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RSS1999 Vol. 11, No. 04
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1999,
11.
Abstract:
An overview is given of th e concept and basic properties relevant to the laser wakefield accelerator, the plasma beatwave accelerator, wakefield accelerators driven by multiple laser pulses, and selfmodulated laser wakefield accelerator. Recent e xperimental results are also summarized. Generation mechanism of plasma wave is introduced, as well as the trapping and acceleration of electrons in the plasma wave. Some limits on laserplasma accelerators are discussed associated with th e future prospect of laserplasma accelerators.
An overview is given of th e concept and basic properties relevant to the laser wakefield accelerator, the plasma beatwave accelerator, wakefield accelerators driven by multiple laser pulses, and selfmodulated laser wakefield accelerator. Recent e xperimental results are also summarized. Generation mechanism of plasma wave is introduced, as well as the trapping and acceleration of electrons in the plasma wave. Some limits on laserplasma accelerators are discussed associated with th e future prospect of laserplasma accelerators.
1999,
11.
Abstract:
The physical scheme in３ｄ５／２２ｐ３／２ transition in Hlike C ionproduced from Zpinc h carbon plasma has been studied using a onedimensional Lagrangian MHD code co upled to an atomic kinetic code.The three phases, i.e., runin phase, stagnati on thase and runout phase,were discussed, respectively. As results from discu ssion, C plasma should be intermingled with inert gas so that the electron density at stagnation isn't too high, the time when plasma enters into runout phase should be latter than the peak time of current, and the initial plasma density in the capillary should be low enough so that the required capillary radius is not too small.
The physical scheme in３ｄ５／２２ｐ３／２ transition in Hlike C ionproduced from Zpinc h carbon plasma has been studied using a onedimensional Lagrangian MHD code co upled to an atomic kinetic code.The three phases, i.e., runin phase, stagnati on thase and runout phase,were discussed, respectively. As results from discu ssion, C plasma should be intermingled with inert gas so that the electron density at stagnation isn't too high, the time when plasma enters into runout phase should be latter than the peak time of current, and the initial plasma density in the capillary should be low enough so that the required capillary radius is not too small.
1999,
11.
Abstract:
The threshold of parametric inst abilities will be increased and the growth rate will fall down if the coherence time of pump laser is less than the rise time of parametric instabilities. The paper shows the finitebandwidth effect of reduction in parametric instabilitie s and superathermal electrons using chirped stretched laser pulse. Both analytical solutions and the results of numerical simulation using PIC code are presented.The effect of electronion collision on suprathermal electrons is also investigated.
The threshold of parametric inst abilities will be increased and the growth rate will fall down if the coherence time of pump laser is less than the rise time of parametric instabilities. The paper shows the finitebandwidth effect of reduction in parametric instabilitie s and superathermal electrons using chirped stretched laser pulse. Both analytical solutions and the results of numerical simulation using PIC code are presented.The effect of electronion collision on suprathermal electrons is also investigated.
1999,
11.
Abstract:
Based on the motion of t he single electron whose incident phase is φ0 in standing wave electric field under the small signal condition,the transittime effect of electron be am in π mode standing wave electric field in the threecavity resonator is investigated, the expressions of electron load conductance in the threecavity resonator are presented ,and the beamwave energy interchange in the threecavity resonator is discussed．
Based on the motion of t he single electron whose incident phase is φ0 in standing wave electric field under the small signal condition,the transittime effect of electron be am in π mode standing wave electric field in the threecavity resonator is investigated, the expressions of electron load conductance in the threecavity resonator are presented ,and the beamwave energy interchange in the threecavity resonator is discussed．
1999,
11.
Abstract:
Some important concepts relating to the flattened Gaussian beams(FGBs),such as the field distribution and beam width, are analyzed physically. The twodimensional(2D) FGB is extended to the threedimensional(3D) case,and the 3D symmetrical transformations, inclu ding equal beam widths in x and y dimensions and equal curvature radii at a z plane, are studied in detail.
Some important concepts relating to the flattened Gaussian beams(FGBs),such as the field distribution and beam width, are analyzed physically. The twodimensional(2D) FGB is extended to the threedimensional(3D) case,and the 3D symmetrical transformations, inclu ding equal beam widths in x and y dimensions and equal curvature radii at a z plane, are studied in detail.
1999,
11.
Abstract:
Third harmonic generation (THG) of Ti:sapphire 744nm laser is produced using two pieces of type Ⅰ BBO crystal while rotating the cardinal plane of the crystal. The relationship between the THG laser energy and the rotate angle is investigated in theory and experiment, the temporal and spatial characters of ω, 2ω, 3ω of output are detected. The seed source for KrF excimer MOPA laser system with good optical beam qualit y is obtained.
Third harmonic generation (THG) of Ti:sapphire 744nm laser is produced using two pieces of type Ⅰ BBO crystal while rotating the cardinal plane of the crystal. The relationship between the THG laser energy and the rotate angle is investigated in theory and experiment, the temporal and spatial characters of ω, 2ω, 3ω of output are detected. The seed source for KrF excimer MOPA laser system with good optical beam qualit y is obtained.
1999,
11.
Abstract:
By secondorder and thirdord er p erturbation theory, the interaction rates of intense laser fields at wavelength of 193 nm and 355nm with the conductionband electrons of fused silica are calc ulated. Compared with the linear absorption of the conductionband electron sim ultaneousely absorbing or emitting an acoustic or a longitudinal optical phonon, the linear absorption simultaneousely scattering off a hole and the twophoton absorption are also important in the process of the electrons tr ansferring laser energy to solids.
By secondorder and thirdord er p erturbation theory, the interaction rates of intense laser fields at wavelength of 193 nm and 355nm with the conductionband electrons of fused silica are calc ulated. Compared with the linear absorption of the conductionband electron sim ultaneousely absorbing or emitting an acoustic or a longitudinal optical phonon, the linear absorption simultaneousely scattering off a hole and the twophoton absorption are also important in the process of the electrons tr ansferring laser energy to solids.
1999,
11.
Abstract:
In laser plasma beat wave accelerator，the strong magnetic field higher than 1500 Guass, which can confine the behavior of plasma, is needed .In this paper, the distrib ution of magnetic field on plasma generator is obtained using OPERA3D procedure. The simulation agrees with the experimental data well. While adjusting some parameters，some factors, which cause the actual magnetic f ield lower than the designed one, are found . Based on this simulation, modification has been given．
In laser plasma beat wave accelerator，the strong magnetic field higher than 1500 Guass, which can confine the behavior of plasma, is needed .In this paper, the distrib ution of magnetic field on plasma generator is obtained using OPERA3D procedure. The simulation agrees with the experimental data well. While adjusting some parameters，some factors, which cause the actual magnetic f ield lower than the designed one, are found . Based on this simulation, modification has been given．
1999,
11.
Abstract:
The effect of the transv erse motion on the resolution power and measurement accuracy of the circular ma ss spectrometer is analyzed.Related expressions for determining these effects a re given．
The effect of the transv erse motion on the resolution power and measurement accuracy of the circular ma ss spectrometer is analyzed.Related expressions for determining these effects a re given．
1999,
11.
Abstract:
A series of HfO2/SiO 2 high reflective multilayers whose reflectiv ity are more than 99.5% at wavelength 1064nm are coated by three deposition methods. respectitely, and it is found that the method of the reactive electronic beam evaporation of hafnia got the multilayer samples with the hightest laser induced damage threshold 60J/cm２ for 1064nm, 5ns.
A series of HfO2/SiO 2 high reflective multilayers whose reflectiv ity are more than 99.5% at wavelength 1064nm are coated by three deposition methods. respectitely, and it is found that the method of the reactive electronic beam evaporation of hafnia got the multilayer samples with the hightest laser induced damage threshold 60J/cm２ for 1064nm, 5ns.
1999,
11.
Abstract:
The plasma environment which creates Xray laser brings the difficulty to the application of Xray multilayer reflector .The most difficult is that the Xray emitted by the plasma destroys and damages the multilayer reflector. It is shown by the simulated test that the damage d threshold of Mo/Si multilayer reflector made in china is less than 0.10J/cm 2. With the exposure the radiation dose the roodmean square roughness of multilayer apparently increases and the reflectivity almost drops to zero. Accor ding to these results,the article state some ideas for preventing damages of the multilayer reflector.
The plasma environment which creates Xray laser brings the difficulty to the application of Xray multilayer reflector .The most difficult is that the Xray emitted by the plasma destroys and damages the multilayer reflector. It is shown by the simulated test that the damage d threshold of Mo/Si multilayer reflector made in china is less than 0.10J/cm 2. With the exposure the radiation dose the roodmean square roughness of multilayer apparently increases and the reflectivity almost drops to zero. Accor ding to these results,the article state some ideas for preventing damages of the multilayer reflector.
1999,
11.
Abstract:
The design of attenuation foils for the waveband of Ni like r are earth Xray Laser is described. According to the results of the design, the selfsupport silver and polystyrene(C8H8) attenuation foils are made by magnetron spu ttering and spincoating respectively.The mass thickness of the foils and their thickness homogeneity are measured by an α energy spectrum mass thickness apparatus and an αstep100 thickness measurement a pparatus respectively. The surface impurities of silver attenuation foil are analyzed using Auger Elect ron Spectroscope．
The design of attenuation foils for the waveband of Ni like r are earth Xray Laser is described. According to the results of the design, the selfsupport silver and polystyrene(C8H8) attenuation foils are made by magnetron spu ttering and spincoating respectively.The mass thickness of the foils and their thickness homogeneity are measured by an α energy spectrum mass thickness apparatus and an αstep100 thickness measurement a pparatus respectively. The surface impurities of silver attenuation foil are analyzed using Auger Elect ron Spectroscope．
1999,
11.
Abstract:
Phase distribution of the Binary Optical Element(BOE) with good geometrical structure is obtained by a kind of hybrid algorithm.A continuous phase plate with diameter 100mm is m anufactured by ionetching technique with hollowedout mask on the K9glass substrate. The tolerance of the BOE to the phase distortion with Gauss distribution of the input laser beam and the manufa cturing error are analyzed. The intensity distributi on of the focal spot is measured by a general CCD and a series of attenuators with which the measurement dynamic range is increased. The experimental results after data processing show that the focal s pot with sharp edge, low sidelobes and a certain uniformity is obtained and the center zerothorder pulse is suppressed.
Phase distribution of the Binary Optical Element(BOE) with good geometrical structure is obtained by a kind of hybrid algorithm.A continuous phase plate with diameter 100mm is m anufactured by ionetching technique with hollowedout mask on the K9glass substrate. The tolerance of the BOE to the phase distortion with Gauss distribution of the input laser beam and the manufa cturing error are analyzed. The intensity distributi on of the focal spot is measured by a general CCD and a series of attenuators with which the measurement dynamic range is increased. The experimental results after data processing show that the focal s pot with sharp edge, low sidelobes and a certain uniformity is obtained and the center zerothorder pulse is suppressed.
1999,
11.
Abstract:
The primary theory, the experime ntal methods and results to obtain narrow microwave pulse by gas b reakdown are presented. The basic conclusion is that it is an effective cheap me thod to obtain narrow microwave pulse through gas breakdown, and works well in H PM effect experiment.
The primary theory, the experime ntal methods and results to obtain narrow microwave pulse by gas b reakdown are presented. The basic conclusion is that it is an effective cheap me thod to obtain narrow microwave pulse through gas breakdown, and works well in H PM effect experiment.
1999,
11.
Abstract:
Three types of dielectron ic recombination process for Belike ions Au75+ and Pb78+ are investigated. Based on multiconfiguration HartreeFockRelativistic and distorted wave approaches, total dielectronic recombination rate coefficients are calculated at electron temperature 0.6～10.0keV. Variations of the coefficients with electron temperature,recombination type and atomic number are discussed in detail．
Three types of dielectron ic recombination process for Belike ions Au75+ and Pb78+ are investigated. Based on multiconfiguration HartreeFockRelativistic and distorted wave approaches, total dielectronic recombination rate coefficients are calculated at electron temperature 0.6～10.0keV. Variations of the coefficients with electron temperature,recombination type and atomic number are discussed in detail．
1999,
11.
Abstract:
In the physics design of laser targets, in order to complete spherica limplosion of the capsule located on center of the targets, it is required to create a uniform and clear radiation field. To prevent the heavy element blowoff from the cavity wall into the cavity, an approach making use of getting low Z material filled in the cavity is investigated by analytical method. The sample model provides clear physics pictures. The results show that the approach is a good design.
In the physics design of laser targets, in order to complete spherica limplosion of the capsule located on center of the targets, it is required to create a uniform and clear radiation field. To prevent the heavy element blowoff from the cavity wall into the cavity, an approach making use of getting low Z material filled in the cavity is investigated by analytical method. The sample model provides clear physics pictures. The results show that the approach is a good design.
1999,
11.
Abstract:
2D smallsignal gain of a supersonic COIL by a scanning polyhedron mirrorwas got firstly in out laboratory. The small signal gain along flow directionchanges very slow and drops in the near of upper and lower wall. The boundary lay is thicker wih the distance from the nozzle exit plane and the average thickness is about 4～8mm．
2D smallsignal gain of a supersonic COIL by a scanning polyhedron mirrorwas got firstly in out laboratory. The small signal gain along flow directionchanges very slow and drops in the near of upper and lower wall. The boundary lay is thicker wih the distance from the nozzle exit plane and the average thickness is about 4～8mm．
1999,
11.
Abstract:
The FEL oscillators with highp ower, highefficiency require stable electron beam as a pump. That means e nergy, current and period of ebeam should stabilize pass by pass during a mac ropulse. Actually,it is impossible to keep an absolute stabilization of electron beam during a micropulse. The jitter of ebeam will affect gain of laser seri ously. The effects of energy jitter of ebeam on the gain are studied using the FEL 1D code (W1D) developed by us based on the parameters of the CAEP FIR-FEL. The results show that the energy jitter should be less t han 0.5% for CAEP FIR-FEL.
The FEL oscillators with highp ower, highefficiency require stable electron beam as a pump. That means e nergy, current and period of ebeam should stabilize pass by pass during a mac ropulse. Actually,it is impossible to keep an absolute stabilization of electron beam during a micropulse. The jitter of ebeam will affect gain of laser seri ously. The effects of energy jitter of ebeam on the gain are studied using the FEL 1D code (W1D) developed by us based on the parameters of the CAEP FIR-FEL. The results show that the energy jitter should be less t han 0.5% for CAEP FIR-FEL.
1999,
11.
Abstract:
The mode distributions of unstab le resonators with a phaseunifying output coupler are calculated by Prony met hod, and the relations between mode discrimination, far-field divergence angle and some system parameters are analyzed. The results demonstrate that an output beam with diffraction limit can be obtained at small magnification (M=1.3) by this novel resonator. Compared with conventional unstable resonator,it can be better used to high power chemical oxygeniodine lasers (COIL).
The mode distributions of unstab le resonators with a phaseunifying output coupler are calculated by Prony met hod, and the relations between mode discrimination, far-field divergence angle and some system parameters are analyzed. The results demonstrate that an output beam with diffraction limit can be obtained at small magnification (M=1.3) by this novel resonator. Compared with conventional unstable resonator,it can be better used to high power chemical oxygeniodine lasers (COIL).
1999,
11.
Abstract:
A method to reduce the loss of a holecoupled resonator for a freeele ctron laser oscillator is proposed. A grating with a reflectivity of 50%-70% can be used to cover the hole . Both the extraction and diffraction losses can be reduced effectively, which is confirmed by numericals imulations using a three dimensional code with the parameters of a compact far in frared FEL oscillator built in China Academy of Engineering Physics. Furthermore,it can be used as an electron transparen t mirror to make the FEL device more compact and less expensive．
A method to reduce the loss of a holecoupled resonator for a freeele ctron laser oscillator is proposed. A grating with a reflectivity of 50%-70% can be used to cover the hole . Both the extraction and diffraction losses can be reduced effectively, which is confirmed by numericals imulations using a three dimensional code with the parameters of a compact far in frared FEL oscillator built in China Academy of Engineering Physics. Furthermore,it can be used as an electron transparen t mirror to make the FEL device more compact and less expensive．
1999,
11.
Abstract:
A novel method for measuring the cutoff wavelength of waveguides with arbitrar y complex cross sections is proposed in this paper. Based on the theory of waveguide reson ant cavity, the measurement of complex waveguides is simplified into that of resonant cavities. Consequently, the difficulties of matching and transition are excluded, and high accuracy is also obtained.This measurement method is regarded as a better choice in microwave engineering desig n. The measurement methods for waveguide attenuation and field distribution are also in cluded．
A novel method for measuring the cutoff wavelength of waveguides with arbitrar y complex cross sections is proposed in this paper. Based on the theory of waveguide reson ant cavity, the measurement of complex waveguides is simplified into that of resonant cavities. Consequently, the difficulties of matching and transition are excluded, and high accuracy is also obtained.This measurement method is regarded as a better choice in microwave engineering desig n. The measurement methods for waveguide attenuation and field distribution are also in cluded．
1999,
11.
Abstract:
The influence of annealing and Indium compositions on optical properties of InGaAs quantum dots(QDs) in the GaAs or AlGaAs matrix, grown by molecula r beam epitaxy, has been investigated. It is shown that increasing Indium compos ition in QDs leads to an enhancement of carrier location energy and an increase of the energy gap between ground and excited states in QDs.Vertical couple d QDs with wide band gap AlGaAs matrix will lead to a highert hermal stability. In structures of vertical coupled InGaAs Q Ds in the AlGaAs matrix, high temperature (T=830℃) postgrowth annealing all ows to improve the quality of AlGaAs layers grown at low temperature, while the energy spectra of structures is not significantly changed.
The influence of annealing and Indium compositions on optical properties of InGaAs quantum dots(QDs) in the GaAs or AlGaAs matrix, grown by molecula r beam epitaxy, has been investigated. It is shown that increasing Indium compos ition in QDs leads to an enhancement of carrier location energy and an increase of the energy gap between ground and excited states in QDs.Vertical couple d QDs with wide band gap AlGaAs matrix will lead to a highert hermal stability. In structures of vertical coupled InGaAs Q Ds in the AlGaAs matrix, high temperature (T=830℃) postgrowth annealing all ows to improve the quality of AlGaAs layers grown at low temperature, while the energy spectra of structures is not significantly changed.
1999,
11.
Abstract:
The transporting process of Xray's photons in the spheresymmetric object is simulated with the MonteCarlo method. Ｔhe simulated results of spectra of the output photons on the recording plane are presented,including flux spectra and exposure spectra of the direct p hotons and the scattering ones, in cases of single object and full system. It is shown that the spectrum on the border of object is in analogy to the bremsstrahlung spectrum of the target. The spectra for the region with longer optical length are nearly the same, and so it is with the spectrumaveraged photon energy for the region. This energy is in the regime wh ere the attenuation coefficient of the high Z element is the smallest. It is also shown that, because the quantity loss of photons varies with photon energy, th
The transporting process of Xray's photons in the spheresymmetric object is simulated with the MonteCarlo method. Ｔhe simulated results of spectra of the output photons on the recording plane are presented,including flux spectra and exposure spectra of the direct p hotons and the scattering ones, in cases of single object and full system. It is shown that the spectrum on the border of object is in analogy to the bremsstrahlung spectrum of the target. The spectra for the region with longer optical length are nearly the same, and so it is with the spectrumaveraged photon energy for the region. This energy is in the regime wh ere the attenuation coefficient of the high Z element is the smallest. It is also shown that, because the quantity loss of photons varies with photon energy, th
1999,
11.
Abstract:
The monostable time delay circuit、pulse steeping circuit and antiinterference technique are used in the synchronizer, the synchronous problem of microsecond level pulsed magnetic field and the nanosecond level accelerator is solved, the delay time can be changed in the range of 100μs．
The monostable time delay circuit、pulse steeping circuit and antiinterference technique are used in the synchronizer, the synchronous problem of microsecond level pulsed magnetic field and the nanosecond level accelerator is solved, the delay time can be changed in the range of 100μs．
1999,
11.
Abstract:
The purpose of this paper is to use the FiniteDifference TimeDomain (FDTD) method to study numerically t he resonant effects of FREMP into a cavity through a slot. Computational data i ndicate that FREMP is easier to resonate with a cavity through a slot for the plentiful high frequencies of FREMP. Because of the radiation outward， the a mplitudes of resonant signals attenuate slowly.
The purpose of this paper is to use the FiniteDifference TimeDomain (FDTD) method to study numerically t he resonant effects of FREMP into a cavity through a slot. Computational data i ndicate that FREMP is easier to resonate with a cavity through a slot for the plentiful high frequencies of FREMP. Because of the radiation outward， the a mplitudes of resonant signals attenuate slowly.
1999,
11.
Abstract:
The quantitative relationship between out diameter (O.D.) and thickness of hollow glass microspheres (HGM) made by liquid droplet method is given. The operation conditions, such as distributions of temperature and purge gas velocit y in the furnace, concentrations of solution, and the operation conditions of th e droplet generator, are experimentally optimized, under which HGM is produced with O.D. of 300~450μm, wall thickness of 0.7~1.2μm, aspect ratio of 300~700, surface roughness better than 10nm, concentricity better than 97%, sphericity higher than 99%, and out and inner failure pressures more than 0.91MPa and 0.43MPa respectively.
The quantitative relationship between out diameter (O.D.) and thickness of hollow glass microspheres (HGM) made by liquid droplet method is given. The operation conditions, such as distributions of temperature and purge gas velocit y in the furnace, concentrations of solution, and the operation conditions of th e droplet generator, are experimentally optimized, under which HGM is produced with O.D. of 300~450μm, wall thickness of 0.7~1.2μm, aspect ratio of 300~700, surface roughness better than 10nm, concentricity better than 97%, sphericity higher than 99%, and out and inner failure pressures more than 0.91MPa and 0.43MPa respectively.
1999,
11.
Abstract:
The operative repetition r ate and miniaturization are important to the application of pulse power generato r. This paper presents the high power repetitive pulse generator which consists of Tesla transformer with special magnet core and coaxial pulse forming line. The constru ction,principle and character of the generator are discussed．
The operative repetition r ate and miniaturization are important to the application of pulse power generato r. This paper presents the high power repetitive pulse generator which consists of Tesla transformer with special magnet core and coaxial pulse forming line. The constru ction,principle and character of the generator are discussed．
1999,
11.
Abstract:
The sing periodic cycle pulse of 1.6GW peak power, 20Hz repetition rate has been generated. It radiated peak power of more than 500MW with a coaxial biconical antenna. The insulation properties and energy loss during generating and radiating high peak power and ultrawide band (UWB ) pulse are acquired. The experiments show that the materials insulation and d ispersion in subnanosecond pulse should be further investigated.
The sing periodic cycle pulse of 1.6GW peak power, 20Hz repetition rate has been generated. It radiated peak power of more than 500MW with a coaxial biconical antenna. The insulation properties and energy loss during generating and radiating high peak power and ultrawide band (UWB ) pulse are acquired. The experiments show that the materials insulation and d ispersion in subnanosecond pulse should be further investigated.
