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RSS2004 Vol. 16, No. 12
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2004,
16.
Abstract:
Computer tomography is widely used in density measurement, and this method is also introduced into analysis of airflow as optical tomography. The airflow characteristic of thermal blooming in high energy laser(HEL) beam and the disadvantage of traditional method are discussed. The optical tomography of thermal blooming is presented in this paper, and it can measure HEL inner beam thermal blooming nonintrusively. By the numerical simulation of tomographic optical HEL beam thermal blooming, the feasibility and dependability of this approach are tested.
Computer tomography is widely used in density measurement, and this method is also introduced into analysis of airflow as optical tomography. The airflow characteristic of thermal blooming in high energy laser(HEL) beam and the disadvantage of traditional method are discussed. The optical tomography of thermal blooming is presented in this paper, and it can measure HEL inner beam thermal blooming nonintrusively. By the numerical simulation of tomographic optical HEL beam thermal blooming, the feasibility and dependability of this approach are tested.
2004,
16.
Abstract:
A new method of faint-target detection is put forward. To improve the practicality of the method, especially it is used to deal with those images that involves the complex background and a lot of noise, the method of neighborhood entropy was brought forward. Furthermore, to increase the validity of it, this method was combined with gray morphological filtering. First ,the image is processed with morphological filtering. Second, the neigborhood entropy is calculated. And then, the target is detected according to the maximum value and minimum value of entropy. The experiment results indicated the new method can detect small target stably and guickly.
A new method of faint-target detection is put forward. To improve the practicality of the method, especially it is used to deal with those images that involves the complex background and a lot of noise, the method of neighborhood entropy was brought forward. Furthermore, to increase the validity of it, this method was combined with gray morphological filtering. First ,the image is processed with morphological filtering. Second, the neigborhood entropy is calculated. And then, the target is detected according to the maximum value and minimum value of entropy. The experiment results indicated the new method can detect small target stably and guickly.
2004,
16.
Abstract:
Numerical analysis of a Yb3+-doped fiber laser pumped by 980nm laser source has been presented in this paper. It has been studied that the relationships between the important characteristics of the Yb3+ doped fiber laser such as threshold power, output power and gain and laser parameters such as pump power, fiber length, mirror reflectivity and Yb3+ concentration. A highly-doped Yb3+ fiber ring laser with short cavity has been presented. Numerical results are coincident with the experiment phenomenon.
Numerical analysis of a Yb3+-doped fiber laser pumped by 980nm laser source has been presented in this paper. It has been studied that the relationships between the important characteristics of the Yb3+ doped fiber laser such as threshold power, output power and gain and laser parameters such as pump power, fiber length, mirror reflectivity and Yb3+ concentration. A highly-doped Yb3+ fiber ring laser with short cavity has been presented. Numerical results are coincident with the experiment phenomenon.
2004,
16.
Abstract:
The influence of penetration depth of iodine flow on COIL output power was experimentally investigated on a COIL with a 250mmol/s (Cl2 flowrate) pipe-array jet-type singlet oxygen generator. The experimental results showed that penetration depth strongly influences COIL output power, and there is an optimal penetration depth, which agrees well with theoretical calculations.
The influence of penetration depth of iodine flow on COIL output power was experimentally investigated on a COIL with a 250mmol/s (Cl2 flowrate) pipe-array jet-type singlet oxygen generator. The experimental results showed that penetration depth strongly influences COIL output power, and there is an optimal penetration depth, which agrees well with theoretical calculations.
2004,
16.
Abstract:
The X-ray transmission property of mono-capillaries is the basis for designing X-ray lens. Based on the theory of X-ray transmission through capillaries, a detailed Monte-Carlo method is suggested in this paper. A corresponding computer program is worked out. For a given model, the transmission efficiencies of mono-capillaries versus diameter, incident focus and curvature radius are calculated. The transmission efficiencies of straight capillary reduce as capillary diameter increases. The transmission efficiencies of curved capillary increase as capillary curvature increase. The simulative results agree well with the corresponding experimental results．
The X-ray transmission property of mono-capillaries is the basis for designing X-ray lens. Based on the theory of X-ray transmission through capillaries, a detailed Monte-Carlo method is suggested in this paper. A corresponding computer program is worked out. For a given model, the transmission efficiencies of mono-capillaries versus diameter, incident focus and curvature radius are calculated. The transmission efficiencies of straight capillary reduce as capillary diameter increases. The transmission efficiencies of curved capillary increase as capillary curvature increase. The simulative results agree well with the corresponding experimental results．
2004,
16.
Abstract:
Ｕsing the surface thermal lensing technique, weak absorption of different optical thin films, including the single-layer ZnS and YbF3 dielectric thin films with different thickness, as well as the different multilayer thin films YbF3/ZnS deposited on Si, and multilayer antireflectivity thin films YbF3/ZnS deposited on CaF2 window has been measured. The experimental results of films irradiated by 3.8μm and 2.8μm lasers have been compared and analyzed. The experimental results show that absorption at 2.8μm, is much greater than the one at 3.8μm,and the difference between them is one order of magnitude. The lowest absorption at 3.8μm is 4.57×10－4, and the system sensitivity is 10－５ level．
Ｕsing the surface thermal lensing technique, weak absorption of different optical thin films, including the single-layer ZnS and YbF3 dielectric thin films with different thickness, as well as the different multilayer thin films YbF3/ZnS deposited on Si, and multilayer antireflectivity thin films YbF3/ZnS deposited on CaF2 window has been measured. The experimental results of films irradiated by 3.8μm and 2.8μm lasers have been compared and analyzed. The experimental results show that absorption at 2.8μm, is much greater than the one at 3.8μm,and the difference between them is one order of magnitude. The lowest absorption at 3.8μm is 4.57×10－4, and the system sensitivity is 10－５ level．
2004,
16.
Abstract:
The irradiating style of laser relative to the flying cylinder has to be considered whether the laser is from land or air. With specific assumptions, the analytical expressions of heating power area density distribution on the side of the cylinder is deduced. According to an ideal scenario, analytical deduction is carried out on the incidence angle factor, the excursion of the light spot center and the deformation of the light spot shape. The analysis shows that even if the cylinder does not spin, the light intensity center would wander on the side of the cylinder and the light intensity distribution would vary, especially that along the axial direction would vary greater. It requires detail study on the procedure combined with reality later.
The irradiating style of laser relative to the flying cylinder has to be considered whether the laser is from land or air. With specific assumptions, the analytical expressions of heating power area density distribution on the side of the cylinder is deduced. According to an ideal scenario, analytical deduction is carried out on the incidence angle factor, the excursion of the light spot center and the deformation of the light spot shape. The analysis shows that even if the cylinder does not spin, the light intensity center would wander on the side of the cylinder and the light intensity distribution would vary, especially that along the axial direction would vary greater. It requires detail study on the procedure combined with reality later.
2004,
16.
Abstract:
The effect of the phase-change cooling mirror will depend on the fabrication. Compared to the different computing result through finite element method, the radialized shape is chosen to be the optimum design. For Si mirror, with 80mm in diameter and 12.5mm in depth, the optimum channel fabrication has the depth of 9.9mm and width of 0.4mm and the smallest thermal deformation is 0.37μm after 10s irradiation by a coaxial light whose diameter is 40mm and net absorbing power density is 79-58kW/m2．
The effect of the phase-change cooling mirror will depend on the fabrication. Compared to the different computing result through finite element method, the radialized shape is chosen to be the optimum design. For Si mirror, with 80mm in diameter and 12.5mm in depth, the optimum channel fabrication has the depth of 9.9mm and width of 0.4mm and the smallest thermal deformation is 0.37μm after 10s irradiation by a coaxial light whose diameter is 40mm and net absorbing power density is 79-58kW/m2．
2004,
16.
Abstract:
An analytic solution of Yb-doped double-clad fiber lasers(DCFL) is presented, and some typical parameters which may influence the slope efficiency of DCFL are discussed based on this analytic solution, such as the reflection of pump power and the signal's scatter loss. It is found that the slope efficiency doesn't always increase with the augment of the reflection of pump power. The change of the reflection will affect the optimal length of the fiber. So it is important to balance between the reflection of pump power and the signal loss. Higher concentration of Yb and lower signal loss will also obviously improve the slope efficiency.
An analytic solution of Yb-doped double-clad fiber lasers(DCFL) is presented, and some typical parameters which may influence the slope efficiency of DCFL are discussed based on this analytic solution, such as the reflection of pump power and the signal's scatter loss. It is found that the slope efficiency doesn't always increase with the augment of the reflection of pump power. The change of the reflection will affect the optimal length of the fiber. So it is important to balance between the reflection of pump power and the signal loss. Higher concentration of Yb and lower signal loss will also obviously improve the slope efficiency.
2004,
16.
Abstract:
Designs of targets used in the current Rayleigh-Taylor instability experiments are analyzed and summarized in this paper. The preparation of the perturbation target is developing from two-dimensional to three-dimensional. New designs such as spheric and cylindrical target appeared. Preparation techniques include micromachining, laser, electron and iron beam etching, semiconductor technology, and nano-technology. Laser two-beam interference and electric plating technique for planar target fabrication is studied. According to the novel foreign designs as well as domestic conditions and need, possible designs for recent use such as rapid prototyping and EDM technique for cylindrical target and laser machining technique for spheric target fabrication are proposed.
Designs of targets used in the current Rayleigh-Taylor instability experiments are analyzed and summarized in this paper. The preparation of the perturbation target is developing from two-dimensional to three-dimensional. New designs such as spheric and cylindrical target appeared. Preparation techniques include micromachining, laser, electron and iron beam etching, semiconductor technology, and nano-technology. Laser two-beam interference and electric plating technique for planar target fabrication is studied. According to the novel foreign designs as well as domestic conditions and need, possible designs for recent use such as rapid prototyping and EDM technique for cylindrical target and laser machining technique for spheric target fabrication are proposed.
2004,
16.
Abstract:
Based on the closed-form propagation expression of Hermite-coshGaussian beams passing through an unapertured thin lens, intensity distributions in focal region were studied. Focal shifts of the beams and dependences of maximal intensity position on decentered parameter were investigated. The results show that the relative focal shifts (absolute value) in TEM11mode HermitecoshGaussian beams increase with decreasing decentered parameter and Fresnel number, and tend zero with large Fresnel number. For TEM22mode Hermite-cosh-Gaussian beams the principal maximum intensity is located off the axis when the decentered parameter is smaller than 0.54 and on the axis when decentered parameter is greater than 0.54. When decentered parameter equals 0.54, the beam has double principal maximum
Based on the closed-form propagation expression of Hermite-coshGaussian beams passing through an unapertured thin lens, intensity distributions in focal region were studied. Focal shifts of the beams and dependences of maximal intensity position on decentered parameter were investigated. The results show that the relative focal shifts (absolute value) in TEM11mode HermitecoshGaussian beams increase with decreasing decentered parameter and Fresnel number, and tend zero with large Fresnel number. For TEM22mode Hermite-cosh-Gaussian beams the principal maximum intensity is located off the axis when the decentered parameter is smaller than 0.54 and on the axis when decentered parameter is greater than 0.54. When decentered parameter equals 0.54, the beam has double principal maximum
2004,
16.
Abstract:
laser system with high output stability was designed for three-stage optical parametric chirped-pulse amplification(OPCPA). The PPKTP crystal was chosed as the first-stage gain medium, the LBO and the KDP crystal were used for the second-stage and third-stage, respectively. Through numerical simulations, the output gain and gain stability were obtained for three stage optical parametric chirped pulse saturated amplification. In the case of pumping intensity jitter less than 6%, the output gain jitter of the OPCPA system is less than 1%. In the case of PPKTP crystal chosed as the first-stage quasi-phase matching gain medium, with a pump peak intensity of 30MW/cm2, which is far from damaging the PPKTP crystal, the saturation amplificated gain is 2×105 and the conversion efficiency is 20%.
laser system with high output stability was designed for three-stage optical parametric chirped-pulse amplification(OPCPA). The PPKTP crystal was chosed as the first-stage gain medium, the LBO and the KDP crystal were used for the second-stage and third-stage, respectively. Through numerical simulations, the output gain and gain stability were obtained for three stage optical parametric chirped pulse saturated amplification. In the case of pumping intensity jitter less than 6%, the output gain jitter of the OPCPA system is less than 1%. In the case of PPKTP crystal chosed as the first-stage quasi-phase matching gain medium, with a pump peak intensity of 30MW/cm2, which is far from damaging the PPKTP crystal, the saturation amplificated gain is 2×105 and the conversion efficiency is 20%.
2004,
16.
Abstract:
In order to study the influence by pre-pulse discharge on capillary discharge pumped X-ray Laser, in this paper, a simplified XDCH code is used to simulate the process of pre-discharge with 2μs pulse width in polythene capillary filled with Ar. The plasma temperature, density and ionization degree calculated as initial condition are inputted into XDCH code to simulate typical main-discharge with 40kA. From the view of 1-dimension, some gain coefficient and electron density distributions with typical pre-pulse amplitudes are given. After analysis and comparison, conclusion is drawn that 100A pre-pulse with 2μs width can lead to higher gain. Two-peak structure in time spectrum and ring-like structure in space spectrum of 46.9nm laser line are predicted.
In order to study the influence by pre-pulse discharge on capillary discharge pumped X-ray Laser, in this paper, a simplified XDCH code is used to simulate the process of pre-discharge with 2μs pulse width in polythene capillary filled with Ar. The plasma temperature, density and ionization degree calculated as initial condition are inputted into XDCH code to simulate typical main-discharge with 40kA. From the view of 1-dimension, some gain coefficient and electron density distributions with typical pre-pulse amplitudes are given. After analysis and comparison, conclusion is drawn that 100A pre-pulse with 2μs width can lead to higher gain. Two-peak structure in time spectrum and ring-like structure in space spectrum of 46.9nm laser line are predicted.
2004,
16.
Abstract:
The X-ray radiography technique was used to measure ICF targets and record film images of microspheres using contact microradiography. Then the film images were set under the microscope and converted to digital images by a CCD camera. Based on the information of these digital images,a computer algorithm has been developed for calculating the target shell parameters. This accepted procedure first locates the center of the microsphere using radial averaging of X-ray images, then calculate the radial second derivative of X-ray transmission intensity through a shell to locate the points of inflection in the transimssion intensity vs radius plot which denote the layer interfaces with the accuracy of about 0.2pixels．
The X-ray radiography technique was used to measure ICF targets and record film images of microspheres using contact microradiography. Then the film images were set under the microscope and converted to digital images by a CCD camera. Based on the information of these digital images,a computer algorithm has been developed for calculating the target shell parameters. This accepted procedure first locates the center of the microsphere using radial averaging of X-ray images, then calculate the radial second derivative of X-ray transmission intensity through a shell to locate the points of inflection in the transimssion intensity vs radius plot which denote the layer interfaces with the accuracy of about 0.2pixels．
2004,
16.
Abstract:
The detection system consists of filter,XRD,SUJ-50-10 cable and different band oscillograph. 20TW laser facility of Shanghai Laser Unite Laboratory with energy about 20J,pulse width about 1ps was used, and Au foil target irradiated by laser pulse produced X-ray emission. Note oscillograph type have TK684C,TK694C and WM8500. The linear fit and comparision analysis of experiment data are proceeded. The response time of a filterXRD detection system become fast along with based voltage, and become solw along with cable lenght. Therefor, when fast signal is measured, based voltage of detector must be inreased, and cable length be shorten, and high band oscillograph be selected, in order to reduce system response time and decrease signal distortion．
The detection system consists of filter,XRD,SUJ-50-10 cable and different band oscillograph. 20TW laser facility of Shanghai Laser Unite Laboratory with energy about 20J,pulse width about 1ps was used, and Au foil target irradiated by laser pulse produced X-ray emission. Note oscillograph type have TK684C,TK694C and WM8500. The linear fit and comparision analysis of experiment data are proceeded. The response time of a filterXRD detection system become fast along with based voltage, and become solw along with cable lenght. Therefor, when fast signal is measured, based voltage of detector must be inreased, and cable length be shorten, and high band oscillograph be selected, in order to reduce system response time and decrease signal distortion．
2004,
16.
Abstract:
This paper presents a theoretical analysis model based on the parapotential flow and “fourphase” charge flow models.The model could more exactly describe the physics process in a low-impedance MA intense pinched beam diode. In the model, the evolution of electrons is divided into three phases:no pinching phase, weak pinch phase and tight pinch phase,and in each phase a proper empirical formula is provided for writing the characters of electron beam. Using the KARAT PIC program, the evolution process of electron flow was simulated in the diode, which was designed to test on the Qiangguang-I accelerator for producing intensive current pinched electron beam. Moreover, the experiment with the diode was carried out on QiangguangI accelerator. The contrast between simulated and experimenta
This paper presents a theoretical analysis model based on the parapotential flow and “fourphase” charge flow models.The model could more exactly describe the physics process in a low-impedance MA intense pinched beam diode. In the model, the evolution of electrons is divided into three phases:no pinching phase, weak pinch phase and tight pinch phase,and in each phase a proper empirical formula is provided for writing the characters of electron beam. Using the KARAT PIC program, the evolution process of electron flow was simulated in the diode, which was designed to test on the Qiangguang-I accelerator for producing intensive current pinched electron beam. Moreover, the experiment with the diode was carried out on QiangguangI accelerator. The contrast between simulated and experimenta
2004,
16.
Abstract:
This article presents experimental results of the trigger characteristics of fast-pulse-triggered polymer-foil switch. The results show that the ratio of working voltage to self-greakdown voltage, the trigger voltage, the polarity and the distances between electrodes influence the switch’s performance significantly. The risetime of output pulse is smaller than 2ns that includes the risetime of measure system, the delay is 1~2ns and the jitter is sub-nanosecond. The delay and jitter decrease with raising the trigger voltage and the ratio of working voltage to self-breakdown voltage, and increase with enlarging the distances between main electrodes and trigger electrode. Among the four polarity combinations, the delay and the jitter are minimum for ‘p-n’, follow in sequence for ‘n-p’ an
This article presents experimental results of the trigger characteristics of fast-pulse-triggered polymer-foil switch. The results show that the ratio of working voltage to self-greakdown voltage, the trigger voltage, the polarity and the distances between electrodes influence the switch’s performance significantly. The risetime of output pulse is smaller than 2ns that includes the risetime of measure system, the delay is 1~2ns and the jitter is sub-nanosecond. The delay and jitter decrease with raising the trigger voltage and the ratio of working voltage to self-breakdown voltage, and increase with enlarging the distances between main electrodes and trigger electrode. Among the four polarity combinations, the delay and the jitter are minimum for ‘p-n’, follow in sequence for ‘n-p’ an
2004,
16.
Abstract:
In this paper, the multiple scattering effects of residual gas as isotropic disturbing forces, are introduced into the RMS envelope equation of cylindrically symmetric DC electron beams, so that the expression of emittance growth due to the scattering is obtained. Referring to the design parameters of beam transport system of DragonI LIA, the emittance growth is calculated. The result shows that the emittance growth due to gas scattering could be neglected if the pressure of vacuum tube is less than 3×１０－４Pa. And the measures to restrain the scattering effects are discussed．
In this paper, the multiple scattering effects of residual gas as isotropic disturbing forces, are introduced into the RMS envelope equation of cylindrically symmetric DC electron beams, so that the expression of emittance growth due to the scattering is obtained. Referring to the design parameters of beam transport system of DragonI LIA, the emittance growth is calculated. The result shows that the emittance growth due to gas scattering could be neglected if the pressure of vacuum tube is less than 3×１０－４Pa. And the measures to restrain the scattering effects are discussed．
2004,
16.
Abstract:
The configuration and simulation model of water pulse forming line switch with prepulse suppression ground plane (PPS) were introduced in this paper. The influence of the PPS was analyzed using Pspice. As well as the capacitances between the electrodes or input/output line and PPS(Cpi and Cpo), the inductance(Lp) and capacitance(Cp) of the gaps suppresses the prepulse. The simulation results indicate that the influence of the latter is small. The wave-shapes of the experiment on Flash-Ⅱ accelerator are compared with that of simulation. It suggests that the equivalent circuit model is feasible in water switch design. Cpi and Cpo of the switch must make certain by adjusting the position of PPS firstly, Lp and Cp of the switch should be as small as possible, and the size of holes on PPS must
The configuration and simulation model of water pulse forming line switch with prepulse suppression ground plane (PPS) were introduced in this paper. The influence of the PPS was analyzed using Pspice. As well as the capacitances between the electrodes or input/output line and PPS(Cpi and Cpo), the inductance(Lp) and capacitance(Cp) of the gaps suppresses the prepulse. The simulation results indicate that the influence of the latter is small. The wave-shapes of the experiment on Flash-Ⅱ accelerator are compared with that of simulation. It suggests that the equivalent circuit model is feasible in water switch design. Cpi and Cpo of the switch must make certain by adjusting the position of PPS firstly, Lp and Cp of the switch should be as small as possible, and the size of holes on PPS must
2004,
16.
Abstract:
The process of bearing balls in the plasma immersion ion implantation(PIII) was simulated using a 2-dimensional particle-in-cell (PIC) model. The distributions of normalized potential and dose were studied. In order to avoid overlap of sheaths between different balls in batch process, the minimum distance between two neighboring balls was calculated. When the voltage is -40 kV, plasma density is 4.8×109cm-3 and pulse width is 10μs, the minimum distance between two balls should be 34.18 cm. In addition, the dose distribution along the circumference of the ball is non-uniform. Consequently, a revolving substrate was used to improve the uniformity. Furthermore, to evaluate the model, the expansion process of sheath was measured using a Langmuir probe. Experimental results agree with the cal
The process of bearing balls in the plasma immersion ion implantation(PIII) was simulated using a 2-dimensional particle-in-cell (PIC) model. The distributions of normalized potential and dose were studied. In order to avoid overlap of sheaths between different balls in batch process, the minimum distance between two neighboring balls was calculated. When the voltage is -40 kV, plasma density is 4.8×109cm-3 and pulse width is 10μs, the minimum distance between two balls should be 34.18 cm. In addition, the dose distribution along the circumference of the ball is non-uniform. Consequently, a revolving substrate was used to improve the uniformity. Furthermore, to evaluate the model, the expansion process of sheath was measured using a Langmuir probe. Experimental results agree with the cal
2004,
16.
Abstract:
Being a novel functional material, the ferroelectric cathode materials were studied well with the leaded materials for their high electron emission density. In this paper, the initial experiment of electron emission was carried out with the lead-free ferroelectric ceramics Na1/2 Bi1/2Ti O3 -BaTiO3 (BNBT). High current density about 20A/cm2 has been obtained with the excitation voltage around 11kV. In contrast with the lead zirconate titanate (PZT), BNBT's emission current density is lower but its parameter stability is better. The initial data show that BNBT is a potential lead-free ferroelectric cathode material.
Being a novel functional material, the ferroelectric cathode materials were studied well with the leaded materials for their high electron emission density. In this paper, the initial experiment of electron emission was carried out with the lead-free ferroelectric ceramics Na1/2 Bi1/2Ti O3 -BaTiO3 (BNBT). High current density about 20A/cm2 has been obtained with the excitation voltage around 11kV. In contrast with the lead zirconate titanate (PZT), BNBT's emission current density is lower but its parameter stability is better. The initial data show that BNBT is a potential lead-free ferroelectric cathode material.
2004,
16.
Abstract:
Principle of flash X-ray radiography was introduced and relative mass absorption coefficient were put forward for flash radiography.Based on mono-energy model,the radiographic image was determined by path-length of object only, so the relative mass absorption coefficient could be measured from the image's optic density versus path-length curve. The relative mass absorption coefficient of tungsten was measured from the images of two triangular prism made of tungsten and Fe respectively,which is 1.23, very close to the simulating result 1.26．
Principle of flash X-ray radiography was introduced and relative mass absorption coefficient were put forward for flash radiography.Based on mono-energy model,the radiographic image was determined by path-length of object only, so the relative mass absorption coefficient could be measured from the image's optic density versus path-length curve. The relative mass absorption coefficient of tungsten was measured from the images of two triangular prism made of tungsten and Fe respectively,which is 1.23, very close to the simulating result 1.26．
2004,
16.
Abstract:
This paper firstly derives expressions of current and voltage at various work modes for the series resonant charging power supply, gives recursion formulas calculating the value of current and voltage at various periods; secondly, utilizing recursion formulas, it makes out that the power supply characterizes pulse constant current charging; thirdly, this paper calculates the parameters of the power supply when capacitor-load incompletely discharge, the power supply provides half the maximum output when capacitor-load completely discharge, and provides maximum output to maintain the voltage of capacitor-load; at last, describes a 100Hz steady operation power supply for accelerator utilizing Tesla transformer, measured results and calculated results are well consistent．
This paper firstly derives expressions of current and voltage at various work modes for the series resonant charging power supply, gives recursion formulas calculating the value of current and voltage at various periods; secondly, utilizing recursion formulas, it makes out that the power supply characterizes pulse constant current charging; thirdly, this paper calculates the parameters of the power supply when capacitor-load incompletely discharge, the power supply provides half the maximum output when capacitor-load completely discharge, and provides maximum output to maintain the voltage of capacitor-load; at last, describes a 100Hz steady operation power supply for accelerator utilizing Tesla transformer, measured results and calculated results are well consistent．
2004,
16.
Abstract:
A switch with three groups of electrodes was developed. The feasibility of the concomitance of multi-group electrodes, the switch structure and the internal electric field were analyzed. The current through the switch was calculated using the software Pspice. When a couple of electrodes of this switch are in operation, the voltage is about 50kV, the current is above 100kA, and the pulse width is around 20μs. When three triggered pulses of 1ms interval are fed in three trigger poles of the switch respectively, the switch can produce three 1ms interval pulses through the inductance load, each has the voltage of 38kV, current of about 100kA and width of about 20μs.
A switch with three groups of electrodes was developed. The feasibility of the concomitance of multi-group electrodes, the switch structure and the internal electric field were analyzed. The current through the switch was calculated using the software Pspice. When a couple of electrodes of this switch are in operation, the voltage is about 50kV, the current is above 100kA, and the pulse width is around 20μs. When three triggered pulses of 1ms interval are fed in three trigger poles of the switch respectively, the switch can produce three 1ms interval pulses through the inductance load, each has the voltage of 38kV, current of about 100kA and width of about 20μs.
2004,
16.
Abstract:
Using the water and ethylene glycol mixtures with volume fraction of 36.5%,48.7%,59.0% and 71.2% as the dielectric of the coaxial transmission line, experimental research on the breakdown of mixtures when the inner conductor was charged negative voltage in microseconds was conducted. the breakdown strength,breakdown time,relative permittivity and resistivity of the mixtures as a function of volume fraction was studied. Compared the mixture of 71.2% to the mixture of 36.5%, the results show that the breakdown strength increased 25.1% and the breakdown time delayed 10.49%,but the relative permittivity decreased 7.91%. Furthermore, the breakdown strength of mixtures increased with the decrease of the charge time.
Using the water and ethylene glycol mixtures with volume fraction of 36.5%,48.7%,59.0% and 71.2% as the dielectric of the coaxial transmission line, experimental research on the breakdown of mixtures when the inner conductor was charged negative voltage in microseconds was conducted. the breakdown strength,breakdown time,relative permittivity and resistivity of the mixtures as a function of volume fraction was studied. Compared the mixture of 71.2% to the mixture of 36.5%, the results show that the breakdown strength increased 25.1% and the breakdown time delayed 10.49%,but the relative permittivity decreased 7.91%. Furthermore, the breakdown strength of mixtures increased with the decrease of the charge time.
2004,
16.
Abstract:
Magnetic field affects strongly characteristics of spherical cathode diode. The numerical research shows that the effect of magnetic field (include self-magnetic field and external magnetic field) on diode takes place via varying the tracks of electron beam. The space charge limited current decreases as external applied magnetic field increases. With intense enough external applied magnetic field, the space charge limited current of diode is about half of the current without external applied magnetic field. In conditions without external applied magnetic field, radius of beam at anode surface and enhancement factor of space charge limited current both tend to decrease with increasing diode current.
Magnetic field affects strongly characteristics of spherical cathode diode. The numerical research shows that the effect of magnetic field (include self-magnetic field and external magnetic field) on diode takes place via varying the tracks of electron beam. The space charge limited current decreases as external applied magnetic field increases. With intense enough external applied magnetic field, the space charge limited current of diode is about half of the current without external applied magnetic field. In conditions without external applied magnetic field, radius of beam at anode surface and enhancement factor of space charge limited current both tend to decrease with increasing diode current.
2004,
16.
Abstract:
In this paper, the pulse shortening phenomena in relativistic backward wave oscillator(RBWO) are studied by means of the particle-in-cell method under two conditions of filling He gas or remaining background gas in the tube. The calculation results predict that the background gas in the tube is one but not the most important factor resulting in pulse shortening, and in order to broaden the pulse width of the gas-filled RBWO, the pressure of the filled gas must be controlled in a proper value. The intense electric field RF breakdown inside the tube and gas molecule explosive emission on inner surface of the slow wave system may be more important factors resulting in the pulse shortening phenomena in the high power microwave tube．
In this paper, the pulse shortening phenomena in relativistic backward wave oscillator(RBWO) are studied by means of the particle-in-cell method under two conditions of filling He gas or remaining background gas in the tube. The calculation results predict that the background gas in the tube is one but not the most important factor resulting in pulse shortening, and in order to broaden the pulse width of the gas-filled RBWO, the pressure of the filled gas must be controlled in a proper value. The intense electric field RF breakdown inside the tube and gas molecule explosive emission on inner surface of the slow wave system may be more important factors resulting in the pulse shortening phenomena in the high power microwave tube．
2004,
16.
Abstract:
The coaxial output-cavity with large coupling holes is often used in the high power microwave devices. The structure of this cavity is three dimensional with travelling wave boundary, and it is very difficult to calculate its high frequency characteristics by lumped parameters and numerical methods. On this condition, a kind of analytical method is developed in this paper. According to equivalent principle of field the cavity is divided into five regular regions. The field in each region is produced by proper surface magnetic current density on the common interface and can be expressed as integral of Green functions. The magnetic fields of two adjacent regions are then matched on the common interface to obtain a set of integral equations. From the integral equations the resonant frequency
The coaxial output-cavity with large coupling holes is often used in the high power microwave devices. The structure of this cavity is three dimensional with travelling wave boundary, and it is very difficult to calculate its high frequency characteristics by lumped parameters and numerical methods. On this condition, a kind of analytical method is developed in this paper. According to equivalent principle of field the cavity is divided into five regular regions. The field in each region is produced by proper surface magnetic current density on the common interface and can be expressed as integral of Green functions. The magnetic fields of two adjacent regions are then matched on the common interface to obtain a set of integral equations. From the integral equations the resonant frequency
2004,
16.
Abstract:
Maxwell's equations combined with heat transport equation have been solved by using FDTD with the leapfrog technique to simulate the microwave heating to water. The temperature distribution of water in the beaker is obtained.The efficiency of microwave heating with random phase and random frequency microwave power generators is studied.The absorbed quantity of heat by water and the temperature rising using the synthesis generators are compared with the results of normal microwave generator. The results show that we can achieve more homogeneous distribution of temperature and higher absorbed quantity of heat by using the synethesis of random phase microwave power generators.But this effect is not significant by using the synthesis of random frequency microwave power generators.
Maxwell's equations combined with heat transport equation have been solved by using FDTD with the leapfrog technique to simulate the microwave heating to water. The temperature distribution of water in the beaker is obtained.The efficiency of microwave heating with random phase and random frequency microwave power generators is studied.The absorbed quantity of heat by water and the temperature rising using the synthesis generators are compared with the results of normal microwave generator. The results show that we can achieve more homogeneous distribution of temperature and higher absorbed quantity of heat by using the synethesis of random phase microwave power generators.But this effect is not significant by using the synthesis of random frequency microwave power generators.
2004,
16.
Abstract:
The illumination of a 3D human body model by electromagnetic pulse (EMP) is numerically analyzed with frequency-dependence time-domain finitedifference ((FD)２TD) method. The fields in the body exhibit a strong dependence on the rise time of the illuminating pulses. Compared with the incident EMP, the transmitted pulses are narrower in width. No apparent relation between the absorbed energy and the incident energy density is observed, which is much different from that of the harmonic fields. Though the absorbed energy is far below the existing safety limit, the cell in experiment shows a growth inhibition. This phenomenon combined with the numerical results suggests that the safety assessment based on energy absorption is questionable．
The illumination of a 3D human body model by electromagnetic pulse (EMP) is numerically analyzed with frequency-dependence time-domain finitedifference ((FD)２TD) method. The fields in the body exhibit a strong dependence on the rise time of the illuminating pulses. Compared with the incident EMP, the transmitted pulses are narrower in width. No apparent relation between the absorbed energy and the incident energy density is observed, which is much different from that of the harmonic fields. Though the absorbed energy is far below the existing safety limit, the cell in experiment shows a growth inhibition. This phenomenon combined with the numerical results suggests that the safety assessment based on energy absorption is questionable．
2004,
16.
Abstract:
It is found that frequency tunability of the modulated current is related to periodicity of the Bessel's function of first kind.Ｒesponding to a same numerical values of the Bessel's function, there may be several numerical values of argument of the Bessel's function．Ｔhe frequency of the modulated current depends on the distance between the medium cavity and extract cavity, and the travel velocity of the electron beam, and so on,which are included in the argument of the Bessel's function. The theoretical estimations agree very well with the experimental results. The radiation frequency tunability of the relativistic klystron amplifier still depends on design of the extract cavity．
It is found that frequency tunability of the modulated current is related to periodicity of the Bessel's function of first kind.Ｒesponding to a same numerical values of the Bessel's function, there may be several numerical values of argument of the Bessel's function．Ｔhe frequency of the modulated current depends on the distance between the medium cavity and extract cavity, and the travel velocity of the electron beam, and so on,which are included in the argument of the Bessel's function. The theoretical estimations agree very well with the experimental results. The radiation frequency tunability of the relativistic klystron amplifier still depends on design of the extract cavity．
2004,
16.
Abstract:
In this paper, FDTD method incorporated with periodic boundary condition is applied to solve the near fields for dielectric gratings with plane wave illumination. Then the diffraction characteristics of transmission gratings are analyzed. The size of domain to be solved is restricted to a single cell of the dielectric periodic structure. Owing to the presence of interface of dielectric and air, it is required to impose three waves, including incident plane wave, reflected and transmitted waves at the total-scattered field boundary. The method is applied to study the diffraction characteristics of dielectric gratings with rectangular and trapezoid shapes. The presented scheme is useful to study the diffraction problem of dielectric gratings with arbitrary shape and complicated configuration
In this paper, FDTD method incorporated with periodic boundary condition is applied to solve the near fields for dielectric gratings with plane wave illumination. Then the diffraction characteristics of transmission gratings are analyzed. The size of domain to be solved is restricted to a single cell of the dielectric periodic structure. Owing to the presence of interface of dielectric and air, it is required to impose three waves, including incident plane wave, reflected and transmitted waves at the total-scattered field boundary. The method is applied to study the diffraction characteristics of dielectric gratings with rectangular and trapezoid shapes. The presented scheme is useful to study the diffraction problem of dielectric gratings with arbitrary shape and complicated configuration
