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RSS2002 Vol. 14, No. 06
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2002,
14.
Abstract:
Experimental study on hard Xray generation was carried out on Ｆlash 2 accelerator, with the method of REB transported in a low pressure gas via azimuthal magnetic field and interacted with Ta target. At 47cm transporting distance, the measured areal integral of hard Xray dose rate was 2.1×１０１０Gy·cm2/s,total areal integral of hard X-ray dose was 1 843Gy·cm2, and Xray convert rate was 108Gy·cm2/kJ．
Experimental study on hard Xray generation was carried out on Ｆlash 2 accelerator, with the method of REB transported in a low pressure gas via azimuthal magnetic field and interacted with Ta target. At 47cm transporting distance, the measured areal integral of hard Xray dose rate was 2.1×１０１０Gy·cm2/s,total areal integral of hard X-ray dose was 1 843Gy·cm2, and Xray convert rate was 108Gy·cm2/kJ．
2002,
14.
Abstract:
Based on the principle of coupling impedance bench measurement, the validity of this method is discussed by simulation method in this paper. Beginning with the analysis of electromagnetic field in homogeneous circular waveguide and coaxial transmission line, the physical concept and source of validity question of coaxialwire method are described and a general conclusion is obtained. Then some results obtained by other methods are reviewed briefly. Finally, the simulation method to analyze the validity problem and the main results are presented. The simulation method can not only be applied to most accelerator components, but also give more precise and direct results.
Based on the principle of coupling impedance bench measurement, the validity of this method is discussed by simulation method in this paper. Beginning with the analysis of electromagnetic field in homogeneous circular waveguide and coaxial transmission line, the physical concept and source of validity question of coaxialwire method are described and a general conclusion is obtained. Then some results obtained by other methods are reviewed briefly. Finally, the simulation method to analyze the validity problem and the main results are presented. The simulation method can not only be applied to most accelerator components, but also give more precise and direct results.
2002,
14.
Abstract:
We analysis the wakefield generation and the electrons acceleration when ultraintense short laser pulse propagate through tenuous plasma with 2D3V PIC simulation model．The effects of FRS elongates the length of the laser pulse as well as steeps the tail of the pulse which results in the notable reduces of the electrostatic phase velocity and maximum electron kinetic energy achieved when traped．At the same time the most effective length of the laser pulse to stimulate the wake-field becomes longer.
We analysis the wakefield generation and the electrons acceleration when ultraintense short laser pulse propagate through tenuous plasma with 2D3V PIC simulation model．The effects of FRS elongates the length of the laser pulse as well as steeps the tail of the pulse which results in the notable reduces of the electrostatic phase velocity and maximum electron kinetic energy achieved when traped．At the same time the most effective length of the laser pulse to stimulate the wake-field becomes longer.
2002,
14.
Abstract:
The damage reason of an anode tungstenmesh is analyzed by scanning electron mirror and experiments. When a tungstenmesh is quenchtreated, an oxidizedlayer forms on its surface and the life of the tungstenmesh increases obviously. Auger effect spectrum of tungstenmesh samples shows that the thickness of the oxidizedlayer changes with quenchtreated temperature. The experimental results show that the thickness of the oxidizedlayer obviously affects the life of tungstenmesh. The optimum thickness of the oxidizedlayer is about 400nm when a 90ns(FWHM), 6kA, 1MeV beam passes through the tungstenmesh.
The damage reason of an anode tungstenmesh is analyzed by scanning electron mirror and experiments. When a tungstenmesh is quenchtreated, an oxidizedlayer forms on its surface and the life of the tungstenmesh increases obviously. Auger effect spectrum of tungstenmesh samples shows that the thickness of the oxidizedlayer changes with quenchtreated temperature. The experimental results show that the thickness of the oxidizedlayer obviously affects the life of tungstenmesh. The optimum thickness of the oxidizedlayer is about 400nm when a 90ns(FWHM), 6kA, 1MeV beam passes through the tungstenmesh.
2002,
14.
Abstract:
Based on nonlinear feedback control method, waveletbased feedback controller as a especial nonlinear feedback function is designed for controlling beam halochaos in highcurrent accelerators of driven clean nuclear power system. In this article, PIC simulations show that suppression of beam halochaos are realized effectively after discrete control of waveletbased feedback is applied to five kinds of the initial proton beam distributions, respectively. The beam halo strength factor is quickly reduced to zero, and other statistical physical quantities of beam halochaos are more than doubly reduced. These performed PIC simulation results demonstrate that the developed methods are very effective for control of beam halochaos. Potential application of the beam halochaos control m
Based on nonlinear feedback control method, waveletbased feedback controller as a especial nonlinear feedback function is designed for controlling beam halochaos in highcurrent accelerators of driven clean nuclear power system. In this article, PIC simulations show that suppression of beam halochaos are realized effectively after discrete control of waveletbased feedback is applied to five kinds of the initial proton beam distributions, respectively. The beam halo strength factor is quickly reduced to zero, and other statistical physical quantities of beam halochaos are more than doubly reduced. These performed PIC simulation results demonstrate that the developed methods are very effective for control of beam halochaos. Potential application of the beam halochaos control m
2002,
14.
Abstract:
An electronbeam Teslatransformer accelerator is described. It consists of the primary storage energy system, Tesla transformer, oil Blumlein pulse form line, and the vacuum diode. The experiments of initial stage showed that diode voltage rises up to about 500kV with an input of 20kV and the maximum electronbean current is about 9kA, the pulse width is about 50ns. This device can operate stably and be set up easily．
An electronbeam Teslatransformer accelerator is described. It consists of the primary storage energy system, Tesla transformer, oil Blumlein pulse form line, and the vacuum diode. The experiments of initial stage showed that diode voltage rises up to about 500kV with an input of 20kV and the maximum electronbean current is about 9kA, the pulse width is about 50ns. This device can operate stably and be set up easily．
2002,
14.
Abstract:
The experiments on the IGBT solid state switch for induction accelerator was carried out with two series 1.2kV, 75A IGBT (GA75TS120U). The static and dynamic balancing modules were carried out with metal oxide varistores, capacities and diodes in order to suppress the overvoltage during IGBT on and off. Experimental results show that IGBT solid state switch works very stable under the different conditions. It can output peak voltage 1.8kV, rise time 300ns, fall time 1.64μs waveforms on the loads. The simulation data using OrCAD are in accord with experimental results except the rise time.
The experiments on the IGBT solid state switch for induction accelerator was carried out with two series 1.2kV, 75A IGBT (GA75TS120U). The static and dynamic balancing modules were carried out with metal oxide varistores, capacities and diodes in order to suppress the overvoltage during IGBT on and off. Experimental results show that IGBT solid state switch works very stable under the different conditions. It can output peak voltage 1.8kV, rise time 300ns, fall time 1.64μs waveforms on the loads. The simulation data using OrCAD are in accord with experimental results except the rise time.
2002,
14.
Abstract:
The requirements of magnetic material in linac induction accelerator and the characteristics of amorphous and ferrite are described briefly in this paper. Some instances about using amorphous to replace ferrite material are reviewed in the paper too. Experimentations are carried out under static condition, in additional more researches are done based on pulse condition. It is concluded that both materials have higher satutration magnetic density under pulse condition than under static condition.
The requirements of magnetic material in linac induction accelerator and the characteristics of amorphous and ferrite are described briefly in this paper. Some instances about using amorphous to replace ferrite material are reviewed in the paper too. Experimentations are carried out under static condition, in additional more researches are done based on pulse condition. It is concluded that both materials have higher satutration magnetic density under pulse condition than under static condition.
2002,
14.
Abstract:
A radial insulation structure which is used in long pulse high current diode is introduced in this paper. The theory of vacuum flashover and the idea of design are briefly introduced. In the research, coneshaped insulator was used. The geometry structure parameters were optimized by simulating the static electrical field distribution. Experiment was done on a pulse power source with 200ns pulse width. The maximum voltage 750kV was obtained, and the average standoff electrical field of insulator is about 50kV/cm.
A radial insulation structure which is used in long pulse high current diode is introduced in this paper. The theory of vacuum flashover and the idea of design are briefly introduced. In the research, coneshaped insulator was used. The geometry structure parameters were optimized by simulating the static electrical field distribution. Experiment was done on a pulse power source with 200ns pulse width. The maximum voltage 750kV was obtained, and the average standoff electrical field of insulator is about 50kV/cm.
2002,
14.
Abstract:
An experimental setup is developed to measure the characteristics of semiconductor opening switch (SOS). The parameters, such as interruption impedance, current interruption time, voltage gain, pulse duration and energy transfer efficiency, are studied experimentally. The experimental results show that forward pumping time and reverse pumping time are important parameters for semiconductor opening switches. The influences of forward pumping time and reverse pumping time on interruption time, voltage gain, and energy transfer efficiency are obtained. In the interruption process, the impedance variation is divided into three phases: that is rapid increasing phase, slow change phase and completely interruption phase.
An experimental setup is developed to measure the characteristics of semiconductor opening switch (SOS). The parameters, such as interruption impedance, current interruption time, voltage gain, pulse duration and energy transfer efficiency, are studied experimentally. The experimental results show that forward pumping time and reverse pumping time are important parameters for semiconductor opening switches. The influences of forward pumping time and reverse pumping time on interruption time, voltage gain, and energy transfer efficiency are obtained. In the interruption process, the impedance variation is divided into three phases: that is rapid increasing phase, slow change phase and completely interruption phase.
2002,
14.
Abstract:
In this paper, a new high power solidstate laser multisegmentamplifier pumped with flashlamps with 29cm×29cm aperture has been tested. Under the condition of charge voltage of 23kV and pumping energy density of 10J/cm3, the end module small signal gain coefficient of 4.925%cm-1 and the interior module small signal gain coefficient of 5.519%cm-1 in full aperture were obtained in experiments.
In this paper, a new high power solidstate laser multisegmentamplifier pumped with flashlamps with 29cm×29cm aperture has been tested. Under the condition of charge voltage of 23kV and pumping energy density of 10J/cm3, the end module small signal gain coefficient of 4.925%cm-1 and the interior module small signal gain coefficient of 5.519%cm-1 in full aperture were obtained in experiments.
2002,
14.
Abstract:
The multifilms targets are often used in the studies of ICF experiment and astrophysical opacity. One of the methods producing these targets is the Pulse Laser Deposition (PLD) technology. In this paper, the principle of PLD technology, experiment method, PLD equipment design and the application in fabrication of the ICF filmtargets have been described in detail. Using PLD method, the Cu films and Cu/Fe films were been produced. The average roughness of Cu films is 0.2nm and Cu/Fe films is 0.4nm. Experiments shown that the equipment and the methods were suitable.
The multifilms targets are often used in the studies of ICF experiment and astrophysical opacity. One of the methods producing these targets is the Pulse Laser Deposition (PLD) technology. In this paper, the principle of PLD technology, experiment method, PLD equipment design and the application in fabrication of the ICF filmtargets have been described in detail. Using PLD method, the Cu films and Cu/Fe films were been produced. The average roughness of Cu films is 0.2nm and Cu/Fe films is 0.4nm. Experiments shown that the equipment and the methods were suitable.
2002,
14.
Abstract:
Ｔhe equations of onedimensional threetemperature radiation magnetohydrodynamics, which are to describe the plasma process of Zpinch, were set up under Largrangian coordinates. The Al wirearray Z-pinch experiment on Saturn in Sandia laboratory in USA, was simulated using our onedimensional lagrangian code based on the equations. The reasonable and selfconsistent spatiotemporal distributions of all plasma parameters in the process were obtained. The time and velocity of Zpinch plasma to center, pulse width and energy of Xray radiated by the Zpinch plasma are basically agreed with the experimental results on Saturn. The results suggested that the equations and its code are correct.
Ｔhe equations of onedimensional threetemperature radiation magnetohydrodynamics, which are to describe the plasma process of Zpinch, were set up under Largrangian coordinates. The Al wirearray Z-pinch experiment on Saturn in Sandia laboratory in USA, was simulated using our onedimensional lagrangian code based on the equations. The reasonable and selfconsistent spatiotemporal distributions of all plasma parameters in the process were obtained. The time and velocity of Zpinch plasma to center, pulse width and energy of Xray radiated by the Zpinch plasma are basically agreed with the experimental results on Saturn. The results suggested that the equations and its code are correct.
2002,
14.
Abstract:
A new mirror frame structure is described in this paper. This mirror structure uses single frame, which based on one point and adjusted in two points for two angle adjustment. This mirror with new structure has many advantages:simple structure, small capacity, high sensitivity, high stability and can be used in different elevations. An important characteristic of this new mirror structure is that it can be used in array cavity mirror and array transmitting mirror for ICF. The specimens of single mirror with new frame structure, array cavity mirror and array transmitting mirror consisted of the mirrors and the results of their testing are given in this paper.
A new mirror frame structure is described in this paper. This mirror structure uses single frame, which based on one point and adjusted in two points for two angle adjustment. This mirror with new structure has many advantages:simple structure, small capacity, high sensitivity, high stability and can be used in different elevations. An important characteristic of this new mirror structure is that it can be used in array cavity mirror and array transmitting mirror for ICF. The specimens of single mirror with new frame structure, array cavity mirror and array transmitting mirror consisted of the mirrors and the results of their testing are given in this paper.
2002,
14.
Abstract:
The radiation ablation experiments of CH foils are simulated using the experiment radiation flow in the hohlraum by 1 D radiation transfer code RDMG. The results of simulation show that influence of NonLTE radiation source on the ablation of CH foil is very obvious. The results of simulation and experiment including radiation flow total intensity and the variation of radiation temperature with time at the rear of CH foil, as well as the time delay of 400eV photon arriving at the rear of CH foil are consistent basically.
The radiation ablation experiments of CH foils are simulated using the experiment radiation flow in the hohlraum by 1 D radiation transfer code RDMG. The results of simulation show that influence of NonLTE radiation source on the ablation of CH foil is very obvious. The results of simulation and experiment including radiation flow total intensity and the variation of radiation temperature with time at the rear of CH foil, as well as the time delay of 400eV photon arriving at the rear of CH foil are consistent basically.
2002,
14.
Abstract:
In order to explore a method to characterize the service behavior of thermal control coatings in geostationary earth orbit (GEO), evolution in optical properties of Teflon FEP/Al second surface mirror was investigated in the conditions of independent radiation with electrons and/or protons and combined radiation with electrons with solar electromagnetic rays. Experimental results show that the electron radiation would result in an accumulation of negative charges on the surface of Teflon FEP/Al coatings, which might obstruct the experimental results and can be reduced to a quite extent by the simultaneous radiation of solar electromagnetic rays. Under the condition of the same multiplier values of fluence and energy (φE), the increment of solar absorptance (Δas) of Teflon FEP/Al coatings
In order to explore a method to characterize the service behavior of thermal control coatings in geostationary earth orbit (GEO), evolution in optical properties of Teflon FEP/Al second surface mirror was investigated in the conditions of independent radiation with electrons and/or protons and combined radiation with electrons with solar electromagnetic rays. Experimental results show that the electron radiation would result in an accumulation of negative charges on the surface of Teflon FEP/Al coatings, which might obstruct the experimental results and can be reduced to a quite extent by the simultaneous radiation of solar electromagnetic rays. Under the condition of the same multiplier values of fluence and energy (φE), the increment of solar absorptance (Δas) of Teflon FEP/Al coatings
2002,
14.
Abstract:
The semiinsulating GaAs photoconductive switches, whose deep energy defect is introduced by particle beam irradiation, are described. The experiments of two kinds of switches with the distance of 3mm and 8mm between two electrodes respectively, triggered by infrared laser pulse are reported, and the photon energy of the trigger laser is lower than the GaAs bandgap. The output electronic pulse whose repetition rates are 5kHz and 20MHz are observed when triggered by 900nm diode laser and 1 530nm optical fiber laser respectively. The semiinsulating GaAs photoconductive switch can operate in linear mode and nonlinear mode respectively, when they are switched at 3kV and 5kV and triggered by 1 064nm Nd:YAG laser with the energy of 1.9mJ. The experiments indicated the semiinsulating GaAs ph
The semiinsulating GaAs photoconductive switches, whose deep energy defect is introduced by particle beam irradiation, are described. The experiments of two kinds of switches with the distance of 3mm and 8mm between two electrodes respectively, triggered by infrared laser pulse are reported, and the photon energy of the trigger laser is lower than the GaAs bandgap. The output electronic pulse whose repetition rates are 5kHz and 20MHz are observed when triggered by 900nm diode laser and 1 530nm optical fiber laser respectively. The semiinsulating GaAs photoconductive switch can operate in linear mode and nonlinear mode respectively, when they are switched at 3kV and 5kV and triggered by 1 064nm Nd:YAG laser with the energy of 1.9mJ. The experiments indicated the semiinsulating GaAs ph
2002,
14.
Abstract:
High-order harmonic generation by relativistic lasers in plasmas with initial velocity distribution has been studied. It is shown that, different from previous models, because of the random thermal motion of electrons, the initially Maxwellian distributed plasma will make the harmonic spectrum more smooth, i.e., it increases the higher-order harmonic power but decreases the lower-order harmonic power. This effect is beneficial for the generation of higherorder harmonics．
High-order harmonic generation by relativistic lasers in plasmas with initial velocity distribution has been studied. It is shown that, different from previous models, because of the random thermal motion of electrons, the initially Maxwellian distributed plasma will make the harmonic spectrum more smooth, i.e., it increases the higher-order harmonic power but decreases the lower-order harmonic power. This effect is beneficial for the generation of higherorder harmonics．
2002,
14.
Abstract:
The nonlinear laser beam propagation in high power laser driver and the influence of the smallscale selffocusing and phase noise on beam quality in disk amplifier have been analyzed by a linear model. The quantitative relations between intensities of phase noise, Bintegral, and the beam intensity contrast in near field are given explicitly. A spectrum specification of phase noise can be given when modulation contrast of output beam is very small.
The nonlinear laser beam propagation in high power laser driver and the influence of the smallscale selffocusing and phase noise on beam quality in disk amplifier have been analyzed by a linear model. The quantitative relations between intensities of phase noise, Bintegral, and the beam intensity contrast in near field are given explicitly. A spectrum specification of phase noise can be given when modulation contrast of output beam is very small.
2002,
14.
Abstract:
A continuous wave DF laser was induced on the PV HgCdTe infrared detectors, under various power density ,the detectors had a serious of output. With the increasing of irradiated laser power density, firstly the detector worked in linear section, then chaos occurred (laser power density about 334mW/cm2) , lastly unstable detector homopolarization was observed(laser power density about 14W/cm2),and the detector recovered to normal working status after the laser was removed. Some explanations about the results were given, as the results were very different from the theoretic expectation, they provide valuable clue for future research on PV HgCdTe.
A continuous wave DF laser was induced on the PV HgCdTe infrared detectors, under various power density ,the detectors had a serious of output. With the increasing of irradiated laser power density, firstly the detector worked in linear section, then chaos occurred (laser power density about 334mW/cm2) , lastly unstable detector homopolarization was observed(laser power density about 14W/cm2),and the detector recovered to normal working status after the laser was removed. Some explanations about the results were given, as the results were very different from the theoretic expectation, they provide valuable clue for future research on PV HgCdTe.
2002,
14.
Abstract:
A numerical model of atmospheric optical refractive index structure parameter is presented. This model solves the set of prognostic equations of horizontal components of the wind, the potential temperature, specific humidity, an energy balance equation, and a soil heat conduction equation, to obtain the ground surface temperature, the surface flux of momentum, sensible heat, and latent heat. These fluxes are then used to calculate refractive index structure parameter by empirical relationships of turbulence flux and temperature structure parameter according to MoninObukhov similarity theory.
A numerical model of atmospheric optical refractive index structure parameter is presented. This model solves the set of prognostic equations of horizontal components of the wind, the potential temperature, specific humidity, an energy balance equation, and a soil heat conduction equation, to obtain the ground surface temperature, the surface flux of momentum, sensible heat, and latent heat. These fluxes are then used to calculate refractive index structure parameter by empirical relationships of turbulence flux and temperature structure parameter according to MoninObukhov similarity theory.
2002,
14.
Abstract:
This paper calculates the allowing angle of interaction of three waves in KTP crystal in smallsignal proximity. It gets the change of allowing angle with output wavelength and the crystal length. And the tuning curves of KTPOPO, which pumped by Nd:YAG laser(1 064nm), are calculated. Furthermore, it also discusses the influence of mismatching angle on phase mismatching coefficient at various output wavelengths and in the same tuning precision the influence of the crystal length on efficiency. The results provide some theoretical references for optimized design of infrared tunable OPO.
This paper calculates the allowing angle of interaction of three waves in KTP crystal in smallsignal proximity. It gets the change of allowing angle with output wavelength and the crystal length. And the tuning curves of KTPOPO, which pumped by Nd:YAG laser(1 064nm), are calculated. Furthermore, it also discusses the influence of mismatching angle on phase mismatching coefficient at various output wavelengths and in the same tuning precision the influence of the crystal length on efficiency. The results provide some theoretical references for optimized design of infrared tunable OPO.
2002,
14.
Abstract:
A mathematical model of laser compensation propagation process by combining the stimulated Brillouinscattering (SBS) and laser propagation in the atmosphere is constructed and the numerical simulation is also conducted. On the basis of realizing a beacon of a small area on an uncooperative and extensive target with SBS threshold, we presented and demonstrated the feasibility of the method to actively obtain the phaseconjugatelight on the target. The experiments of laser propagation with SBS are conducted in case of a 250m distance, which shows that by utilizing the SBS threshold effect the small area beacon could be obtained on the target actively.
A mathematical model of laser compensation propagation process by combining the stimulated Brillouinscattering (SBS) and laser propagation in the atmosphere is constructed and the numerical simulation is also conducted. On the basis of realizing a beacon of a small area on an uncooperative and extensive target with SBS threshold, we presented and demonstrated the feasibility of the method to actively obtain the phaseconjugatelight on the target. The experiments of laser propagation with SBS are conducted in case of a 250m distance, which shows that by utilizing the SBS threshold effect the small area beacon could be obtained on the target actively.
2002,
14.
Abstract:
Using the Cr4+:Nd3＋:YAG microchip pumped by LD, the self Qswitched laser pulses with the repetition rate of 2.78kHz and pulse width of 6ns are obtained in the CW case. Through the pre-pumping with the pulsed modulated current the self Qswitched output laser with a controllable repetition rate is realized. Compare with the extra-cavity selfQswitched microchip laser the monolithic microchip laser possess higher transform efficiency, more narrow pulse width and high repetition rate. Also such a laser constructed compact and easy to be adjusted．
Using the Cr4+:Nd3＋:YAG microchip pumped by LD, the self Qswitched laser pulses with the repetition rate of 2.78kHz and pulse width of 6ns are obtained in the CW case. Through the pre-pumping with the pulsed modulated current the self Qswitched output laser with a controllable repetition rate is realized. Compare with the extra-cavity selfQswitched microchip laser the monolithic microchip laser possess higher transform efficiency, more narrow pulse width and high repetition rate. Also such a laser constructed compact and easy to be adjusted．
2002,
14.
Abstract:
A package structure of high power linear array diode laser (DL) with 940nm wavelength was designed using active cooling way by which, the cooler was made by line cutting with simply long water cooler, Its thermal resistance was measured as 0.45℃/W. Experiment was carried out. in which the packaged DL laser power reached 40W when continuously work, and its peak power reached 100W at 100Hz frequency and 50μs pulse width.When the pulse width increased to 200μs, its laser power decreased to 103W．
A package structure of high power linear array diode laser (DL) with 940nm wavelength was designed using active cooling way by which, the cooler was made by line cutting with simply long water cooler, Its thermal resistance was measured as 0.45℃/W. Experiment was carried out. in which the packaged DL laser power reached 40W when continuously work, and its peak power reached 100W at 100Hz frequency and 50μs pulse width.When the pulse width increased to 200μs, its laser power decreased to 103W．
2002,
14.
Abstract:
With the development of the study on laser induced damage threshold testing for optics, many factors need to be considered in measuring and showing the LIDT efficiently and accurately. In this paper, R to 1 test method was used in the laserinduced damage testing under different beam diameter. The new concept of R to 1 average damage threshold was used. The relationship between damage threshold and testing beam diameter was discussed. It shows that laser induced damage threshold continuously decreases as the testing beam diameter increases. When the testing beam diameter increases to a certain value, LIDT tends to be invariable.
With the development of the study on laser induced damage threshold testing for optics, many factors need to be considered in measuring and showing the LIDT efficiently and accurately. In this paper, R to 1 test method was used in the laserinduced damage testing under different beam diameter. The new concept of R to 1 average damage threshold was used. The relationship between damage threshold and testing beam diameter was discussed. It shows that laser induced damage threshold continuously decreases as the testing beam diameter increases. When the testing beam diameter increases to a certain value, LIDT tends to be invariable.
2002,
14.
Abstract:
Mathematical model based on spontaneous emission and shotnoise of SASE FEL is introduced. A detailed study of startup and statistical properties of the radiation from a SASE FEL operating has been performed by means of the modified 1D timedependent FEL code. It is shown that the width of the radiation spectrum becomes at first narrow then broad. After several gain lengths the spectrum transforms into that of the high gain FEL amplifier. The statistical properties of the radiation have been proved that finitetime integrals of the instantaneous power follow a gamma distribution.
Mathematical model based on spontaneous emission and shotnoise of SASE FEL is introduced. A detailed study of startup and statistical properties of the radiation from a SASE FEL operating has been performed by means of the modified 1D timedependent FEL code. It is shown that the width of the radiation spectrum becomes at first narrow then broad. After several gain lengths the spectrum transforms into that of the high gain FEL amplifier. The statistical properties of the radiation have been proved that finitetime integrals of the instantaneous power follow a gamma distribution.
2002,
14.
Abstract:
Scanning time and scanning velocity of high speed imageconverter camera were calibrated by applying ps pulse laser and high precise delay trigger. The precision requirement of calibrating devices and calibrating method，results of calibration and measurement uncertainty were given. The formulas of scanning time and scanning velocity according to image position were fitted，which provided dependable basis for data processing．
Scanning time and scanning velocity of high speed imageconverter camera were calibrated by applying ps pulse laser and high precise delay trigger. The precision requirement of calibrating devices and calibrating method，results of calibration and measurement uncertainty were given. The formulas of scanning time and scanning velocity according to image position were fitted，which provided dependable basis for data processing．
2002,
14.
Abstract:
The scale law and design procedure of the high power FEL are discussed. It is pointed out that the extraction efficiency which is the critical factor of the output power besides the power of the electron beam is uniquely determined by the number of wiggler period and has almost nothing to do with other parameters of FEL such as period and normalized strength of wiggler and laser wavelength.
The scale law and design procedure of the high power FEL are discussed. It is pointed out that the extraction efficiency which is the critical factor of the output power besides the power of the electron beam is uniquely determined by the number of wiggler period and has almost nothing to do with other parameters of FEL such as period and normalized strength of wiggler and laser wavelength.
2002,
14.
Abstract:
The hybrid model for analyzing the helix tape considering its radial thickness is developed in this paper. In the hybrid model, by expanding the surface currents on the helix tape in a series of Chebyshev polynomials, simulating the helical thickness with vacuum layer and equaling the rods with multiple azimuthally symmetric layers, the dispersion equation and interaction impedance of helical slow wave structure with arbitrary tape width, supported by a radially stratified dielectric layer and enclosed by a metallic shell are obtained. The calculating results using hybrid model presented in the paper show good agreement with the experiment results.
The hybrid model for analyzing the helix tape considering its radial thickness is developed in this paper. In the hybrid model, by expanding the surface currents on the helix tape in a series of Chebyshev polynomials, simulating the helical thickness with vacuum layer and equaling the rods with multiple azimuthally symmetric layers, the dispersion equation and interaction impedance of helical slow wave structure with arbitrary tape width, supported by a radially stratified dielectric layer and enclosed by a metallic shell are obtained. The calculating results using hybrid model presented in the paper show good agreement with the experiment results.
2002,
14.
Abstract:
Based on the theory of mode coupling, this paper discusses the circular waveguide mode conversion with waveguide axis curved and radius tapered in detail. It also carries out the optimized analysis about the geometry structure of TE0nTE11 mode converter. Adopting different phase rematch techniques, the optimal geometry parameter is obtained. The mode converter designed in this way owns high conversion efficiency exceeding 98%.
Based on the theory of mode coupling, this paper discusses the circular waveguide mode conversion with waveguide axis curved and radius tapered in detail. It also carries out the optimized analysis about the geometry structure of TE0nTE11 mode converter. Adopting different phase rematch techniques, the optimal geometry parameter is obtained. The mode converter designed in this way owns high conversion efficiency exceeding 98%.
2002,
14.
Abstract:
Designing an octave bandwidth helical traveling wave tube for phase and gain matched operation in the EHF region presents many obstacles, the dimensional controls must be imposed in the design. In this paper, a code is programmed based on the sheath model. In the sheath model the helix is approximated by a helically conducting cylindrical surface of negligible thickness. The code is used to determine the effect on dispersion and onaxis interaction impedance of several helical slowwave circuit parameter variations, including thickness and relative dielectric constant of the support rods, pitch width, height of the metal vane and helix average radius. The specific results can serve as a general guide for similar devices, and the computational techniques are readily applicable to other TW
Designing an octave bandwidth helical traveling wave tube for phase and gain matched operation in the EHF region presents many obstacles, the dimensional controls must be imposed in the design. In this paper, a code is programmed based on the sheath model. In the sheath model the helix is approximated by a helically conducting cylindrical surface of negligible thickness. The code is used to determine the effect on dispersion and onaxis interaction impedance of several helical slowwave circuit parameter variations, including thickness and relative dielectric constant of the support rods, pitch width, height of the metal vane and helix average radius. The specific results can serve as a general guide for similar devices, and the computational techniques are readily applicable to other TW
2002,
14.
Abstract:
This paper presents the progress on an Lband long pulse relativistic klystron amplifier. Modulation of IREB through the idler cavity gap and microwave extraction from the modulated IREB are described in detail. The problem of beamcurrentpulseshortening through the idler cavity gap is solved to a certain extent as well as the problem of output microwave pulseshortening, and highmodulated IREB are obtained after parameter adjustment on the input microwave and the idler cavity. In the experiment, the 446kV/ 30kA/1.4μs hollow electron beams generated about 2.0kA/1.0μs modulated current after two idler cavity gaps. They got more than 381MW/200ns RF power with the new output cavity loaded Q of about 7.9. The efficiency is 28%, and the gain is 34dB.
This paper presents the progress on an Lband long pulse relativistic klystron amplifier. Modulation of IREB through the idler cavity gap and microwave extraction from the modulated IREB are described in detail. The problem of beamcurrentpulseshortening through the idler cavity gap is solved to a certain extent as well as the problem of output microwave pulseshortening, and highmodulated IREB are obtained after parameter adjustment on the input microwave and the idler cavity. In the experiment, the 446kV/ 30kA/1.4μs hollow electron beams generated about 2.0kA/1.0μs modulated current after two idler cavity gaps. They got more than 381MW/200ns RF power with the new output cavity loaded Q of about 7.9. The efficiency is 28%, and the gain is 34dB.
2002,
14.
Abstract:
When using the finitedifference timedomain (FDTD) method to solve the electromagnetic problems, the locally conformal grids are often chosen to conform the shape of the boundary such as a curved or slant plane. Pentagonal conformal grids modeling in the twodimensional cylindrical coordinate are specially discussed in this paper. This model is available not only to the perfectly electrically conducting boundary but also to the more complex structures such as the slant thin material sheets and the uneven specific conductance slant materials. The reflection from the pec conical antenna and the farzone radiated waveform from the resistiveloaded conical antenna are taken as examples to validate the effectiveness of the modeling, and the results are good.
When using the finitedifference timedomain (FDTD) method to solve the electromagnetic problems, the locally conformal grids are often chosen to conform the shape of the boundary such as a curved or slant plane. Pentagonal conformal grids modeling in the twodimensional cylindrical coordinate are specially discussed in this paper. This model is available not only to the perfectly electrically conducting boundary but also to the more complex structures such as the slant thin material sheets and the uneven specific conductance slant materials. The reflection from the pec conical antenna and the farzone radiated waveform from the resistiveloaded conical antenna are taken as examples to validate the effectiveness of the modeling, and the results are good.
2002,
14.
Abstract:
There are various kinds of HEMP environment definitions. The coupling effects of electronic system are more different under different HEMP environment. In this paper, the responds of cable of different length are investigated under 1976 HEMP and 1996 HEMP environment. The results indicate that the cable coupling effects under 1976 HEMP environment are more serious than those under 1996 HEMP environment.
There are various kinds of HEMP environment definitions. The coupling effects of electronic system are more different under different HEMP environment. In this paper, the responds of cable of different length are investigated under 1976 HEMP and 1996 HEMP environment. The results indicate that the cable coupling effects under 1976 HEMP environment are more serious than those under 1996 HEMP environment.
2002,
14.
Abstract:
The vaneloaded helical slowwave structure is widely used in high power, broadband travelingwave tube(TWT). The tape helix model is suggested for vaneloaded helical slowwave structures in this paper. And the dispersion equations, the expressions of interaction impedance and attenuation constant are obtained. Some helical slowwave structures of TWT are calculated by the derived equations and sheath model. The calculated results accord with measured values very well. The influence on dispersion characteristics is analyzed for different radius of metal envelope.
The vaneloaded helical slowwave structure is widely used in high power, broadband travelingwave tube(TWT). The tape helix model is suggested for vaneloaded helical slowwave structures in this paper. And the dispersion equations, the expressions of interaction impedance and attenuation constant are obtained. Some helical slowwave structures of TWT are calculated by the derived equations and sheath model. The calculated results accord with measured values very well. The influence on dispersion characteristics is analyzed for different radius of metal envelope.
2002,
14.
Abstract:
The computational simulation for highfrequency characteristic of helical slowwave circuit using MAFIA software avoids the assumptive theory conditions, improving the calculation precision. Compared with the experiment data, the average error of dispersion simulation result reachs less than 1%, and that of impedance reachs less than 0.2%. Compared with the calculation time and precision using the different simulation method in the different modeling method, the quasiperiodic boundary conditions is proved a simulation method of satisfying precision and efficiency demand in practical engineering application.
The computational simulation for highfrequency characteristic of helical slowwave circuit using MAFIA software avoids the assumptive theory conditions, improving the calculation precision. Compared with the experiment data, the average error of dispersion simulation result reachs less than 1%, and that of impedance reachs less than 0.2%. Compared with the calculation time and precision using the different simulation method in the different modeling method, the quasiperiodic boundary conditions is proved a simulation method of satisfying precision and efficiency demand in practical engineering application.
