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RSS1992 Vol. 04, No. 02
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1992,
04: 165-174.
Abstract:
By use of "series multi-target coupling", the Ne-like Ge soft x-ray lasers output at wavelengths of 23.2 and 23.6nm were observed on a line-focused two-beam Nd-glass laser at 1.05μm. The pulse width was about 1ns, while the irradiance 0.8 × 1013～1.0× 1013W/cm2 on the target surface. For the total target length of 5.6cm, GL values reached 16 or so, and the divergence angles in the directions of both the target normal and target plane were all 3～4mrad.
By use of "series multi-target coupling", the Ne-like Ge soft x-ray lasers output at wavelengths of 23.2 and 23.6nm were observed on a line-focused two-beam Nd-glass laser at 1.05μm. The pulse width was about 1ns, while the irradiance 0.8 × 1013～1.0× 1013W/cm2 on the target surface. For the total target length of 5.6cm, GL values reached 16 or so, and the divergence angles in the directions of both the target normal and target plane were all 3～4mrad.
1992,
04: 175-180.
Abstract:
An x-ray streaked crystal spectrometer developed by ourselves was first used to measure time-resolved x-ray spectra from line-plasmas of Ge. The time evolutions of the resonance lines of the Ge L-shell spectra were obtained. Also, the electron temperature and its time evolution have been deduced by means of the line-intensity-ratio of the dielectronic capture satellite lines to the resonance lines of the Ge L-shell spectra. The electron temperature in the gain region is approximately 400-760eV, and the period having the relative constant electron temperature is at least 90ps (the variation of the electron temperature is less than 2%).
An x-ray streaked crystal spectrometer developed by ourselves was first used to measure time-resolved x-ray spectra from line-plasmas of Ge. The time evolutions of the resonance lines of the Ge L-shell spectra were obtained. Also, the electron temperature and its time evolution have been deduced by means of the line-intensity-ratio of the dielectronic capture satellite lines to the resonance lines of the Ge L-shell spectra. The electron temperature in the gain region is approximately 400-760eV, and the period having the relative constant electron temperature is at least 90ps (the variation of the electron temperature is less than 2%).
1992,
04: 181-185.
Abstract:
Because of electron density gradients, refraction will occur when x rays propagate in plasmas. Refraction tends to go direct the x rays out of high density regions, shortening the distance that x rays can travel within the plasmas, and limiting the amplification thereby. In thick target, refraction is more serious. Double- targets coupling design can lessen refraction .In this paper, we suppose that the density and gain profiles within the plasma are linear and find that refraction introduces a loss term to the laser amplification.Theoretical simulations for x-rays refraction in the gain region are shown.
Because of electron density gradients, refraction will occur when x rays propagate in plasmas. Refraction tends to go direct the x rays out of high density regions, shortening the distance that x rays can travel within the plasmas, and limiting the amplification thereby. In thick target, refraction is more serious. Double- targets coupling design can lessen refraction .In this paper, we suppose that the density and gain profiles within the plasma are linear and find that refraction introduces a loss term to the laser amplification.Theoretical simulations for x-rays refraction in the gain region are shown.
1992,
04: 186-200.
Abstract:
A study of electron impact excitation of charged ions is reported here.Electron collision strengths and oscillator strengths have been calculated using plane—wave and Coulomb—wave Born approximation with configuration interactions. The corresponding programs MCPBA(9) and MCCBX(9) have been compiled. As an example, we give the calculation results of Nc-like Ge ion with 27 levels and 4 configurations from its ground state. 13 different processes which contain direct collision only have been calculated with MCPBA (9). The collision strengths of 26 different processes which include exchange collisions have also been calculated with MCPBA (9). The effect of wavefunction on the collision strengths has been examined. Our results are compared with the available results of distorted wave. It has been found from the result that the accuracy of the target wave function is much more important than that of the collision electron wave function.
A study of electron impact excitation of charged ions is reported here.Electron collision strengths and oscillator strengths have been calculated using plane—wave and Coulomb—wave Born approximation with configuration interactions. The corresponding programs MCPBA(9) and MCCBX(9) have been compiled. As an example, we give the calculation results of Nc-like Ge ion with 27 levels and 4 configurations from its ground state. 13 different processes which contain direct collision only have been calculated with MCPBA (9). The collision strengths of 26 different processes which include exchange collisions have also been calculated with MCPBA (9). The effect of wavefunction on the collision strengths has been examined. Our results are compared with the available results of distorted wave. It has been found from the result that the accuracy of the target wave function is much more important than that of the collision electron wave function.
1992,
04: 201-208.
Abstract:
By means of microwave discharge the reaction mechanism of NH3-F-F2-CF3I system is experimentally investigated, and the conclusion has been reached that the production of IF(B)is mainly due to the energy transfer between N2(A), N(2D) and IF(X). This is confirmed by another experiment, in which CF3I reacts directly with microwave excited N2 gas.
By means of microwave discharge the reaction mechanism of NH3-F-F2-CF3I system is experimentally investigated, and the conclusion has been reached that the production of IF(B)is mainly due to the energy transfer between N2(A), N(2D) and IF(X). This is confirmed by another experiment, in which CF3I reacts directly with microwave excited N2 gas.
1992,
04: 209-214.
Abstract:
Stimulated Raman amplification in a collinear geometry is studied where high-pressure H2 is pumped by a KrF laser and simultaneously the first Stokes beam (s1)is injected .The conversion efficiency of s1 is about 17.2%. The factors that affect the amplification and the conversion efficiency are analysed.
Stimulated Raman amplification in a collinear geometry is studied where high-pressure H2 is pumped by a KrF laser and simultaneously the first Stokes beam (s1)is injected .The conversion efficiency of s1 is about 17.2%. The factors that affect the amplification and the conversion efficiency are analysed.
1992,
04: 215-222.
Abstract:
Single slit and probe method has been used for measuring the beam emittance of an electron gun. Amovable slit 0.1mm wide is used for sampling .A probe 0.1mmin diameter parallel to the slit and moving at a constant velocity, is used to catch the beam through the slit. Using geometrical relation, the divergence r1' and r2' of the beam through the slit can be calculated.
In our device, the distance between the slit and the probe is 59mm, the angle resolution is 3.4mrad, and the maximum system acceptance is 6.4× 10-1cm·rad. A mechanism is designed to adjust the depth of parallelism between the slit and probe in order to improve the measurement accuracy. There is water cooled structure in the slit plate, which can bear higher beam power. With fine shielding and rational second- electron suppressor, the current of the order of 10-10 A has been clearly measured. The relative error of the measured phase plots is about 8%.
The system is useful to study the effects on the emittance, of electron energy, the grid pulse voltage, cathode temperature, pulse current intensity.
Single slit and probe method has been used for measuring the beam emittance of an electron gun. Amovable slit 0.1mm wide is used for sampling .A probe 0.1mmin diameter parallel to the slit and moving at a constant velocity, is used to catch the beam through the slit. Using geometrical relation, the divergence r1' and r2' of the beam through the slit can be calculated.
In our device, the distance between the slit and the probe is 59mm, the angle resolution is 3.4mrad, and the maximum system acceptance is 6.4× 10-1cm·rad. A mechanism is designed to adjust the depth of parallelism between the slit and probe in order to improve the measurement accuracy. There is water cooled structure in the slit plate, which can bear higher beam power. With fine shielding and rational second- electron suppressor, the current of the order of 10-10 A has been clearly measured. The relative error of the measured phase plots is about 8%.
The system is useful to study the effects on the emittance, of electron energy, the grid pulse voltage, cathode temperature, pulse current intensity.
1992,
04: 223-227.
Abstract:
Starting with a problem encountered in the design of pulsed beam system, We derive strictly equations of particle motions in 6D phase space from vector motion equations.
Starting with a problem encountered in the design of pulsed beam system, We derive strictly equations of particle motions in 6D phase space from vector motion equations.
1992,
04: 228-232.
Abstract:
The discharge circuit of a Marx generator is analysed in this paper and a common calculating program is given. On the basis of theoretical analysis, a high voltage fast-rise pulse generator, whose output voltage is 160kV, and rise-time is less than 5ns, has been designed and manufactured.
The discharge circuit of a Marx generator is analysed in this paper and a common calculating program is given. On the basis of theoretical analysis, a high voltage fast-rise pulse generator, whose output voltage is 160kV, and rise-time is less than 5ns, has been designed and manufactured.
1992,
04: 233-238.
Abstract:
Rogowski coil is an available device for measuring steep impulse current with a response rise time of ns level. However, it can only work linearly in certain frequency range. This paper describes the measured results of the Rogowski coil made by Xi'an Jiaotong University, to gain a better understanding its frequency characteristics.
This paper emphatically introduces the method for measuring frequency response-the method of point frequency and discusses the relevant influence factors, such as the signal generator, standard voltmeter and matching load etc. The measured curve of frequency response and the measured results for various lumped parameters of the Rogowski coil itself have been described.
Rogowski coil is an available device for measuring steep impulse current with a response rise time of ns level. However, it can only work linearly in certain frequency range. This paper describes the measured results of the Rogowski coil made by Xi'an Jiaotong University, to gain a better understanding its frequency characteristics.
This paper emphatically introduces the method for measuring frequency response-the method of point frequency and discusses the relevant influence factors, such as the signal generator, standard voltmeter and matching load etc. The measured curve of frequency response and the measured results for various lumped parameters of the Rogowski coil itself have been described.
1992,
04: 239-244.
Abstract:
Reflectivities and spatial distributions of reflected light was measured with a multi ?chanell apparatus for 1.06μm laser pulses interacting with LY12 aluminum targets in 1 atm air. As the laser power density changed from 1.68×l04 to 6.08 × 104W/cm2 with target surface roughness 1.6～3.2μm, the reflectivity reduced from 0.90 to 0.8 for long pulses. For 2.83 × 108 W/cm2 short pulses, its reflectivity was 0.78. The experiments indicated that reflectivity and thd spatial dlistribution of the reflected light was dependent on the temperature field of the targets, optical property of ablated surface and the mechanism of laser energy absorption by vapor plume.
Reflectivities and spatial distributions of reflected light was measured with a multi ?chanell apparatus for 1.06μm laser pulses interacting with LY12 aluminum targets in 1 atm air. As the laser power density changed from 1.68×l04 to 6.08 × 104W/cm2 with target surface roughness 1.6～3.2μm, the reflectivity reduced from 0.90 to 0.8 for long pulses. For 2.83 × 108 W/cm2 short pulses, its reflectivity was 0.78. The experiments indicated that reflectivity and thd spatial dlistribution of the reflected light was dependent on the temperature field of the targets, optical property of ablated surface and the mechanism of laser energy absorption by vapor plume.
1992,
04: 245-250.
Abstract:
Effects of ion energy, ion current intensity and ion species on refractive indices, optical absorptance and laser- induced damage thresholds of TiO2, ZrO2, SiO2 coatings deposited using ion assisted deposition were investigated.
Effects of ion energy, ion current intensity and ion species on refractive indices, optical absorptance and laser- induced damage thresholds of TiO2, ZrO2, SiO2 coatings deposited using ion assisted deposition were investigated.
1992,
04: 251-254.
Abstract:
This paper represents the measuring principle of the solid rapid thermal strain induced by high intensity laser light using temperature compensation resistance strain gauges, and introduces measurements of aluminium alloy exposed to a high intensity CW-CO2 laser beam. The results show that this measurement method is available for the solid rapid thermal strain induced by a second duration laser beam.
This paper represents the measuring principle of the solid rapid thermal strain induced by high intensity laser light using temperature compensation resistance strain gauges, and introduces measurements of aluminium alloy exposed to a high intensity CW-CO2 laser beam. The results show that this measurement method is available for the solid rapid thermal strain induced by a second duration laser beam.
1992,
04: 255-259.
Abstract:
The ripple phenomena on thin film mirror surface induced by laser irradiation and it's mechanism are discussed in ths article, and it's found that heat-conduction wave model propose by us can give a better explanation about it than common optical model.
The ripple phenomena on thin film mirror surface induced by laser irradiation and it's mechanism are discussed in ths article, and it's found that heat-conduction wave model propose by us can give a better explanation about it than common optical model.
1992,
04: 260-268.
Abstract:
Relativistic electron beam-plasma devices have the potential as one of the newest high-power microwave sources. In this paper, the process of microwave radiation at ωp from beam-plasma interaction is investigated for nb/np≈ 0.01, where nb is the beam electron density and np the plasma density. The main instabilities have been analysed using the linear and nonlinear (Zakharov) dispersion relations. The dispersion relation of parametric decay by which unstable electrostatic waves are converted into electromagnetic waves has been derived. From this, the radiation rate of a beam-plasma system has also been obtained. Finally, we model how the energy flows from beam kinetic energy to plasma waves, then to EM radiation and plasma heating.
Relativistic electron beam-plasma devices have the potential as one of the newest high-power microwave sources. In this paper, the process of microwave radiation at ωp from beam-plasma interaction is investigated for nb/np≈ 0.01, where nb is the beam electron density and np the plasma density. The main instabilities have been analysed using the linear and nonlinear (Zakharov) dispersion relations. The dispersion relation of parametric decay by which unstable electrostatic waves are converted into electromagnetic waves has been derived. From this, the radiation rate of a beam-plasma system has also been obtained. Finally, we model how the energy flows from beam kinetic energy to plasma waves, then to EM radiation and plasma heating.
1992,
04: 269-276.
Abstract:
In this paper, the operation of a relativistic BWO is briefly described. The experimental equipments and the measurement method are described in detail. The results of the first experiment are given. The peak power of the relativistic BWO is about 981MW in 3cm-band and the efficiency is about 10%.
In this paper, the operation of a relativistic BWO is briefly described. The experimental equipments and the measurement method are described in detail. The results of the first experiment are given. The peak power of the relativistic BWO is about 981MW in 3cm-band and the efficiency is about 10%.
1992,
04: 277-283.
Abstract:
A theoretic model is made to interpret how the phase of the pump laser beam couples with the intensities of Stokes waves produced by the pump laser beam transimitting in a long path air, This model has clariffied the physical mechanism of how the stimulated Raman scattering (S RS) influences the quality of the transimitted pump laser beam. the results of the theoretic research have shown it is the SRS and the nonhomogeneity of the pump laser beam that make the wave plane of the transimitted pump laser beam distorted, resulting in its quality degradation. This conclusion agrees qualitatively with the experimental results in which the far-field divergency angle of the transimitted pump laser beam θp increases with the increment of the Stokes energy conversion ratio ηs. In addition, the experimental results also show that the pulse duration of the transimitted pump laser beam is almost unaffected by SRS when the ηs <5%. but becomes compressed and " Red shift" takes place in the pulse tail of the transimitted pump beam when ηs>5%.
A theoretic model is made to interpret how the phase of the pump laser beam couples with the intensities of Stokes waves produced by the pump laser beam transimitting in a long path air, This model has clariffied the physical mechanism of how the stimulated Raman scattering (S RS) influences the quality of the transimitted pump laser beam. the results of the theoretic research have shown it is the SRS and the nonhomogeneity of the pump laser beam that make the wave plane of the transimitted pump laser beam distorted, resulting in its quality degradation. This conclusion agrees qualitatively with the experimental results in which the far-field divergency angle of the transimitted pump laser beam θp increases with the increment of the Stokes energy conversion ratio ηs. In addition, the experimental results also show that the pulse duration of the transimitted pump laser beam is almost unaffected by SRS when the ηs <5%. but becomes compressed and " Red shift" takes place in the pulse tail of the transimitted pump beam when ηs>5%.
1992,
04: 284-290.
Abstract:
We present an algorithm for producing conjugation field using two deformable mirrors. The algorithm is demonstrated effective by simulations using a Gaussian beam as the source. The simulations shows that the smooth surface of deformable mirrors eliminates the the local phase fluctuations on the first mirror, evidently improving the intensity pattern on the second mirror, and that for a Gaussian beam, the needed phase plane is very easy to be constructed by deformable mirrors. The effects of the distance between the mirrors is also discussed. Finally, we point out how to improve the present algorithm.
We present an algorithm for producing conjugation field using two deformable mirrors. The algorithm is demonstrated effective by simulations using a Gaussian beam as the source. The simulations shows that the smooth surface of deformable mirrors eliminates the the local phase fluctuations on the first mirror, evidently improving the intensity pattern on the second mirror, and that for a Gaussian beam, the needed phase plane is very easy to be constructed by deformable mirrors. The effects of the distance between the mirrors is also discussed. Finally, we point out how to improve the present algorithm.
1992,
04: 291-298.
Abstract:
This paper introduces a method to measure neutron yields, produced in laser-driven DT-filled targets using recently developed arrays of BF3 counters and especially describes the design and characterisitics of the arrays, manufacture and effect of the time gate at the high voltage circuit, and results of the measurement at the "Shenguang" facility in 1990.
This paper introduces a method to measure neutron yields, produced in laser-driven DT-filled targets using recently developed arrays of BF3 counters and especially describes the design and characterisitics of the arrays, manufacture and effect of the time gate at the high voltage circuit, and results of the measurement at the "Shenguang" facility in 1990.
1992,
04: 299-304.
Abstract:
Based on Prof. Yumin's FEL longitudinal mode theory[1], the small signal and exponential growth rates including the effect of wiggler magnetic field random errors have been obtained, and with SG-1 parameters, the scaling relation between exponential growth rate parameter g0 and magnetic field random error σ is provided. The results of linear theory have been verified by 3-D simulations.
Based on Prof. Yumin's FEL longitudinal mode theory[1], the small signal and exponential growth rates including the effect of wiggler magnetic field random errors have been obtained, and with SG-1 parameters, the scaling relation between exponential growth rate parameter g0 and magnetic field random error σ is provided. The results of linear theory have been verified by 3-D simulations.
1992,
04: 305-313.
Abstract:
A set of eigenmodes of radiation field is obtained in the media with quadratic equivalent index of refraction. Taking the set of eigenmodes as expansion basis, the fully 3-D problems relative to free electron lasers can be solved in the frame of perturbation approach. The optical guiding of FELs by the off-axis displacement of the eletron beam is treated as an example of 3D-FEL problems.
A set of eigenmodes of radiation field is obtained in the media with quadratic equivalent index of refraction. Taking the set of eigenmodes as expansion basis, the fully 3-D problems relative to free electron lasers can be solved in the frame of perturbation approach. The optical guiding of FELs by the off-axis displacement of the eletron beam is treated as an example of 3D-FEL problems.
1992,
04: 314-318.
Abstract:
The design of a high performance short-period wiggler is introduced, Tunableness to magnetic field in half period length has been achieved by slot location of separate permanent magnet. The measurements for the wiggler mockup show that our short-period wiggler performance include peak value of magnetic field BW=0.35T with it' s period λW= 10mm and space between magnets δ = 5mm, relative maxium deviation of magnetic field δBW/B≤ 1.25%.
The design of a high performance short-period wiggler is introduced, Tunableness to magnetic field in half period length has been achieved by slot location of separate permanent magnet. The measurements for the wiggler mockup show that our short-period wiggler performance include peak value of magnetic field BW=0.35T with it' s period λW= 10mm and space between magnets δ = 5mm, relative maxium deviation of magnetic field δBW/B≤ 1.25%.
