB20122402.0467
Abstract:
The proton beam accelerated by target normal sheath acceleration (TNSA) mechanism has a wide energy spectrum, which limits its applications. In order to produce quasi-monoenergetic proton beams, the energy spectrum optimization method based on RF cavity has been investigated. At given RF voltage and frequency, the relationship of the cavity length and the optimization energy was calculated and spectrum optimization with different cavity lengths and cavity numbers was designed for different energy. For given number of cavities, only a certain energy range can get the minimum energy divergence. The energy acceptance has been analyzed. To get the final energy divergence of 2%, the energy divergence of the proton beam before entering RF cavity should not be over 15%. The energy acceptance affected by the RF frequency has also been analyzed. Finally a spectrum calculated by the particle-in-cell simulation with the divergence about 15% was optimized through the RF cavity, and a quasi-monoenergetic proton beam with the energy divergence lower than 2% was obtained.
The proton beam accelerated by target normal sheath acceleration (TNSA) mechanism has a wide energy spectrum, which limits its applications. In order to produce quasi-monoenergetic proton beams, the energy spectrum optimization method based on RF cavity has been investigated. At given RF voltage and frequency, the relationship of the cavity length and the optimization energy was calculated and spectrum optimization with different cavity lengths and cavity numbers was designed for different energy. For given number of cavities, only a certain energy range can get the minimum energy divergence. The energy acceptance has been analyzed. To get the final energy divergence of 2%, the energy divergence of the proton beam before entering RF cavity should not be over 15%. The energy acceptance affected by the RF frequency has also been analyzed. Finally a spectrum calculated by the particle-in-cell simulation with the divergence about 15% was optimized through the RF cavity, and a quasi-monoenergetic proton beam with the energy divergence lower than 2% was obtained.
2012,
24: 471-475.
doi: 10.3788/HPLPB20122402.0475
Abstract:
In a radiographic imaging system, the created light along the thickness direction of the scintillator is focused by a lens to form a blurred image, which is a limiting factor for the spatial resolution of the imaging system. Geometric optics models have been developed to describe the imaging process. To parameterize the spatial resolution, the standard deviation of the blurred image has been expressed by the parameters of the imaging system. A method is found to optimize the position of a thick scintillator with respect to the object focal plane of the lens, in which the deviation of the blurred image will be minimized.
In a radiographic imaging system, the created light along the thickness direction of the scintillator is focused by a lens to form a blurred image, which is a limiting factor for the spatial resolution of the imaging system. Geometric optics models have been developed to describe the imaging process. To parameterize the spatial resolution, the standard deviation of the blurred image has been expressed by the parameters of the imaging system. A method is found to optimize the position of a thick scintillator with respect to the object focal plane of the lens, in which the deviation of the blurred image will be minimized.
2012,
24: 476-480.
doi: 10.3788/HPLPB20122402.0476
Abstract:
To improve the quality of laser-induced breakdown spectroscopy, the nanosecond pulse laser generated by Nd:YAG laser was used to excite soil samples. The plasma spectrum was observed using a grating spectrometer and a photoelectric detection system. The influence of laser output energy ranging from 100 mJ to 500 mJ and NaCl additive content ranging from 0% to 20% on the radiation intensity of plasma was studied. The experimental results show that both the line intensity and the signal-to-background ratio can be enhanced under the optimized condition that the laser energy is 200 mJ, and further increase of laser energy generates serious self-absorption effect in the laser-induced plasma. However, further improvement of spectrum quality was observed with adding proper amount of NaCl additive into the soil sample. For instance, when the content of NaCl additive is 10%, the spectral line intensities of elements Fe, Ba, Al and Ti increase around 37%, 32%, 32% and 70% than those without additive; the spectral signal-to-background ratios increase about 33%, 26%, 16% and 38%; while the ablation mass, electron temperature and electron density of plasmas go up 14%, 9.6% and 26%, respectively.
To improve the quality of laser-induced breakdown spectroscopy, the nanosecond pulse laser generated by Nd:YAG laser was used to excite soil samples. The plasma spectrum was observed using a grating spectrometer and a photoelectric detection system. The influence of laser output energy ranging from 100 mJ to 500 mJ and NaCl additive content ranging from 0% to 20% on the radiation intensity of plasma was studied. The experimental results show that both the line intensity and the signal-to-background ratio can be enhanced under the optimized condition that the laser energy is 200 mJ, and further increase of laser energy generates serious self-absorption effect in the laser-induced plasma. However, further improvement of spectrum quality was observed with adding proper amount of NaCl additive into the soil sample. For instance, when the content of NaCl additive is 10%, the spectral line intensities of elements Fe, Ba, Al and Ti increase around 37%, 32%, 32% and 70% than those without additive; the spectral signal-to-background ratios increase about 33%, 26%, 16% and 38%; while the ablation mass, electron temperature and electron density of plasmas go up 14%, 9.6% and 26%, respectively.
2012,
24: 481-485.
doi: 10.3788/HPLPB20122402.0481
Abstract:
On the basis of the dominant physical processes of secondary electron emission, the relationship among secondary electron yield, the ratio of the mean secondary electron generation of one backscattered electron to that one of a primary electron, primary energy, the parameter E(z), maximum yield and backscattered electron coefficient was deduced. From the experimental results, the formula for the ratio in the energy range of 2 to 10 keV was given. Based on the relationship deduced, the parameters E(z) related to six metals were computed with experimental results, respectively. The parameter E(z) related to six metals is found to be approximately 11.89(eV)0.5. Based on the deduced relationship and the computed parameter, a universal formula for expressing the secondary electron yield as a function of maximum yield, backscattered electron coefficient and the primary energy was deduced. The secondary electron yield calculated from this universal formula and the yields measured experimentally from metals were compared. Therefore, the formula presented is universal for secondary electron yields from metals in the energy range of 2 to 10 keV.
On the basis of the dominant physical processes of secondary electron emission, the relationship among secondary electron yield, the ratio of the mean secondary electron generation of one backscattered electron to that one of a primary electron, primary energy, the parameter E(z), maximum yield and backscattered electron coefficient was deduced. From the experimental results, the formula for the ratio in the energy range of 2 to 10 keV was given. Based on the relationship deduced, the parameters E(z) related to six metals were computed with experimental results, respectively. The parameter E(z) related to six metals is found to be approximately 11.89(eV)0.5. Based on the deduced relationship and the computed parameter, a universal formula for expressing the secondary electron yield as a function of maximum yield, backscattered electron coefficient and the primary energy was deduced. The secondary electron yield calculated from this universal formula and the yields measured experimentally from metals were compared. Therefore, the formula presented is universal for secondary electron yields from metals in the energy range of 2 to 10 keV.
2012,
24: 486-490.
doi: 10.3788/HPLPB20122402.0486
Abstract:
High intensity pulsed ion beam (C+, H+) irradiation of casting magnesium alloy AZ31 target is carried out with shot times of 1, 5, 10, 20, 30, 50 and 100, respectively. The surface morphologies, phase structure, surface and cross-sectional microhardness ofirradiated samples are characterized. The results show that the shot times of HIPIB irradiation play a great role on the target morphology, subsequent irradiation on the melting crater has previously generated fuzzy or eliminated the trend; melting craters appear again along with increasing the times of irradiation. The surface microhardness increases straightly after the first to 30th irradiation, lying in grain refinement and micro-strain caused by the crystal defects;the 30th to 50th exposure,there is a significant reduction in microhardness,which lies in the evolution of crystal defects, such as dislocation movement leading to the formation of small angle grain boundaries, or even reply recrystallization;the 50th to 100th irradiation slightly reduced the surface hardness, the reason is that radiation's organizational structure and thermodynamic behavior of the surface to reach a steady state. The shock-wave effects the formation of long-hardening.The cross-sectional microhardness away from the surface 30 and 240 m of AZ31,which is 20th irradiation,reach a great value 1.0 GPa and 1.3 GPa,respectively.
High intensity pulsed ion beam (C+, H+) irradiation of casting magnesium alloy AZ31 target is carried out with shot times of 1, 5, 10, 20, 30, 50 and 100, respectively. The surface morphologies, phase structure, surface and cross-sectional microhardness ofirradiated samples are characterized. The results show that the shot times of HIPIB irradiation play a great role on the target morphology, subsequent irradiation on the melting crater has previously generated fuzzy or eliminated the trend; melting craters appear again along with increasing the times of irradiation. The surface microhardness increases straightly after the first to 30th irradiation, lying in grain refinement and micro-strain caused by the crystal defects;the 30th to 50th exposure,there is a significant reduction in microhardness,which lies in the evolution of crystal defects, such as dislocation movement leading to the formation of small angle grain boundaries, or even reply recrystallization;the 50th to 100th irradiation slightly reduced the surface hardness, the reason is that radiation's organizational structure and thermodynamic behavior of the surface to reach a steady state. The shock-wave effects the formation of long-hardening.The cross-sectional microhardness away from the surface 30 and 240 m of AZ31,which is 20th irradiation,reach a great value 1.0 GPa and 1.3 GPa,respectively.
2012,
24: 491-496.
doi: 10.3788/HPLPB20122402.0491
Abstract:
This paper investigates the generation and spatial propagating properties of vacuum discharge plasma with cone-plate and cone-mesh electrode configurations. Under the condition of single pulse discharge where the discharge current is 200 A and the discharge duration is 13 s, the property parameters of the generated plasma, such as electron density, electron temperature, space potential, and ions energy, are measured by the probe method. The experiment and simulation results show that the initial voltage of the cone-mesh electrode configuration is higher and the density of the generated plasma is larger. Moreover, the plasma moving along the axial direction of the electrodes possesses the largest density. However, the propagation velocities of the plasmas generated by the two kinds of electrode configurations show no apparent difference.
This paper investigates the generation and spatial propagating properties of vacuum discharge plasma with cone-plate and cone-mesh electrode configurations. Under the condition of single pulse discharge where the discharge current is 200 A and the discharge duration is 13 s, the property parameters of the generated plasma, such as electron density, electron temperature, space potential, and ions energy, are measured by the probe method. The experiment and simulation results show that the initial voltage of the cone-mesh electrode configuration is higher and the density of the generated plasma is larger. Moreover, the plasma moving along the axial direction of the electrodes possesses the largest density. However, the propagation velocities of the plasmas generated by the two kinds of electrode configurations show no apparent difference.
2012,
24: 497-500.
doi: 10.3788/HPLPB20122402.0497
Abstract:
According to the particular structures and working principles of high voltage semiconductor switches, drift step recovery diodes and fast ionization devices, a high pulse repetition frequency(PRF) and high voltage nanosecond electromagnetic pulse generation method is provided. The technology path is to transmit the high energy of storage inductance on the FID and load through the DSRD.The feasibility of the method is tested and verified by experiments under input trigger PRFs as high as 120, 200 and 300 kHz, and the output pulse voltages are 1.62, 1.41 and 1.36 kV, respectively.
According to the particular structures and working principles of high voltage semiconductor switches, drift step recovery diodes and fast ionization devices, a high pulse repetition frequency(PRF) and high voltage nanosecond electromagnetic pulse generation method is provided. The technology path is to transmit the high energy of storage inductance on the FID and load through the DSRD.The feasibility of the method is tested and verified by experiments under input trigger PRFs as high as 120, 200 and 300 kHz, and the output pulse voltages are 1.62, 1.41 and 1.36 kV, respectively.
2012,
24: 501-504.
doi: 10.3788/HPLPB20122402.0501
Abstract:
This paper puts forward a field calibration method of differential ring for nanosecond pulse current measurement after analyzing the problems in calibration. To resolve the low signal-to-noise ratio and low reliability issues, the pulse charging principle of pulse forming line is analyzed. The relation between calibration result and charging capacitance, charging inductance, pulse forming line voltage and pulse forming switch breakdown voltage is also analyzed. Field calibration of the differential ring for pulsed electron beam current measurement is conducted on the Flash Ⅱ accelerator. When the average breakdown voltage of the front gap switch is 25 kV, the calibration current is 1.3 kA, the average sensitivity of the differential ring is 9.311010 with a deviation of 0.151010.
This paper puts forward a field calibration method of differential ring for nanosecond pulse current measurement after analyzing the problems in calibration. To resolve the low signal-to-noise ratio and low reliability issues, the pulse charging principle of pulse forming line is analyzed. The relation between calibration result and charging capacitance, charging inductance, pulse forming line voltage and pulse forming switch breakdown voltage is also analyzed. Field calibration of the differential ring for pulsed electron beam current measurement is conducted on the Flash Ⅱ accelerator. When the average breakdown voltage of the front gap switch is 25 kV, the calibration current is 1.3 kA, the average sensitivity of the differential ring is 9.311010 with a deviation of 0.151010.
