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RSS2004 Vol. 16, No. 06
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2004,
16.
Abstract:
Using the transform-circle graphic method, a new mode-locked laser resonator is analyzed. It is different from general mode-locked Ti: sapphire laser resonator.Using separated laser material and Kerr medium, the resonator can generate fundamental frequency pulse sequences with high energy of 23mJ and double frequency pulse sequences with 13.6mJ.
Using the transform-circle graphic method, a new mode-locked laser resonator is analyzed. It is different from general mode-locked Ti: sapphire laser resonator.Using separated laser material and Kerr medium, the resonator can generate fundamental frequency pulse sequences with high energy of 23mJ and double frequency pulse sequences with 13.6mJ.
2004,
16.
Abstract:
In this paper, the laser thermal effects, produced in the transmitting channel of a beam control system, are numerically analyzed. The laser propagation is governed by the paraxial wave equation, which is solved by the FFT method. The air density variation is calculated with the complete Navier-Stokes equations. The numerical tests are carried out for different wave length of laser and different absorption coefficients of air medium, in order to estimate the effects on the beam quality at far field. The results show that the laser thermal effects in the transmitting channel may largely reduce the concentration of laser energy at far field.
In this paper, the laser thermal effects, produced in the transmitting channel of a beam control system, are numerically analyzed. The laser propagation is governed by the paraxial wave equation, which is solved by the FFT method. The air density variation is calculated with the complete Navier-Stokes equations. The numerical tests are carried out for different wave length of laser and different absorption coefficients of air medium, in order to estimate the effects on the beam quality at far field. The results show that the laser thermal effects in the transmitting channel may largely reduce the concentration of laser energy at far field.
2004,
16.
Abstract:
The product of Fourier series and a finite sum of complex Gaussian functions is used to approximate the window function of a hard-edged aperture, an improved algorithm for the beam propagation through a paraxial ABCD optical system with hard-edged aperture is proposed. The transformation of Gaussian beams is taken as an example, an approximate analytical propagation expression in terms of a sum of elementary functions is derived. Numerical calculation results are given and compared with those by the direct integral of the Collins formula and by using Wen’s method. It is shown that the improved algorithm provides a good trade-off between the computational accuracy and computer time, and is applicable to the far field and near field, whereas there are noticeable discrepancies in the near fi
The product of Fourier series and a finite sum of complex Gaussian functions is used to approximate the window function of a hard-edged aperture, an improved algorithm for the beam propagation through a paraxial ABCD optical system with hard-edged aperture is proposed. The transformation of Gaussian beams is taken as an example, an approximate analytical propagation expression in terms of a sum of elementary functions is derived. Numerical calculation results are given and compared with those by the direct integral of the Collins formula and by using Wen’s method. It is shown that the improved algorithm provides a good trade-off between the computational accuracy and computer time, and is applicable to the far field and near field, whereas there are noticeable discrepancies in the near fi
2004,
16.
Abstract:
Analytical solutions representing the real and imaginary parts of a perturbation field traveling in optical fibers have been derived for the linearized version of the nolinear Ｓhr-dinger equation. These generalized expressions show that the initial variations of the real and imaginary parts of the perturbation are very sensitive to the input conditions.The analytical results show that when z →∞,the gain coefficient of the perturbation approximates to g ,at the initial period the wave number k varies as-z changes, only when-z is sufficient long does the -k approximate to a constant.
Analytical solutions representing the real and imaginary parts of a perturbation field traveling in optical fibers have been derived for the linearized version of the nolinear Ｓhr-dinger equation. These generalized expressions show that the initial variations of the real and imaginary parts of the perturbation are very sensitive to the input conditions.The analytical results show that when z →∞,the gain coefficient of the perturbation approximates to g ,at the initial period the wave number k varies as-z changes, only when-z is sufficient long does the -k approximate to a constant.
2004,
16.
Abstract:
The damage thresholds of Si PIN photodiodes irradiated by 800nm fs laser with pulse duration of 60fs have been measured. The damage thresholds of Si photodiodes irradiated by laser pulse of different duration from 1s to 60fs are present and discussed. Experimental data indicates that damage fluence increases approximately but not strictly with square root of pulse duration for pulses longer than 10ns. The output signal analysis shows the damage was caused mainly by thermal effect. However the damage threshold to 60fs laser is 0.1J/cm2, which deviates apparently from what general temperature distribution model predicted．
The damage thresholds of Si PIN photodiodes irradiated by 800nm fs laser with pulse duration of 60fs have been measured. The damage thresholds of Si photodiodes irradiated by laser pulse of different duration from 1s to 60fs are present and discussed. Experimental data indicates that damage fluence increases approximately but not strictly with square root of pulse duration for pulses longer than 10ns. The output signal analysis shows the damage was caused mainly by thermal effect. However the damage threshold to 60fs laser is 0.1J/cm2, which deviates apparently from what general temperature distribution model predicted．
2004,
16.
Abstract:
The X-ray source based on electron accelerator is the foundation of high energy industrial CT(ICT). A new type of small spot size SW electron linac was designed with high space resolution. This paper discusses that spot size of radial source influence on the imaging quality, and analyzes the physical reason that at high energy the small hole method wasn't suit for the measurement of spot size, it also gives four kinds of measurement method for this type of high energy X-ray source spot size and the analysis of the experiment results. The measurement results show that spot size of the new type accelerator X-ray source is about 1.4mm, and the limited space resolution is 2.5lp/mm.
The X-ray source based on electron accelerator is the foundation of high energy industrial CT(ICT). A new type of small spot size SW electron linac was designed with high space resolution. This paper discusses that spot size of radial source influence on the imaging quality, and analyzes the physical reason that at high energy the small hole method wasn't suit for the measurement of spot size, it also gives four kinds of measurement method for this type of high energy X-ray source spot size and the analysis of the experiment results. The measurement results show that spot size of the new type accelerator X-ray source is about 1.4mm, and the limited space resolution is 2.5lp/mm.
2004,
16.
Abstract:
After expatiating upon the principle of the measurement of spread function of radiography system by method of step, the errors caused by this method are analyzed. The different degrees on measurement caused by different factors (such as the intersectant degree between the axis and the edge of the step, distance between the axis and the step and the width of the step) are compared in detail. The directive principles on experiment set up for measurement of system SF are derived. Something which may be paid attentions to while carrying out the experiment are also pointed out.
After expatiating upon the principle of the measurement of spread function of radiography system by method of step, the errors caused by this method are analyzed. The different degrees on measurement caused by different factors (such as the intersectant degree between the axis and the edge of the step, distance between the axis and the step and the width of the step) are compared in detail. The directive principles on experiment set up for measurement of system SF are derived. Something which may be paid attentions to while carrying out the experiment are also pointed out.
2004,
16.
Abstract:
According to the optimization principle for diodepumped laser, one kind of mini diode-pumped laser for seed-injection is designed. Using the numerical method, the optimized design is presented laser gain media, coupling system and resonant cavity. The seed laser beam from mini diodepumped laser was injected into Q-switched laser and output characteristics of Q-switched laser were studied. The experiment results show that this laser is stable, with high beam quality and small light beam divergence. The lightlight efficiency is 17.4% and slope efficiency is 24%. The output power of this laser is about 80mW. The buildup time of laser pulse in power oscillator decreases by 40ns and the injectedseed laser field improve the distribution of output laser field．
According to the optimization principle for diodepumped laser, one kind of mini diode-pumped laser for seed-injection is designed. Using the numerical method, the optimized design is presented laser gain media, coupling system and resonant cavity. The seed laser beam from mini diodepumped laser was injected into Q-switched laser and output characteristics of Q-switched laser were studied. The experiment results show that this laser is stable, with high beam quality and small light beam divergence. The lightlight efficiency is 17.4% and slope efficiency is 24%. The output power of this laser is about 80mW. The buildup time of laser pulse in power oscillator decreases by 40ns and the injectedseed laser field improve the distribution of output laser field．
2004,
16.
Abstract:
The discharge stability is crucial to the application of a transversely excited atmospheric (TEA) CO2 laser. The dynamic discharge process of a UV-preionized TEA CO2 laser with a charge-discharge-circuit including an inductance was investigated experimentally. The results show that the transit from glow discharge to arc discharge is correlative with the rudimental vibration after the main discharge. Two methods are carried out to avoid the transition to arc discharge: one is to increase the charge inductance, and the other is to replace the charge inductance by a high voltage diode. Both methods can improve the discharge stability and increase the pulse energy effectively.
The discharge stability is crucial to the application of a transversely excited atmospheric (TEA) CO2 laser. The dynamic discharge process of a UV-preionized TEA CO2 laser with a charge-discharge-circuit including an inductance was investigated experimentally. The results show that the transit from glow discharge to arc discharge is correlative with the rudimental vibration after the main discharge. Two methods are carried out to avoid the transition to arc discharge: one is to increase the charge inductance, and the other is to replace the charge inductance by a high voltage diode. Both methods can improve the discharge stability and increase the pulse energy effectively.
2004,
16.
Abstract:
The principle of atmospheric coherence length measurement via differential image motion measure of the optical wave's angle-of-arrival fluctuation is introduced. An instrument for the measurement of atmospheric coherence length both in the daytime and at night were described. The statistical characteristics of the atmospheric coherence length in the daytime and at night were analyzed from some primary observation results. It shows that the refractive index structure constant varies with the time in total layer, and the time-varying behavior is basically in accordance with that of the boundary layer, that is, the atmospheric coherence length during the period of sunrise and sundown is much larger than that in the other periods.
The principle of atmospheric coherence length measurement via differential image motion measure of the optical wave's angle-of-arrival fluctuation is introduced. An instrument for the measurement of atmospheric coherence length both in the daytime and at night were described. The statistical characteristics of the atmospheric coherence length in the daytime and at night were analyzed from some primary observation results. It shows that the refractive index structure constant varies with the time in total layer, and the time-varying behavior is basically in accordance with that of the boundary layer, that is, the atmospheric coherence length during the period of sunrise and sundown is much larger than that in the other periods.
2004,
16.
Abstract:
This paper analyses the diffraction characteristics of grating pair compressor in a CPA(chirped pulse amplification) system, using the 3D raytracing method, under the conditions that the grating grooves are unparallel while the grating surfaces are parallel. In this case, the group delay of optical light passing through this system, the second and the third dispersion of the system and the relative errors of dispersion with the condition that the grating grooves is strictly parallel were calculated. The reception position's variation quantity of the central wavelength light on the reception surface was achieved, meanwhile, its variations with the incident angle varying were analysed.
This paper analyses the diffraction characteristics of grating pair compressor in a CPA(chirped pulse amplification) system, using the 3D raytracing method, under the conditions that the grating grooves are unparallel while the grating surfaces are parallel. In this case, the group delay of optical light passing through this system, the second and the third dispersion of the system and the relative errors of dispersion with the condition that the grating grooves is strictly parallel were calculated. The reception position's variation quantity of the central wavelength light on the reception surface was achieved, meanwhile, its variations with the incident angle varying were analysed.
2004,
16.
Abstract:
Taking the nonlinear refraction and the nonlinear absorption into account simultaneously, this paper investigated the diffraction theory model of the Z-scan technique, and analyzed the features of Z-scan curves and their variation rules. In the case of small nonlinear refraction and absorption the results obtained by this theory are consistent with that of the conventional Z-scan theory. For the materials with the large nonlinear refraction and absorption, the conventional theory become ineffective, but this theory can still give very good results. Numerical results show that the ratio of the nonlinear refraction to absorption is an important parameter that influences the optical power transmitted from the receiving aperture. To acquire a good optical limiting performance, the ratio of the
Taking the nonlinear refraction and the nonlinear absorption into account simultaneously, this paper investigated the diffraction theory model of the Z-scan technique, and analyzed the features of Z-scan curves and their variation rules. In the case of small nonlinear refraction and absorption the results obtained by this theory are consistent with that of the conventional Z-scan theory. For the materials with the large nonlinear refraction and absorption, the conventional theory become ineffective, but this theory can still give very good results. Numerical results show that the ratio of the nonlinear refraction to absorption is an important parameter that influences the optical power transmitted from the receiving aperture. To acquire a good optical limiting performance, the ratio of the
2004,
16.
Abstract:
Based on the introduction on circuit of main pulse and pre-pulse, the scheme about the trigger delay between pre-pulse and main pulse is introduced, and the experimental results about the adjustment of main pulse and pre-pulse are given. After the improvement on the device of capillary discharge soft X-ray laser, the original pre-pulse with over-high current is reduced and a new pre-pulse about tens of amperes is produced by pre-pulse generator. The adjusting results show that the current of pre-pulse is 20A, the first peak current of the main pulse is 40.1kA with 26.6ns risetime and 38ns duration. And the delay time between pre-pulse and main pulse is adjustable from 3μs to 50μs. These parameters can meet the need of soft X-ray laser generation.
Based on the introduction on circuit of main pulse and pre-pulse, the scheme about the trigger delay between pre-pulse and main pulse is introduced, and the experimental results about the adjustment of main pulse and pre-pulse are given. After the improvement on the device of capillary discharge soft X-ray laser, the original pre-pulse with over-high current is reduced and a new pre-pulse about tens of amperes is produced by pre-pulse generator. The adjusting results show that the current of pre-pulse is 20A, the first peak current of the main pulse is 40.1kA with 26.6ns risetime and 38ns duration. And the delay time between pre-pulse and main pulse is adjustable from 3μs to 50μs. These parameters can meet the need of soft X-ray laser generation.
2004,
16.
Abstract:
The 5mm×5mm laser pulse is amplified using 10mm×10mm Nd:YLF laser amplifier tightly ring-pumped by high power LDA and two-stage double-pass abaxial travelling wave amplifying structure. The rules of gain of laser amplifier and amplifying system with pump current and pump delay are studied by simulation and experiment. The two-stage double-pass abaxial small-signal net gain of amplifying system is 600 in experiment, and the energy extract efficiency is 0.86%. The results of experiment and simulation indicate that the structure of the amplifier and amplifying system has high energy extract efficiency and gain, low coupling loss, the advantages of being compact and simple and so on.
The 5mm×5mm laser pulse is amplified using 10mm×10mm Nd:YLF laser amplifier tightly ring-pumped by high power LDA and two-stage double-pass abaxial travelling wave amplifying structure. The rules of gain of laser amplifier and amplifying system with pump current and pump delay are studied by simulation and experiment. The two-stage double-pass abaxial small-signal net gain of amplifying system is 600 in experiment, and the energy extract efficiency is 0.86%. The results of experiment and simulation indicate that the structure of the amplifier and amplifying system has high energy extract efficiency and gain, low coupling loss, the advantages of being compact and simple and so on.
2004,
16.
Abstract:
The evaluating norms of excimer laser beam uniformity are analysed in detail. The process window defines uniformity requirements of the excimer laser,while the energy fraction answers the problem of useful percentage of energy within a giving process window. The top-hat factor defines the uniformity of the whole energy range, and the dynamic range is the variation range of screen-homogeneity in the specific application. The beam uniformity obtained by different beam homogenizer is compared by using CCD laser beam analyzer. With the fly's eye homogenizer, energy untilization ratio is high and the homogeneity of the whole light spot is fine, but the dynamic range of the screen-homogeneity is narrow; The prisms has wide dynamic range but bad homogeneity.
The evaluating norms of excimer laser beam uniformity are analysed in detail. The process window defines uniformity requirements of the excimer laser,while the energy fraction answers the problem of useful percentage of energy within a giving process window. The top-hat factor defines the uniformity of the whole energy range, and the dynamic range is the variation range of screen-homogeneity in the specific application. The beam uniformity obtained by different beam homogenizer is compared by using CCD laser beam analyzer. With the fly's eye homogenizer, energy untilization ratio is high and the homogeneity of the whole light spot is fine, but the dynamic range of the screen-homogeneity is narrow; The prisms has wide dynamic range but bad homogeneity.
2004,
16.
Abstract:
Optical system of Shenguang-Ⅲ works under high power condition and demands that optical elements are highly resistant to laser damage. Micro-defects in optical element may cause enhancement of electric field in small area which will lead to lower laser damage threshold. In this paper, Time-domain finite difference method(FDTD) is used to simulate distribution of electromagnetic field. Quantitative judgement of selection of computation parameters is given. The results show that if micro-defects(such as pore, impurity, etc) exist in the optical material, the intensity of electric field is enhanced by several times.
Optical system of Shenguang-Ⅲ works under high power condition and demands that optical elements are highly resistant to laser damage. Micro-defects in optical element may cause enhancement of electric field in small area which will lead to lower laser damage threshold. In this paper, Time-domain finite difference method(FDTD) is used to simulate distribution of electromagnetic field. Quantitative judgement of selection of computation parameters is given. The results show that if micro-defects(such as pore, impurity, etc) exist in the optical material, the intensity of electric field is enhanced by several times.
2004,
16.
Abstract:
With ferrocene as dopant, Fe-doping PMP foams were prepared by thermalinduced phase inversion. The actual density values of doped foams are higher than the theoretical ones, and increase gradually from top to bottom. At a constant theoretical density, the actual densities of doped foams reduce with Fe content increase. Compared with PMP foam, the size of pore and skeleton of the doped PMP foam is bigger．
With ferrocene as dopant, Fe-doping PMP foams were prepared by thermalinduced phase inversion. The actual density values of doped foams are higher than the theoretical ones, and increase gradually from top to bottom. At a constant theoretical density, the actual densities of doped foams reduce with Fe content increase. Compared with PMP foam, the size of pore and skeleton of the doped PMP foam is bigger．
2004,
16.
Abstract:
In this paper, the effect of smoothing by spectral dispersion (SSD) on the performance of the diffractive optical element (DOE) for beam smoothing is studied. Using SSD technique, the tolerances of the DOE for beam smoothing to wavefront distortion and fabricating error are increased, the high frequency modulation in the intensity distribution is reduced and the performance of beam smoothing is improved. Using SSD and DOE may be consistent with the rigorous demand for beam smoothing in inertial confinement fusion (ICF).
In this paper, the effect of smoothing by spectral dispersion (SSD) on the performance of the diffractive optical element (DOE) for beam smoothing is studied. Using SSD technique, the tolerances of the DOE for beam smoothing to wavefront distortion and fabricating error are increased, the high frequency modulation in the intensity distribution is reduced and the performance of beam smoothing is improved. Using SSD and DOE may be consistent with the rigorous demand for beam smoothing in inertial confinement fusion (ICF).
2004,
16.
Abstract:
Energetic ions generated from a solid target irradiated normally by an ultrashort ultraintense laser pulse is examined by 2D3V particle-in-cell simulations. The energetic ions are observed from both the front and the rear of the target. The ions energy spectra are obtained. The simulation results show that the energetic ions from the front of the target have a rather larger angular distribution, and deposit energy in the target, while the energetic ions from the rear target surface are highly directed and are accelerated to higher energy. The ion energy from the simulation is consistent with that observed in experiments.
Energetic ions generated from a solid target irradiated normally by an ultrashort ultraintense laser pulse is examined by 2D3V particle-in-cell simulations. The energetic ions are observed from both the front and the rear of the target. The ions energy spectra are obtained. The simulation results show that the energetic ions from the front of the target have a rather larger angular distribution, and deposit energy in the target, while the energetic ions from the rear target surface are highly directed and are accelerated to higher energy. The ion energy from the simulation is consistent with that observed in experiments.
2004,
16.
Abstract:
The rotating coil measurement system and the measurement results of quadrupoles for CSRm injection beam line are introduced. The reasons causing the high order harmonic components are analyzed. The short circuit of magnet coils will cause sextupole component and the twists of magnet core will affect the octupole component. Otherwise, the chamfering also makes a great impact on the sextupole and octupole components, and some results are involved too.
The rotating coil measurement system and the measurement results of quadrupoles for CSRm injection beam line are introduced. The reasons causing the high order harmonic components are analyzed. The short circuit of magnet coils will cause sextupole component and the twists of magnet core will affect the octupole component. Otherwise, the chamfering also makes a great impact on the sextupole and octupole components, and some results are involved too.
2004,
16.
Abstract:
This paper studies the space-charge effect of intense current in electrostatic accelerating tube based on 5 hypothese, including the potential distribution in and out beam, the impact on the axial potential by space charge and the transport of intense current. The results show that the radial potential curves of inner beam are all parabolas and they reach the minimum on the axis. The relationship between space-charge fields and the beam radius is linear.The space-charge causes not only the decrease of axial potential, but also the divergency of beam, especially at the low speed of electron. One of the key points lies in the design of the front fields of electrostatic accelerating tube when the space-charge effects are considered, and the fields change of high current tube is greater than t
This paper studies the space-charge effect of intense current in electrostatic accelerating tube based on 5 hypothese, including the potential distribution in and out beam, the impact on the axial potential by space charge and the transport of intense current. The results show that the radial potential curves of inner beam are all parabolas and they reach the minimum on the axis. The relationship between space-charge fields and the beam radius is linear.The space-charge causes not only the decrease of axial potential, but also the divergency of beam, especially at the low speed of electron. One of the key points lies in the design of the front fields of electrostatic accelerating tube when the space-charge effects are considered, and the fields change of high current tube is greater than t
2004,
16.
Abstract:
The paper has established an equivalent-circuit model of the four-level-coaxial-circular-cone-like magnetically insulated transmission line of PBFA Z by treating its vacuum section as several pieces of lumped inductance in terms of its magnetic insulation properties. The model has incorporated magnetic insulation theory, space-charge-limited flow theory, Mendel's MITL pressure balance equation, and wire-array implosion dynamic model as well as several critical geometric parameters of the MITL. The comparison of calculated results of a typical PBFA Z test by the model with those by other models and measured results indicates that the model be valid and can be used as a convenient tool to design and estimate similar MITL configurations.
The paper has established an equivalent-circuit model of the four-level-coaxial-circular-cone-like magnetically insulated transmission line of PBFA Z by treating its vacuum section as several pieces of lumped inductance in terms of its magnetic insulation properties. The model has incorporated magnetic insulation theory, space-charge-limited flow theory, Mendel's MITL pressure balance equation, and wire-array implosion dynamic model as well as several critical geometric parameters of the MITL. The comparison of calculated results of a typical PBFA Z test by the model with those by other models and measured results indicates that the model be valid and can be used as a convenient tool to design and estimate similar MITL configurations.
2004,
16.
Abstract:
Industrial CT adopts electron accelerator to produce the high energy X-ray bremsstrahlung , and makes use of the principle of different absorption coefficient and scattering coefficient when the X-ray cuts through different materials to check the internal blemish or internal structure of the material. The quantity and the speed of creating image of the industrial CT closely relate to the accelerator's focus, the highest X-ray energy, X-rays dose and dose uniformity. Protecting the electronics circuit of the detector against X-ray relate to the detector's service life. The X-rays measuring results given in this article show that the 9MeV LINAC can satisfie the requirements for checking the material structure and blemish by the high energy industrial CT.
Industrial CT adopts electron accelerator to produce the high energy X-ray bremsstrahlung , and makes use of the principle of different absorption coefficient and scattering coefficient when the X-ray cuts through different materials to check the internal blemish or internal structure of the material. The quantity and the speed of creating image of the industrial CT closely relate to the accelerator's focus, the highest X-ray energy, X-rays dose and dose uniformity. Protecting the electronics circuit of the detector against X-ray relate to the detector's service life. The X-rays measuring results given in this article show that the 9MeV LINAC can satisfie the requirements for checking the material structure and blemish by the high energy industrial CT.
2004,
16.
Abstract:
Because of limited sample numbers, imprecise data and dynamic error, statistical method based on probability theory has some shortage in neutrons data processing. Based on Dempster-Shafer (D-S) theory, a method of statistics of neutrons data is described. Appling the basic assign, belief function and plausible function, the lower and upper probability for neutrons randomly distribute to some sets was presented, so was the average neutrons number. The new method of statistics is especially suitable for imprecise data and not restricted by sample numbers．
Because of limited sample numbers, imprecise data and dynamic error, statistical method based on probability theory has some shortage in neutrons data processing. Based on Dempster-Shafer (D-S) theory, a method of statistics of neutrons data is described. Appling the basic assign, belief function and plausible function, the lower and upper probability for neutrons randomly distribute to some sets was presented, so was the average neutrons number. The new method of statistics is especially suitable for imprecise data and not restricted by sample numbers．
2004,
16.
Abstract:
From thermodynamics, the electrode erosion process of high-power gas spark gap switch is analysed in theory. The simplified mathematical model is built and solved numerically, the relations between electrode erosion depth and some characteristics of electrode materials such as density, specific heat, melting point, boiling point, thermal conductivity, and so on, are studied. The capabilities of three common electrodes (made of Cu, W, and Al) to resist erosion are compared, which indicates that a ranking of the erosion rate for three materials, from least to greatest, is W, Cu, Al.
From thermodynamics, the electrode erosion process of high-power gas spark gap switch is analysed in theory. The simplified mathematical model is built and solved numerically, the relations between electrode erosion depth and some characteristics of electrode materials such as density, specific heat, melting point, boiling point, thermal conductivity, and so on, are studied. The capabilities of three common electrodes (made of Cu, W, and Al) to resist erosion are compared, which indicates that a ranking of the erosion rate for three materials, from least to greatest, is W, Cu, Al.
2004,
16.
Abstract:
This paper presents the mechanism of the breakdown of liquids. Experimental apparatus of pulsed breakdown of the pressured deionized water has been set up. The relationship between the pulsed breakdown stress and the water pressure has been investigated. The results of test show that breakdown stress is significantly higher than that one might predict by currently accepted breakdown criteria when a hydrostatic pressure is applied to the water dielectrics. When the pressure of water changed from 0.1MPa to 0.7MPa, breakdown stress of water changed from 25.3MV/m to 46.7MV/m. Using the pressured deionized water as dielectrics, the energy density of the energy system could be enhanced notably and the size of the pulsed power system could be minified too.
This paper presents the mechanism of the breakdown of liquids. Experimental apparatus of pulsed breakdown of the pressured deionized water has been set up. The relationship between the pulsed breakdown stress and the water pressure has been investigated. The results of test show that breakdown stress is significantly higher than that one might predict by currently accepted breakdown criteria when a hydrostatic pressure is applied to the water dielectrics. When the pressure of water changed from 0.1MPa to 0.7MPa, breakdown stress of water changed from 25.3MV/m to 46.7MV/m. Using the pressured deionized water as dielectrics, the energy density of the energy system could be enhanced notably and the size of the pulsed power system could be minified too.
2004,
16.
Abstract:
The paper analytically discusses two factors, the spectrum of photon and the scattered radiation by the detector, which affect the attenuation efficient of the object in flash Xray radiography. The effective attenuation efficient for the object components is evaluated simulating Xphoton transport process in radiographic system using Monte Carlo method. The effective attenuation efficient and its distribution on the image are obtained regardless of scattered effect. The distribution shape is similar to the CT number profile in medical CT reconstruction. The larger the optical path of the photon projecting an image, the smaller the effective attenuation efficient corresponding to the projecting point in the image. It is shown that the average effective attenuation efficient is 0.830cm-1
The paper analytically discusses two factors, the spectrum of photon and the scattered radiation by the detector, which affect the attenuation efficient of the object in flash Xray radiography. The effective attenuation efficient for the object components is evaluated simulating Xphoton transport process in radiographic system using Monte Carlo method. The effective attenuation efficient and its distribution on the image are obtained regardless of scattered effect. The distribution shape is similar to the CT number profile in medical CT reconstruction. The larger the optical path of the photon projecting an image, the smaller the effective attenuation efficient corresponding to the projecting point in the image. It is shown that the average effective attenuation efficient is 0.830cm-1
2004,
16.
Abstract:
An X-band detuned accelerator structure was designed using the Mafia code and the parameters were calculated efficiently through the Lagrange interpolation method, then the characteristics and wakefield of this structure were obtained in the end. The results indicate that this structure not only has high quality factor and high shunt impendence, but also can suppress the wakefield to decrease significantly to a low level comparing with the constant impedance accelerator structure, so that the probability of beam break-up is reduced to a great extent.
An X-band detuned accelerator structure was designed using the Mafia code and the parameters were calculated efficiently through the Lagrange interpolation method, then the characteristics and wakefield of this structure were obtained in the end. The results indicate that this structure not only has high quality factor and high shunt impendence, but also can suppress the wakefield to decrease significantly to a low level comparing with the constant impedance accelerator structure, so that the probability of beam break-up is reduced to a great extent.
2004,
16.
Abstract:
The structure optimization of 142.8MHz subharmonic buncher has been carried out with two-dimensional Finite Ｄifference Ｍethod software Superfish and threedimensional Finite Integration Method software MAFIA. The method of optimizing the cavity structure is presented in this paper, and the optimized structure of the cavity is also decided. The simulation results of Superfish and MAFIA are analyzed and compared, and they are consistent with the design data. In addition, the application of methods of Superfish and MAFIA in the cavity design are also investigated.
The structure optimization of 142.8MHz subharmonic buncher has been carried out with two-dimensional Finite Ｄifference Ｍethod software Superfish and threedimensional Finite Integration Method software MAFIA. The method of optimizing the cavity structure is presented in this paper, and the optimized structure of the cavity is also decided. The simulation results of Superfish and MAFIA are analyzed and compared, and they are consistent with the design data. In addition, the application of methods of Superfish and MAFIA in the cavity design are also investigated.
2004,
16.
Abstract:
Particular simulations on the 34GHz Gyrotrons magnetic injection gun(MIG) consider the influences of such design parameters as: control anode voltage, beam current, structure of MIG and external dc magnetic field. The results show that when control anode voltage increases or magnetic induction intension near cathode decreases, beam velocity ratio will increase while beam velocity spread decreases; as known, beam motion in the gun is affected by the interaction of magnetic field and space charge force, when beam current changes, the minimal velocity spread will gain at a best current; when the magnetic field compression ratio changes lower, the best current value will raise, and beam velocity ratio decrease, meanwhile minimal velocity spread will be a new higher value. The structure of the
Particular simulations on the 34GHz Gyrotrons magnetic injection gun(MIG) consider the influences of such design parameters as: control anode voltage, beam current, structure of MIG and external dc magnetic field. The results show that when control anode voltage increases or magnetic induction intension near cathode decreases, beam velocity ratio will increase while beam velocity spread decreases; as known, beam motion in the gun is affected by the interaction of magnetic field and space charge force, when beam current changes, the minimal velocity spread will gain at a best current; when the magnetic field compression ratio changes lower, the best current value will raise, and beam velocity ratio decrease, meanwhile minimal velocity spread will be a new higher value. The structure of the
2004,
16.
Abstract:
This paper presents the design and initial operation of a double anode magnetron injection gun (MIG) for a 34GHz basic wave gyro-klystron. To accurately determine the beam characteristics of MIG, a theory model with cathode emission is built. A new computer program is employed to simulate electron and cathode emission. Simulation and measurement results indicate that magnetic field influences the beam current of MIG, and the beam current of the MIG depends on the cathode temperature and space charge effect．
This paper presents the design and initial operation of a double anode magnetron injection gun (MIG) for a 34GHz basic wave gyro-klystron. To accurately determine the beam characteristics of MIG, a theory model with cathode emission is built. A new computer program is employed to simulate electron and cathode emission. Simulation and measurement results indicate that magnetic field influences the beam current of MIG, and the beam current of the MIG depends on the cathode temperature and space charge effect．
2004,
16.
Abstract:
A compact L-band magnetically insulated transmission line oscillator (MILO) is configured and fabricated．When the input voltage is 515～538kV, and the diode current is 58～61kA, high power microwaves of the TM01 mode are generated from the device with the frequency of 176～178GHz，output power of 22～25GW， and the power conversion efficiency of 73%~79%in experiments. The experimental results agree well with that of simulation.
A compact L-band magnetically insulated transmission line oscillator (MILO) is configured and fabricated．When the input voltage is 515～538kV, and the diode current is 58～61kA, high power microwaves of the TM01 mode are generated from the device with the frequency of 176～178GHz，output power of 22～25GW， and the power conversion efficiency of 73%~79%in experiments. The experimental results agree well with that of simulation.
