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RSS2005 Vol. 17, No. 07
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2005,
17.
Abstract:
Based on the theory of thermal elasticity of spherical symmetry, the laser-induced temperature rise and stress in silica glass or K9 glass, which contain high laser-absorptive platinum inclusion, are calculated from heat conduction and thermal stress equations. Phase change of the inclusion is considered. The optical glass containing inclusion is found to be damaged mainly by either thermal stress or the pressure resulted from boiling of the inclusion. Because of the difference in thermal and mechanical properties between silica glass and K9 glass, the thermal stress in silica glass will not be enough to make it damage before the inclusion vaporizes, and only the pressure due to the inclusion's boiling will serve as the main damage source. While in K9 glass, before the inclusion boils, the
Based on the theory of thermal elasticity of spherical symmetry, the laser-induced temperature rise and stress in silica glass or K9 glass, which contain high laser-absorptive platinum inclusion, are calculated from heat conduction and thermal stress equations. Phase change of the inclusion is considered. The optical glass containing inclusion is found to be damaged mainly by either thermal stress or the pressure resulted from boiling of the inclusion. Because of the difference in thermal and mechanical properties between silica glass and K9 glass, the thermal stress in silica glass will not be enough to make it damage before the inclusion vaporizes, and only the pressure due to the inclusion's boiling will serve as the main damage source. While in K9 glass, before the inclusion boils, the
2005,
17.
Abstract:
A physical model of InSb(PV) detector irradiated by CW laser was established. The distribution of temperature was studied by Gaussian beam with 2-D thermal model. The relationship between the temperature transformation and irradiation time was obtained. By numerical method, it was found that the damage of InSb material irradiated by CW laser was melt, and it took place firstly at the center of the laser-facing surface. The higher the laser power was, the less damage time was needed. With the same laser power density, thinner sub needed less irradiation time. For a definite sub, the damage threshold of laser was higher than a certain Imin. Whereas Imin was higher for thinner sub. To improve the anti-irradiation ability, it was necessary to diminish the thickness of sub. Additionally, the ca
A physical model of InSb(PV) detector irradiated by CW laser was established. The distribution of temperature was studied by Gaussian beam with 2-D thermal model. The relationship between the temperature transformation and irradiation time was obtained. By numerical method, it was found that the damage of InSb material irradiated by CW laser was melt, and it took place firstly at the center of the laser-facing surface. The higher the laser power was, the less damage time was needed. With the same laser power density, thinner sub needed less irradiation time. For a definite sub, the damage threshold of laser was higher than a certain Imin. Whereas Imin was higher for thinner sub. To improve the anti-irradiation ability, it was necessary to diminish the thickness of sub. Additionally, the ca
2005,
17.
Abstract:
The principle of a new one dimensional scanning apparatus named fixed angle plane reflective mirrors has been deduced and its optimized parameters of typical scanning distance of 10 cm and 6 cm have been calculated. Based on this scanning apparatus, one dimensional scanning measurement apparatus for chemical laser small signal gain coefficient has been designed and manufactured. The apparatus can embody two aspects, small size and convenience of utility. It can meet the need for continue wave DF/HF chemical laser research. If some improvement is made to the scanning components, the measurement apparatus could be used in CO2 laser and COIL research.
The principle of a new one dimensional scanning apparatus named fixed angle plane reflective mirrors has been deduced and its optimized parameters of typical scanning distance of 10 cm and 6 cm have been calculated. Based on this scanning apparatus, one dimensional scanning measurement apparatus for chemical laser small signal gain coefficient has been designed and manufactured. The apparatus can embody two aspects, small size and convenience of utility. It can meet the need for continue wave DF/HF chemical laser research. If some improvement is made to the scanning components, the measurement apparatus could be used in CO2 laser and COIL research.
2005,
17.
Abstract:
A double pulse trigger was designed，and the interval of the trigger pulse controlling the TEA laser high voltage switch could be adjusted from 5 ms to 100 ms to simulate different operating repetition rate of the TEA CO2 laser. By this means, the laser repetition rate was accurately controlled. The momentum coupling coefficients for the air-breathing mode laser propulsion were studied with a parabolic light craft model. It was found in the experiment that the momentum coupling coefficients decreased when the laser repetition rate increased, while the increment of the momentum coupling coefficients increased in unit time. The reason might be that the air as the propellant could not be supplied enough for the high laser pulse repetition rate, which would weaken the effect of the propulsion.
A double pulse trigger was designed，and the interval of the trigger pulse controlling the TEA laser high voltage switch could be adjusted from 5 ms to 100 ms to simulate different operating repetition rate of the TEA CO2 laser. By this means, the laser repetition rate was accurately controlled. The momentum coupling coefficients for the air-breathing mode laser propulsion were studied with a parabolic light craft model. It was found in the experiment that the momentum coupling coefficients decreased when the laser repetition rate increased, while the increment of the momentum coupling coefficients increased in unit time. The reason might be that the air as the propellant could not be supplied enough for the high laser pulse repetition rate, which would weaken the effect of the propulsion.
2005,
17.
Abstract:
The water vapor content in COIL was measured by absorption spectroscopy. Measurement results showed that the change of water vapor content due to the variation of the basic hydrogen peroxide (BHP) temperature could be ignored during normal operation. The water vapor content rose with the increasing of buffer gas flow rate. The gas flow velocity was the main factor that affected the water vapor content in COIL.
The water vapor content in COIL was measured by absorption spectroscopy. Measurement results showed that the change of water vapor content due to the variation of the basic hydrogen peroxide (BHP) temperature could be ignored during normal operation. The water vapor content rose with the increasing of buffer gas flow rate. The gas flow velocity was the main factor that affected the water vapor content in COIL.
2005,
17.
Abstract:
The wavefront distribution and the dynamic wavefront change of laser beam traversing a supersonic flow could be measured with Hartmann-Shack wavefront sensor. The centroid shift and the far-field distribution of laser beam could be obtained by further analyzing and calculating the experimental data. The experimental principle of laser beam traversing a supersonic flow was given. Wavefront aberration under different flow conditions was obtained by adopting Zernike mode-construction theory. The PV and RMS curve, Zernike aberration coefficient, Strehl ratio and circle energy were presented. Experimental results show that the establishing process, the stablizing process and the ending process of the supersonic flow can be measured and analyzed with H-S wavefront sensor. Comparing the data of n
The wavefront distribution and the dynamic wavefront change of laser beam traversing a supersonic flow could be measured with Hartmann-Shack wavefront sensor. The centroid shift and the far-field distribution of laser beam could be obtained by further analyzing and calculating the experimental data. The experimental principle of laser beam traversing a supersonic flow was given. Wavefront aberration under different flow conditions was obtained by adopting Zernike mode-construction theory. The PV and RMS curve, Zernike aberration coefficient, Strehl ratio and circle energy were presented. Experimental results show that the establishing process, the stablizing process and the ending process of the supersonic flow can be measured and analyzed with H-S wavefront sensor. Comparing the data of n
2005,
17.
Abstract:
Multi-order Stokes generation in pure CH4 and its He/Ar mixture pumped by a pulsed Nd:YAG laser at 355 nm were investigated. Maximum energy conversion efficiencies as high as 71% and 38% (i.e. quantum efficiency of 79% and 48%), much higher than those reported in previous literatures, were attained under 2.5 MPa and 1 MPa for the first and second Stokes respectively. Under 0.5 MPa CH4, significant multi-wavelength outputs could be obtained with energy distribution of 3.6% at 322 nm, 24.5% at 355 nm, 24.3% at 396 nm, 22.3% at 448 nm, and 9.3% at 515 nm. High-pressure CH4 was good for highly efficient first Stokes conversion, while low-pressure CH4 was suitable for higher order Stokes generation. The experimental results were analyzed in detail in terms of cascade stimulated Raman scattering
Multi-order Stokes generation in pure CH4 and its He/Ar mixture pumped by a pulsed Nd:YAG laser at 355 nm were investigated. Maximum energy conversion efficiencies as high as 71% and 38% (i.e. quantum efficiency of 79% and 48%), much higher than those reported in previous literatures, were attained under 2.5 MPa and 1 MPa for the first and second Stokes respectively. Under 0.5 MPa CH4, significant multi-wavelength outputs could be obtained with energy distribution of 3.6% at 322 nm, 24.5% at 355 nm, 24.3% at 396 nm, 22.3% at 448 nm, and 9.3% at 515 nm. High-pressure CH4 was good for highly efficient first Stokes conversion, while low-pressure CH4 was suitable for higher order Stokes generation. The experimental results were analyzed in detail in terms of cascade stimulated Raman scattering
2005,
17.
Abstract:
As for the temporal phase modulated broadband laser, by using some numerical techniques such as split-step Fourier transformation and fourth-order Runge-Kutta method, the effect of the intensity and bandwidth of the incident fundamental field, as well as that of the lengths of the KDP crystals on the third harmonic conversion efficiency of broadband laser have been discussed. The parameters of the mixers for the scheme of one type I doubler, one type II mixer and one type I mixer in quadrature have been optimized. The results show that using the scheme of cascade crystals can improve the third harmonic conversion efficiency and increase the dynamic range of the broadband laser tripling. For the bandwidth of 1.11 nm and the incident fundamental intensity between 3 GW/cm2 and 8 GW/cm2, the t
As for the temporal phase modulated broadband laser, by using some numerical techniques such as split-step Fourier transformation and fourth-order Runge-Kutta method, the effect of the intensity and bandwidth of the incident fundamental field, as well as that of the lengths of the KDP crystals on the third harmonic conversion efficiency of broadband laser have been discussed. The parameters of the mixers for the scheme of one type I doubler, one type II mixer and one type I mixer in quadrature have been optimized. The results show that using the scheme of cascade crystals can improve the third harmonic conversion efficiency and increase the dynamic range of the broadband laser tripling. For the bandwidth of 1.11 nm and the incident fundamental intensity between 3 GW/cm2 and 8 GW/cm2, the t
2005,
17.
Abstract:
The mechanical behavior and tensile spallation of pure aluminium subjected to intense laser irradiation were studied experimentally. The thicknesses of the samples are 200 μm and 485 μm, respectively.The laser irradiation intensity was in the range of 1010~1011 W·cm-2 with the full-width a half maximum of 10 ns. The free surface velocity of the shocked samples in the 242~1 125 m·s-1 range was measured by push-pull VISAR (velocity interferometer system for any reflector), which contained lots of information about the damage evolution and the influence on the mechanical behavior. The ablation pressure obtained on the front surface of the targets was in the range of 2.0~13.4 GPa. Based on the experimental and one dimension strain conditions, the linear relationship between the ablation pr
The mechanical behavior and tensile spallation of pure aluminium subjected to intense laser irradiation were studied experimentally. The thicknesses of the samples are 200 μm and 485 μm, respectively.The laser irradiation intensity was in the range of 1010~1011 W·cm-2 with the full-width a half maximum of 10 ns. The free surface velocity of the shocked samples in the 242~1 125 m·s-1 range was measured by push-pull VISAR (velocity interferometer system for any reflector), which contained lots of information about the damage evolution and the influence on the mechanical behavior. The ablation pressure obtained on the front surface of the targets was in the range of 2.0~13.4 GPa. Based on the experimental and one dimension strain conditions, the linear relationship between the ablation pr
2005,
17.
Abstract:
Experiment of the double-clad Yb-doped fiber amplifiers is discussed. The signal with 7 mW average power at 25.4 MHz repetition rate is amplified to 505 mW by using 0.5 m length of double-clad Yb-doped fiber when launched pumping power is 1.9 W, corresponding to a pulse energy of 19.8 nJ. The width of the pulses is compressed to about 2.7 ps by grating pair compressor.
Experiment of the double-clad Yb-doped fiber amplifiers is discussed. The signal with 7 mW average power at 25.4 MHz repetition rate is amplified to 505 mW by using 0.5 m length of double-clad Yb-doped fiber when launched pumping power is 1.9 W, corresponding to a pulse energy of 19.8 nJ. The width of the pulses is compressed to about 2.7 ps by grating pair compressor.
2005,
17.
Abstract:
As a new tool to detect atmosphere, lidar can derive the value of visibility by directly collecting the scatterd laser from the atmosphere. It makes lidar become a main instrument for measuring visibility. The schematic diagram and key parameters from the mobile Raman-Mie scattering lidar (RML) are given, and the slope method for getting visibility from data collected by lidar is presented.A practical experiment is conducted in Mianyang and the result is compared with that by Belfort visibility sensor.The results show that RML lidar has high reliability and is precise. The error of the measurement is less than 20%．
As a new tool to detect atmosphere, lidar can derive the value of visibility by directly collecting the scatterd laser from the atmosphere. It makes lidar become a main instrument for measuring visibility. The schematic diagram and key parameters from the mobile Raman-Mie scattering lidar (RML) are given, and the slope method for getting visibility from data collected by lidar is presented.A practical experiment is conducted in Mianyang and the result is compared with that by Belfort visibility sensor.The results show that RML lidar has high reliability and is precise. The error of the measurement is less than 20%．
2005,
17.
Abstract:
Target detection in a sequence of image is difficult when this target is small, faint, and obscured. In this paper, a method based on wavelet multi-resolution analysis and data fusion technology is presented for faint-target detection. The detection method is put forward with the consideration of the practicality of the method, especially while the image involves the complex background and a lot of noise. First, the image is decomposed using wavelet transform. The second part of the algorithm performs a data fusion using the sub-images of different resolution. It is shown that the algorithm can detect the faint target with accuracy and stabilization in the experiment using real images. The size of these experimental images is 256×256 pixels, and the size of target in the image is under 10
Target detection in a sequence of image is difficult when this target is small, faint, and obscured. In this paper, a method based on wavelet multi-resolution analysis and data fusion technology is presented for faint-target detection. The detection method is put forward with the consideration of the practicality of the method, especially while the image involves the complex background and a lot of noise. First, the image is decomposed using wavelet transform. The second part of the algorithm performs a data fusion using the sub-images of different resolution. It is shown that the algorithm can detect the faint target with accuracy and stabilization in the experiment using real images. The size of these experimental images is 256×256 pixels, and the size of target in the image is under 10
2005,
17.
Abstract:
The metallized film pulse capacitor is a key component of the inertial confinement laser fusion facility. For the high reliability capacitors, it is difficult to assess the reliability by using the traditional time-to-failure analysis method. By analyzing degradation mechanism of the metallized film capacitor, this paper presents a degradation failure model in which parameters can be estimated from the performance degradation measures of the capacitor. The estimation values of the unknown parameters in this model are 0.000 119 4 and 0.006 7, respectively. Both the failure probability density function (PDF) and the cumulative distribution function (CDF) can be presented by this degradation failure model. Based on these estimation values and the PDF/CDF, the reliability model of the metalliz
The metallized film pulse capacitor is a key component of the inertial confinement laser fusion facility. For the high reliability capacitors, it is difficult to assess the reliability by using the traditional time-to-failure analysis method. By analyzing degradation mechanism of the metallized film capacitor, this paper presents a degradation failure model in which parameters can be estimated from the performance degradation measures of the capacitor. The estimation values of the unknown parameters in this model are 0.000 119 4 and 0.006 7, respectively. Both the failure probability density function (PDF) and the cumulative distribution function (CDF) can be presented by this degradation failure model. Based on these estimation values and the PDF/CDF, the reliability model of the metalliz
2005,
17.
Abstract:
Copper nanoparticles were synthesized by the flow-levitation method and they were coated with the carbon-and-hydrogen films through the hollow-cathode glow discharge(HCGD). The growth mechanism of the coating films was described. The HCGD with a voltage of 450 V was used for producing CH plasma. The input fluxes of H2 and CH4 were 12 ml/min and 6 ml/min, respectively. The distance from the sample step to the bottom of the cathode was 2 cm. The working pressure was 100 Pa and the deposition velocity was 7.5 nm/min. The coated Cu nanoparticles and uncoated ones were observed with transmission electron microscopy. Cu nanoparticles were spherical but not very well defined, and the particle size ranged from 10 nm to 100 nm in diameter. The coating thickness was about 15 nm for most of the nanop
Copper nanoparticles were synthesized by the flow-levitation method and they were coated with the carbon-and-hydrogen films through the hollow-cathode glow discharge(HCGD). The growth mechanism of the coating films was described. The HCGD with a voltage of 450 V was used for producing CH plasma. The input fluxes of H2 and CH4 were 12 ml/min and 6 ml/min, respectively. The distance from the sample step to the bottom of the cathode was 2 cm. The working pressure was 100 Pa and the deposition velocity was 7.5 nm/min. The coated Cu nanoparticles and uncoated ones were observed with transmission electron microscopy. Cu nanoparticles were spherical but not very well defined, and the particle size ranged from 10 nm to 100 nm in diameter. The coating thickness was about 15 nm for most of the nanop
2005,
17.
Abstract:
DPFA new type of differential interferometer using a defocused 4f imaging system is described. The interferometer is stable and easy to adjust with a ring structure. The shear amount and fringe spacing can be adjusted independently with the defocused 4f design. High spatial resolution and readable fringes can be obtained simultaneously in dense plasma diagnosis. As an example, the DPF plasma was diagnosed by the 4f system. Interferograms were acquired at different time during pinch process. The radial distributions of local electron density were calculated. The maximum local electron density above the anode end was measured about 1.2×1019 cm-3 and that of the outer plasma shell 2×1018 cm-3 when plasma began pinching.
DPFA new type of differential interferometer using a defocused 4f imaging system is described. The interferometer is stable and easy to adjust with a ring structure. The shear amount and fringe spacing can be adjusted independently with the defocused 4f design. High spatial resolution and readable fringes can be obtained simultaneously in dense plasma diagnosis. As an example, the DPF plasma was diagnosed by the 4f system. Interferograms were acquired at different time during pinch process. The radial distributions of local electron density were calculated. The maximum local electron density above the anode end was measured about 1.2×1019 cm-3 and that of the outer plasma shell 2×1018 cm-3 when plasma began pinching.
2005,
17.
Abstract:
With inorganic compounds, hollow glass microsphere (HGM) of above 10% molar ratio K2O was prepared by liquid-droplet method.The glass forming oxides content in solutions and technical conditions of preparing were optimized and selected. The molar ratios of glass forming oxides in shell of HGM were analyzed by means of EDAX device.The results showed that the diameter, wall thickness, concentricity and sphericity of HGM satisfied the physical experiments on the SG II device.Test value of molar ratio of glass forming oxides in HGM were closed to theoretic value.
With inorganic compounds, hollow glass microsphere (HGM) of above 10% molar ratio K2O was prepared by liquid-droplet method.The glass forming oxides content in solutions and technical conditions of preparing were optimized and selected. The molar ratios of glass forming oxides in shell of HGM were analyzed by means of EDAX device.The results showed that the diameter, wall thickness, concentricity and sphericity of HGM satisfied the physical experiments on the SG II device.Test value of molar ratio of glass forming oxides in HGM were closed to theoretic value.
2005,
17.
Abstract:
The properties and derivation of defects in thin film are introduced in this paper. The influence of the deposition rate of YbF3 on the surface defect density of infrared laser thin film is analyzed. The appropriate deposition rate of YbF3 on the thin film is put forward. The result shows that the nodules and concave holes are the main defects in the infrared laser thin film, and that the defect density decreases with the decrease of deposition rate of YbF3. The defect density is only 0.000 675 when deposition rates are 0.4 nm/s for ZnS and 0.2 nm/s for YbF3, respectively.
The properties and derivation of defects in thin film are introduced in this paper. The influence of the deposition rate of YbF3 on the surface defect density of infrared laser thin film is analyzed. The appropriate deposition rate of YbF3 on the thin film is put forward. The result shows that the nodules and concave holes are the main defects in the infrared laser thin film, and that the defect density decreases with the decrease of deposition rate of YbF3. The defect density is only 0.000 675 when deposition rates are 0.4 nm/s for ZnS and 0.2 nm/s for YbF3, respectively.
2005,
17.
Abstract:
The ultra-fine molybdenum wire is often used for Z-pinch experiment. To improve the performance of the molybdenum wire, the sulfite pulse gilding technique was used to plate a compact gold layer on the wire. The technological conditions were optimized to ensure the surface quality of the molybdenum wire, including the cathode current density being 2 mA/cm2, the pH value of the solution being 8.5, and the temperature of the solution being 40 ℃. The surface of the molybdenum wire was observed by a scan electron microscope. The bind-force between the gold layer and the molybdenum wire was tested with the nick method. The results show that with the optimized technique the molybdenum wire of less than 15 μm in diameter can be plated with a gold layer of 0.6~2.5 μm thick and the gilt molybden
The ultra-fine molybdenum wire is often used for Z-pinch experiment. To improve the performance of the molybdenum wire, the sulfite pulse gilding technique was used to plate a compact gold layer on the wire. The technological conditions were optimized to ensure the surface quality of the molybdenum wire, including the cathode current density being 2 mA/cm2, the pH value of the solution being 8.5, and the temperature of the solution being 40 ℃. The surface of the molybdenum wire was observed by a scan electron microscope. The bind-force between the gold layer and the molybdenum wire was tested with the nick method. The results show that with the optimized technique the molybdenum wire of less than 15 μm in diameter can be plated with a gold layer of 0.6~2.5 μm thick and the gilt molybden
2005,
17.
Abstract:
Lightning electromagnetic pulse field (LEMP) was simulated to study its effect on naked radio fuze. The voltage wave from MARX generator was injected into GTEM cell to simulate the electric field of LEMP, and the pulse current wave from lightning surge generator was injected into loop to simulate the magnetic field in the loop. Some radio fuze was chosen as samples to test its deposited security in strong LEMP environment. The experimental results show that in severe condition the lightning electric field can attaint the high frequency groupware and might disable the fuze to produce detecting signal. The lightning electric field can destroy the demodulation circuitry and cause the demodulation voltage out of gear. The lightning magnetic field has no evident effect on the fuze.
Lightning electromagnetic pulse field (LEMP) was simulated to study its effect on naked radio fuze. The voltage wave from MARX generator was injected into GTEM cell to simulate the electric field of LEMP, and the pulse current wave from lightning surge generator was injected into loop to simulate the magnetic field in the loop. Some radio fuze was chosen as samples to test its deposited security in strong LEMP environment. The experimental results show that in severe condition the lightning electric field can attaint the high frequency groupware and might disable the fuze to produce detecting signal. The lightning electric field can destroy the demodulation circuitry and cause the demodulation voltage out of gear. The lightning magnetic field has no evident effect on the fuze.
2005,
17.
Abstract:
This work focused on the metal posts' scattering calculation and design in coaxial waveguide (CWG), which are useful in many high-power microwave devices. The calculation model was constructed by equating CWG with rectangular waveguide. The scattering formula was deduced by Integral Equation Method, which was validated by Finite Element Method. The calculation and experiment results show that the posts will excite a series of TE(mn)1 modes in CWG when TEM mode is inputted. While the number of the posts is greater than the ratio of the CWG's average perimeter to wavelength, all of the TE(mn)1 modes are evanescent, with only TEM mode being outputted. The reflection coefficient of TEM mode increases with number or radius of the posts, and is in inverse proportion to frequency.
This work focused on the metal posts' scattering calculation and design in coaxial waveguide (CWG), which are useful in many high-power microwave devices. The calculation model was constructed by equating CWG with rectangular waveguide. The scattering formula was deduced by Integral Equation Method, which was validated by Finite Element Method. The calculation and experiment results show that the posts will excite a series of TE(mn)1 modes in CWG when TEM mode is inputted. While the number of the posts is greater than the ratio of the CWG's average perimeter to wavelength, all of the TE(mn)1 modes are evanescent, with only TEM mode being outputted. The reflection coefficient of TEM mode increases with number or radius of the posts, and is in inverse proportion to frequency.
2005,
17.
Abstract:
This paper provides a simple technique to design and optimize the spiral waveguide of Gyro-TWT. The dispersion characteristics of helical waveguide was given out. The structure of waveguide was modeled by CAD and it′s dispersion curve was calculated by MAFIA using quasi-periodic boundary condition. The modes were calculated alternation 30° phaseshift from -180° to 180°. This method leads to a good agreement with the result of dispersion equation over 8.3~10.6 GHz, and the maximum relative deviation is below 0.5%. For a rather broad frequency band around the point where the longitudinal wavenumber is equal to zero, the slope of the dispersion curve trends to a positive constant. As a micro-wave amplifier, Gyro-TWT using spiral waveguide has a good potential in improving its effectivenes
This paper provides a simple technique to design and optimize the spiral waveguide of Gyro-TWT. The dispersion characteristics of helical waveguide was given out. The structure of waveguide was modeled by CAD and it′s dispersion curve was calculated by MAFIA using quasi-periodic boundary condition. The modes were calculated alternation 30° phaseshift from -180° to 180°. This method leads to a good agreement with the result of dispersion equation over 8.3~10.6 GHz, and the maximum relative deviation is below 0.5%. For a rather broad frequency band around the point where the longitudinal wavenumber is equal to zero, the slope of the dispersion curve trends to a positive constant. As a micro-wave amplifier, Gyro-TWT using spiral waveguide has a good potential in improving its effectivenes
2005,
17.
Abstract:
The physical mechanism of delayed breakdown diode(DBD) was analyzed. Considering both the amplitude and the rise time of the output pulse across the load, the characteristics of DBD with different structure parameters and physical parameters (length, area, doping and the stimulating source) were simulated. The simulation results show that there exists a minimum value for rise time with respect to both the area of the DBD and the load resistance. The minimum value should be adopted in design. Theoretically the optimum length of n region should be the maximum punching through length. The lengths of p+ region and n+ region have little influence on the DBD performance, which should be greater than their punching through lengths. And their doping density, the higher the better. As regard to the
The physical mechanism of delayed breakdown diode(DBD) was analyzed. Considering both the amplitude and the rise time of the output pulse across the load, the characteristics of DBD with different structure parameters and physical parameters (length, area, doping and the stimulating source) were simulated. The simulation results show that there exists a minimum value for rise time with respect to both the area of the DBD and the load resistance. The minimum value should be adopted in design. Theoretically the optimum length of n region should be the maximum punching through length. The lengths of p+ region and n+ region have little influence on the DBD performance, which should be greater than their punching through lengths. And their doping density, the higher the better. As regard to the
2005,
17.
Abstract:
The inter-related parameters of higher-order TM mode was investigated of microwave cylindrical coaxial cavities. Using FORTRAN program, parameters of the cavity were obtained, such as cavities' size, orders of TM mode, frequencies, radii of positions of longitudinal maximum electric field intensity and characteristic impedances in the cavities etc. The calculated result was in good agreement with that simulated by ISFEL 3D. Database used for optimum seeking can be gotten instantly this way instead of the time-consuming emulation by trial and error method.
The inter-related parameters of higher-order TM mode was investigated of microwave cylindrical coaxial cavities. Using FORTRAN program, parameters of the cavity were obtained, such as cavities' size, orders of TM mode, frequencies, radii of positions of longitudinal maximum electric field intensity and characteristic impedances in the cavities etc. The calculated result was in good agreement with that simulated by ISFEL 3D. Database used for optimum seeking can be gotten instantly this way instead of the time-consuming emulation by trial and error method.
2005,
17.
Abstract:
The beam parameters of high energy and high current LIA are very important for the debugging work. For its ultra-fast response and high resolution, OTR is used to measure both spatial and angular profiles of an electron beam. A time-resolved measurement result of an electron beam produced by LIA can provide much more detailed information．Such a time-resolved measurement system for electron beam profile using OTR has been developed recently in the Institute of Fluid Physics of CAEP and has been put into practice. Typical time-resolved measurement results of an electron beam produced by 12 MeV LIA are shown in the paper. Many phenomena are observed for the first time. This system can capture 8 frame images at a time in the minimum time interval of 10ns while the exposure time is 3 ns．The f
The beam parameters of high energy and high current LIA are very important for the debugging work. For its ultra-fast response and high resolution, OTR is used to measure both spatial and angular profiles of an electron beam. A time-resolved measurement result of an electron beam produced by LIA can provide much more detailed information．Such a time-resolved measurement system for electron beam profile using OTR has been developed recently in the Institute of Fluid Physics of CAEP and has been put into practice. Typical time-resolved measurement results of an electron beam produced by 12 MeV LIA are shown in the paper. Many phenomena are observed for the first time. This system can capture 8 frame images at a time in the minimum time interval of 10ns while the exposure time is 3 ns．The f
2005,
17.
Abstract:
The paper introduced a dispenser cathode (411 M) which was 55 mm in diameter. A 200 kV long pulsed power generator with 2 μs flattop based on Marx-PEN and system with heat and voltage insulation were built. A 52 A space charge limited current was gained, when the temperature was 1 165 ℃ and the filament current was 18 A on the cathode and the voltage of the pulse was 75 kV at the cathode test stand. Experimental results show that the current values is consistent with the numerical simulation. The experiment reveals that the deflated gas will influence the cathode emittion ability.
The paper introduced a dispenser cathode (411 M) which was 55 mm in diameter. A 200 kV long pulsed power generator with 2 μs flattop based on Marx-PEN and system with heat and voltage insulation were built. A 52 A space charge limited current was gained, when the temperature was 1 165 ℃ and the filament current was 18 A on the cathode and the voltage of the pulse was 75 kV at the cathode test stand. Experimental results show that the current values is consistent with the numerical simulation. The experiment reveals that the deflated gas will influence the cathode emittion ability.
2005,
17.
Abstract:
The 4 MV electrostatic accelerator consists of four parts, a high voltage system, an ion source and beam transmission system, a control system and a gas system. Some technical problems arose during the debugging of the accelerator. The ion source did not produce arc. The accelerator tube cracked. The control system was out of order. The transporting capacity of the charge belt degraded. The corresponding reasons were analyzed and some measures were adopted to solve the problems. The drawing voltage was raised to its predetermined position after the ion source produced arc and should be reduced to zero before turning off the accelerator. Transition flange was lathed and the accelerator tube was re-assembled. The control equipment at high voltage was shielded. TVS diodes were installed at th
The 4 MV electrostatic accelerator consists of four parts, a high voltage system, an ion source and beam transmission system, a control system and a gas system. Some technical problems arose during the debugging of the accelerator. The ion source did not produce arc. The accelerator tube cracked. The control system was out of order. The transporting capacity of the charge belt degraded. The corresponding reasons were analyzed and some measures were adopted to solve the problems. The drawing voltage was raised to its predetermined position after the ion source produced arc and should be reduced to zero before turning off the accelerator. Transition flange was lathed and the accelerator tube was re-assembled. The control equipment at high voltage was shielded. TVS diodes were installed at th
2005,
17.
Abstract:
The cooling time and cooling efficiency in electron cooling device strongly depend on the transverse temperature of electron beam. In order to reduce this temperature, a new type of cooling section solenoid composed of 68 coils was used in the HIRFL-CSR electron cooling device to produce a high parallelism magnetic field. With the Hall probe, the components of the magnetic field along the ion beam orbit were measured, and using the compass method the magnetic field parallelism in cooling section was measured. According to the measured results, the magnetic axis angle of each coil with respect to the geometric axis was regulated correspondingly. The magnetic field nonparallelism in the cooling section less than 1×10-4 was achieved and a magnetic induction strength of 0.078 T was obtained.
The cooling time and cooling efficiency in electron cooling device strongly depend on the transverse temperature of electron beam. In order to reduce this temperature, a new type of cooling section solenoid composed of 68 coils was used in the HIRFL-CSR electron cooling device to produce a high parallelism magnetic field. With the Hall probe, the components of the magnetic field along the ion beam orbit were measured, and using the compass method the magnetic field parallelism in cooling section was measured. According to the measured results, the magnetic axis angle of each coil with respect to the geometric axis was regulated correspondingly. The magnetic field nonparallelism in the cooling section less than 1×10-4 was achieved and a magnetic induction strength of 0.078 T was obtained.
2005,
17.
Abstract:
An electron gun was designed and the beam optics for a China-made 50 MW klystron was simulated. The electron gun ceramic cylinder was designed and optimized. The China-made cathode was replaced with an imported one to lessen evaporation and arcing. The high voltage (320 kV) of the cathode was increased to meet the klystron output power demand and a low electric field strength (22.1 kV／mm) electron gun was designed to avoid the high power operation which damaged the ceramic cylinder. The klystron output power was increased and life span extended.
An electron gun was designed and the beam optics for a China-made 50 MW klystron was simulated. The electron gun ceramic cylinder was designed and optimized. The China-made cathode was replaced with an imported one to lessen evaporation and arcing. The high voltage (320 kV) of the cathode was increased to meet the klystron output power demand and a low electric field strength (22.1 kV／mm) electron gun was designed to avoid the high power operation which damaged the ceramic cylinder. The klystron output power was increased and life span extended.
2005,
17.
Abstract:
RF superconducting cavities can work at CW mode or long pulse mode with high accelerating gradient. RF superconducting technology is widely used in particle accelerators. A lot of front scientific facilities are set up based on RF superconducting accelerators from low beta to high beta. RF superconductivity has become a most important technology in FEL and ERL. In the recent 30 years, the technology has made rapid progresses. The accelerating gradient can be over 40 MV/m by special treatments. High accelerating gradient is the front research in the field of RF superconductivity. EP + bake can provide an important method to increase the accelerating gradient. The accelerating gradient can increase by 3~4 MV/m after EP + bake treatment and the Q-drop is also improved. Recent developed dry tr
RF superconducting cavities can work at CW mode or long pulse mode with high accelerating gradient. RF superconducting technology is widely used in particle accelerators. A lot of front scientific facilities are set up based on RF superconducting accelerators from low beta to high beta. RF superconductivity has become a most important technology in FEL and ERL. In the recent 30 years, the technology has made rapid progresses. The accelerating gradient can be over 40 MV/m by special treatments. High accelerating gradient is the front research in the field of RF superconductivity. EP + bake can provide an important method to increase the accelerating gradient. The accelerating gradient can increase by 3~4 MV/m after EP + bake treatment and the Q-drop is also improved. Recent developed dry tr
2005,
17.
Abstract:
Experimental study on discharge characteristics of high pressure subnanosecond N2 switch was carried out by using a high voltage nanosecond generator in the article. The results show that when N2 pressure ranges from 3 to 10 MPa and gap distance ranges from 0.6 to 1.2 mm, the breakdown voltage of N2 gap increases as N2 pressure and gap distance increases, and saturates as N2 pressure increases. The highest breakdown electric field is about 2 MV/cm. The rise time of the output voltage of the high pressure subnanosecond N2 switch ranges 145~190 ps, and decreases as N2 pressure and gap distance increases.
Experimental study on discharge characteristics of high pressure subnanosecond N2 switch was carried out by using a high voltage nanosecond generator in the article. The results show that when N2 pressure ranges from 3 to 10 MPa and gap distance ranges from 0.6 to 1.2 mm, the breakdown voltage of N2 gap increases as N2 pressure and gap distance increases, and saturates as N2 pressure increases. The highest breakdown electric field is about 2 MV/cm. The rise time of the output voltage of the high pressure subnanosecond N2 switch ranges 145~190 ps, and decreases as N2 pressure and gap distance increases.
2005,
17.
Abstract:
The characteristics of different types of MPL were analyzed and the convolutional PML was chosen to truncate the open boundaries in numerical simulation of nuclear electromagnetic pulse from air explosions. On the basis of the split-field PML and the plane-wave solution of electromagnetic field in free space, the unsplit-field PML was constructed. By applying the convolutional theorem of Fourier transform, the discrete iterative equations of electromagnetic field components were presented in the CPML media under the two-dimension prolate-spheroidal coordinate system. The numerical results indicate that the method of CPML can largely decrease calculation errors of boundary fields.
The characteristics of different types of MPL were analyzed and the convolutional PML was chosen to truncate the open boundaries in numerical simulation of nuclear electromagnetic pulse from air explosions. On the basis of the split-field PML and the plane-wave solution of electromagnetic field in free space, the unsplit-field PML was constructed. By applying the convolutional theorem of Fourier transform, the discrete iterative equations of electromagnetic field components were presented in the CPML media under the two-dimension prolate-spheroidal coordinate system. The numerical results indicate that the method of CPML can largely decrease calculation errors of boundary fields.
2005,
17.
Abstract:
A circuit model for Yang accelerator's water transmission line and magnetically insulated transmission line (MITL) based on their impedance characteristics was employed to simulate the experiments, among which the one for a shorted load was perfectly modeled and the other for a wire array load however could not be accurately modeled until a series of load was introduced. With the aid of the model, the typical implosion characteristics of the wire array loads were discussed. The comparison of the calculated results by the model with the experimental ones indicates that the model is validated and is available for design and analysis of both the water transmission line and MITL.
A circuit model for Yang accelerator's water transmission line and magnetically insulated transmission line (MITL) based on their impedance characteristics was employed to simulate the experiments, among which the one for a shorted load was perfectly modeled and the other for a wire array load however could not be accurately modeled until a series of load was introduced. With the aid of the model, the typical implosion characteristics of the wire array loads were discussed. The comparison of the calculated results by the model with the experimental ones indicates that the model is validated and is available for design and analysis of both the water transmission line and MITL.
2005,
17.
Abstract:
The tune modulation due to power supply ripple of magnets has a strong destabilizing effects on non-linear motion. In order to investigate this effect on the dynamic aperture of HIRFL-CSRm, a tracking study was done. The impacts of quadrupole power supply ripple were modelled by modulating the linear Betatron oscillation tunes and the dynamic aperture was calculated through tracking particle one million turns in HIRFL-CSRm lattice. It turned out that the dynamic aperture decreased roughly linearly with the amplitude of the tune modulation. The dependence of the dynamic aperture on the frequency of the modulation was also studied, but it was relatively weak.
The tune modulation due to power supply ripple of magnets has a strong destabilizing effects on non-linear motion. In order to investigate this effect on the dynamic aperture of HIRFL-CSRm, a tracking study was done. The impacts of quadrupole power supply ripple were modelled by modulating the linear Betatron oscillation tunes and the dynamic aperture was calculated through tracking particle one million turns in HIRFL-CSRm lattice. It turned out that the dynamic aperture decreased roughly linearly with the amplitude of the tune modulation. The dependence of the dynamic aperture on the frequency of the modulation was also studied, but it was relatively weak.
2005,
17.
Abstract:
Single transmission line theory was introduced. Three PFLs were serially triggered to form a 3-pulse and a sequence of 3-pulse was produced along the same time axis. In the experiment, a 300 kV Marx generator was used to supply high voltage for 3 PFL, a coaxial switch was used, and the load was CuSO4 liquid resistance. A 3-pulse waveform was produced. The rising time was about 20 ns, the distance between two pulses about 300 ns and the pulse width about 120 ns. There were obvious differences in the amplitude among the 3-pulses, since Marx output were not triggered in the same time. Finally some projects for improving the waveform were introduced.
Single transmission line theory was introduced. Three PFLs were serially triggered to form a 3-pulse and a sequence of 3-pulse was produced along the same time axis. In the experiment, a 300 kV Marx generator was used to supply high voltage for 3 PFL, a coaxial switch was used, and the load was CuSO4 liquid resistance. A 3-pulse waveform was produced. The rising time was about 20 ns, the distance between two pulses about 300 ns and the pulse width about 120 ns. There were obvious differences in the amplitude among the 3-pulses, since Marx output were not triggered in the same time. Finally some projects for improving the waveform were introduced.
2005,
17.
Abstract:
Based on the constrained conjugate gradient algorithm, a regularization preconditioned constrained conjugate gradient algorithm (RPCCG) was proposed for image-reconstruction for radiography. The RPCCG used the Tikhonov regularization criterions to get the reconstruction equation. The equation was solved by using the preconditioned conjugate gradient algorithm, constrained with prior knowledge. Numerical experiment results show that in comparison with the FBP algorithm, RPCCG based on least square + smoothness criterion is more efficient in reconstruction quality and noise removal.
Based on the constrained conjugate gradient algorithm, a regularization preconditioned constrained conjugate gradient algorithm (RPCCG) was proposed for image-reconstruction for radiography. The RPCCG used the Tikhonov regularization criterions to get the reconstruction equation. The equation was solved by using the preconditioned conjugate gradient algorithm, constrained with prior knowledge. Numerical experiment results show that in comparison with the FBP algorithm, RPCCG based on least square + smoothness criterion is more efficient in reconstruction quality and noise removal.
2005,
17.
Abstract:
The relation between -3 dB frequency of amplitude-frequency characteristics and 10% to 90% risetime of unit-step response is studied for one- and two-stage resistive voltage dividers with and without inductance compensation. The product of the -3 dB frequency and the risetime for one-stage resistive voltage dividers without inductance compensation is the constant of 0.350. For two-stage dividers without compensation this product changes slightly near its average 0.349. For one-stage dividers with compensation the product is determined by overshoot and changes from 0.35 to 0.29 with overshoot from 0 to 10%. For two-stage dividers with compensation the product changes with overshoot and divider parameters, and the change at fixed overshoot less than 10% is about ±10%。When the time constant
The relation between -3 dB frequency of amplitude-frequency characteristics and 10% to 90% risetime of unit-step response is studied for one- and two-stage resistive voltage dividers with and without inductance compensation. The product of the -3 dB frequency and the risetime for one-stage resistive voltage dividers without inductance compensation is the constant of 0.350. For two-stage dividers without compensation this product changes slightly near its average 0.349. For one-stage dividers with compensation the product is determined by overshoot and changes from 0.35 to 0.29 with overshoot from 0 to 10%. For two-stage dividers with compensation the product changes with overshoot and divider parameters, and the change at fixed overshoot less than 10% is about ±10%。When the time constant
