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RSS2013 Vol. 25, No. 10
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2013,
25: 2477-2478.
doi: 10.3788/HPLPB20132510.2477
Abstract:
An all-fiber Tm-doped pulse laser with active mode-locking is demonstrated, the center wavelength is 1.95 m. The phase in the laser cavity was modulated by an electronic optical phase modulator, and an actively mode-locked pulse output with a repetition rate of 11.884 MHz was obtained, the pulse duration was 816 ps. Relaxation oscillation modulated stable pulse train with a repetition rate of 4-18 kHz was realized by adjusting the pump power, the frequency and amplitude of modulating signal. All the energy fluctuations of the stable pulse trains were less than 7%.
An all-fiber Tm-doped pulse laser with active mode-locking is demonstrated, the center wavelength is 1.95 m. The phase in the laser cavity was modulated by an electronic optical phase modulator, and an actively mode-locked pulse output with a repetition rate of 11.884 MHz was obtained, the pulse duration was 816 ps. Relaxation oscillation modulated stable pulse train with a repetition rate of 4-18 kHz was realized by adjusting the pump power, the frequency and amplitude of modulating signal. All the energy fluctuations of the stable pulse trains were less than 7%.
2013,
25: 2479-2486.
doi: 10.3788/HPLPB20132510.2479
Abstract:
The vibrating wire technique is used as an alignment method which carries out magnets alignment by measuring the magnetic field of the magnets. It is different from the alignment method based on the mechanical structure of the components. The vibrating wire technique demonstrates high measurement precision and high sensitivity. It can be used in many ways, such as for measuring the magnetic center of a single magnet, for magnet fiducialization, and for magnetic center alignment of several magnets. This article mainly introduces the principle, theoretical conclusions and the research overview of the vibrating wire technique.
The vibrating wire technique is used as an alignment method which carries out magnets alignment by measuring the magnetic field of the magnets. It is different from the alignment method based on the mechanical structure of the components. The vibrating wire technique demonstrates high measurement precision and high sensitivity. It can be used in many ways, such as for measuring the magnetic center of a single magnet, for magnet fiducialization, and for magnetic center alignment of several magnets. This article mainly introduces the principle, theoretical conclusions and the research overview of the vibrating wire technique.
2013,
25: 2487-2495.
doi: 10.3788/HPLPB20132510.2487
Abstract:
The basic characteristic of the pulsed power science and technology, which is widely applied to X-ray radiography, inertial confinement fusion and high energy density physics, is energy compressing, both temporally and spatially, to obtain high power density and extreme conditions in temperature, pressure and radiation. Vacuum power flow components are decisive for pulsed power systems. Physical fundamentals, key issues and researching status for vacuum power flow around the world are surveyed in this paper. The gap between object and status is analyzed for vacuum power flow investigations for Z-pinch fusion driver. Opinions and researching suggestions are presented.
The basic characteristic of the pulsed power science and technology, which is widely applied to X-ray radiography, inertial confinement fusion and high energy density physics, is energy compressing, both temporally and spatially, to obtain high power density and extreme conditions in temperature, pressure and radiation. Vacuum power flow components are decisive for pulsed power systems. Physical fundamentals, key issues and researching status for vacuum power flow around the world are surveyed in this paper. The gap between object and status is analyzed for vacuum power flow investigations for Z-pinch fusion driver. Opinions and researching suggestions are presented.
2013,
25: 2496-2500.
doi: 10.3788/HPLPB20132510.2496
Abstract:
The effects of refractive index and fiber core structure on energy distribution were studied by setting up laser transmission model in single mode fiber with Comsol and Matlab. First, the relationship between the fiber core, numerical aperture, normalized frequency and power fill factor was analyzed. Second, the energy density distribution of various designs for the core refractive index of single mode fiber was numerically simulated and compared. According to the calculation and the simulation results, it is concluded that central-dip fiber can enlarge mode area and lower the power density. Finally, due to the application requirement of high power fiber laser, the single mode central-dip fiber was designed with the wavelength of 1.064 m, the core diameter of 10 m, the concave diameter of 8 m, and the numerical aperture of 0.12, which provides an idea for the development of pump efficiency and the reduction of the energy density in fiber core.
The effects of refractive index and fiber core structure on energy distribution were studied by setting up laser transmission model in single mode fiber with Comsol and Matlab. First, the relationship between the fiber core, numerical aperture, normalized frequency and power fill factor was analyzed. Second, the energy density distribution of various designs for the core refractive index of single mode fiber was numerically simulated and compared. According to the calculation and the simulation results, it is concluded that central-dip fiber can enlarge mode area and lower the power density. Finally, due to the application requirement of high power fiber laser, the single mode central-dip fiber was designed with the wavelength of 1.064 m, the core diameter of 10 m, the concave diameter of 8 m, and the numerical aperture of 0.12, which provides an idea for the development of pump efficiency and the reduction of the energy density in fiber core.
2013,
25: 2501-2504.
doi: 10.3788/HPLPB20132510.2501
Abstract:
The conservation equations describing the movement of the plasma in the laser-supported detonation process are numerically calculated with the space-time conservation element and solution element method. The distributions of the pressure, the density, the temperature, the velocity and the absorption coefficient of the plasma at different time interval are given. The characters of the evolving plasma with different initial density are compared. It is concluded that, the absorption of laser is larger when the plasma has larger initial density. The laser energy can be better coupled to the target by modifying the initial density of the plasma, the duration of the laser pulses and the pulse interval.
The conservation equations describing the movement of the plasma in the laser-supported detonation process are numerically calculated with the space-time conservation element and solution element method. The distributions of the pressure, the density, the temperature, the velocity and the absorption coefficient of the plasma at different time interval are given. The characters of the evolving plasma with different initial density are compared. It is concluded that, the absorption of laser is larger when the plasma has larger initial density. The laser energy can be better coupled to the target by modifying the initial density of the plasma, the duration of the laser pulses and the pulse interval.
2013,
25: 2505-2510.
doi: 10.3788/HPLPB20132510.2505
Abstract:
The high frequency phase of near-field distorted wavefront is recovered using the successive iteration method. The variation of the recovery effect with the filter cutoff frequency is quantitatively analyzed. The influences of the noise disturbance of near-field and far-field intensities on the recovery effect are discussed. The results show that, with the increasing of the filter cutoff frequency, that is, with the increasing of the measurement requirement for the wavefront phase detector, the recovery effect of high frequency phase by using successive iteration method will be better. In addition, the recovery effect of high frequency phase becomes worse with the increasing of the noise disturbance of near-field or far-field intensity. Specifically, the influence of the noise disturbance of near-field intensity on the recovery effect is relatively small, whereas that of the noise disturbance of far-field intensity is more significant. In practical applications, in order to achieve better recovery effect of the near-field high frequency phase, the demand on the low-frequency phase measurement in near field should be required reasonably, and the measurement errors of the intensity distributions must be as low as possible, especially the influence of far-field noise disturbance should be small enough.
The high frequency phase of near-field distorted wavefront is recovered using the successive iteration method. The variation of the recovery effect with the filter cutoff frequency is quantitatively analyzed. The influences of the noise disturbance of near-field and far-field intensities on the recovery effect are discussed. The results show that, with the increasing of the filter cutoff frequency, that is, with the increasing of the measurement requirement for the wavefront phase detector, the recovery effect of high frequency phase by using successive iteration method will be better. In addition, the recovery effect of high frequency phase becomes worse with the increasing of the noise disturbance of near-field or far-field intensity. Specifically, the influence of the noise disturbance of near-field intensity on the recovery effect is relatively small, whereas that of the noise disturbance of far-field intensity is more significant. In practical applications, in order to achieve better recovery effect of the near-field high frequency phase, the demand on the low-frequency phase measurement in near field should be required reasonably, and the measurement errors of the intensity distributions must be as low as possible, especially the influence of far-field noise disturbance should be small enough.
2013,
25: 2511-2516.
doi: 10.3788/HPLPB20132510.2511
Abstract:
A new kind of optical lens with light weight, compact structure, good image quality, all-weather work, scurviness environment is designed based on the triturating requirement of the space camera for debris. The lens breaks through the flaw that the conventional system always has complex structure, heavy weight, large volume, and only one focal. Diffractive optical element is used to calibrate the chromatic aberration and temperature difference by its characteristics. Ge and Si are utilized to calibrate the spherochromatic aberration. The result indicates that when spatial frequency is 16 lp/mm, the MTFs are above 0.45 and 0.55 in short focal and long focal, respectively. The MTF is approaching to the diffraction limit. The maximal RMS diameters of spot diagram are 15.8 m and 7.2 m in short focal and long focal, respectively, which is less than the diameter of detecting sensor. It shows that the image quality of the lens is very good, and it calibrates the temperature difference in real circumstance of the application.
A new kind of optical lens with light weight, compact structure, good image quality, all-weather work, scurviness environment is designed based on the triturating requirement of the space camera for debris. The lens breaks through the flaw that the conventional system always has complex structure, heavy weight, large volume, and only one focal. Diffractive optical element is used to calibrate the chromatic aberration and temperature difference by its characteristics. Ge and Si are utilized to calibrate the spherochromatic aberration. The result indicates that when spatial frequency is 16 lp/mm, the MTFs are above 0.45 and 0.55 in short focal and long focal, respectively. The MTF is approaching to the diffraction limit. The maximal RMS diameters of spot diagram are 15.8 m and 7.2 m in short focal and long focal, respectively, which is less than the diameter of detecting sensor. It shows that the image quality of the lens is very good, and it calibrates the temperature difference in real circumstance of the application.
2013,
25: 2517-2520.
doi: 10.3788/HPLPB20132510.2517
Abstract:
We designed the structure of tunnel junction series stacked semiconductor lasers and grew the laser materials by molecular beam epitaxy (MBE). We fabricated the 200 m wide, 800 m cavity length laser diode chips by the process of photo-lithography, etching, Ohmic contact, cleaving, AR/HR coating and die bonding. The output power of the two-tunnel-junction device reaches 80 W under the condition of 100 ns pulsed width, 10 kHz repeat frequency, and 30 A pulsed current. The threshold current is about 0.8 A, the peak of spectrum is 905.6 nm, and the far-field divergence in the directions parallel to junction plane and perpendicular to junction plane is 7.8 and 25, respectively.
We designed the structure of tunnel junction series stacked semiconductor lasers and grew the laser materials by molecular beam epitaxy (MBE). We fabricated the 200 m wide, 800 m cavity length laser diode chips by the process of photo-lithography, etching, Ohmic contact, cleaving, AR/HR coating and die bonding. The output power of the two-tunnel-junction device reaches 80 W under the condition of 100 ns pulsed width, 10 kHz repeat frequency, and 30 A pulsed current. The threshold current is about 0.8 A, the peak of spectrum is 905.6 nm, and the far-field divergence in the directions parallel to junction plane and perpendicular to junction plane is 7.8 and 25, respectively.
2013,
25: 2521-2526.
doi: 10.3788/HPLPB20132510.2521
Abstract:
The principle of stochastic parallel gradient descent (SPGD) algorithm is introduced, and the algorithm flow is verified through simulation. Two critical factors, the stochastic perturbation and the gain coefficient, are especially analyzed. The simulation results show that there is a most appropriate interval for selecting the two factors. Only with the two factors selected in this interval, the algorithm can achieve the best convergence value. Based on the simulation results, the coherent beam combining experiments are carried out with fiber lasers, resulting in significant effect of beam combining. The experimental results prove the results of simulation above. In conclusion, the research results would improve the design of coherent beam combining experiments for high power laser in the future.
The principle of stochastic parallel gradient descent (SPGD) algorithm is introduced, and the algorithm flow is verified through simulation. Two critical factors, the stochastic perturbation and the gain coefficient, are especially analyzed. The simulation results show that there is a most appropriate interval for selecting the two factors. Only with the two factors selected in this interval, the algorithm can achieve the best convergence value. Based on the simulation results, the coherent beam combining experiments are carried out with fiber lasers, resulting in significant effect of beam combining. The experimental results prove the results of simulation above. In conclusion, the research results would improve the design of coherent beam combining experiments for high power laser in the future.
2013,
25: 2527-2530.
doi: 10.3788/HPLPB20132510.2527
Abstract:
The theory about stochastic parallel gradient descent(SPGD) algorithm and the use of SPGD algorithm for coherent beam combination are introduced. For solving the difficulty for adjusting the key parameters in SPGD algorithm, a new method of combining the hardware and software is proposed, which can online collect and analyze the experimental data and automatically adjust the key parameters in SPGD in real time. Experiments of 4 fiber-laser coherent beam combination are developed, in which different adjusting methods are compared. The results show that using new methods can efficiently achieve the value of the gain coefficient and the stochastic perturbation amplitude in SPGD algorithm. The experiments are profitable. The new method proposed in the paper is novel and effective, which can also guide the coherent beam combining experiments in the future.
The theory about stochastic parallel gradient descent(SPGD) algorithm and the use of SPGD algorithm for coherent beam combination are introduced. For solving the difficulty for adjusting the key parameters in SPGD algorithm, a new method of combining the hardware and software is proposed, which can online collect and analyze the experimental data and automatically adjust the key parameters in SPGD in real time. Experiments of 4 fiber-laser coherent beam combination are developed, in which different adjusting methods are compared. The results show that using new methods can efficiently achieve the value of the gain coefficient and the stochastic perturbation amplitude in SPGD algorithm. The experiments are profitable. The new method proposed in the paper is novel and effective, which can also guide the coherent beam combining experiments in the future.
2013,
25: 2531-2535.
doi: 10.3788/HPLPB20132510.2531
Abstract:
The rear surface defects and impurities of fused silica can absorb the laser irradiation energy strongly, resulting in the high temperature difference and thermal stress. When the thermal stress reaches the tensile strength limit, a brittle rupture will happen in the fused silica. In this study, we preload the rear surface of fused silica to weaken and counteract the damage of the thermal stress by mechanical forces. It can produce continuous changes of the pre-stress. As it is difficult to obtain the stress value in experiment, we measure the central deformation rate to the reverse surface stress distribution and simulate deformation and stress changes by ANSYS. A third harmonic generation laser damage test is utilized to the laser induced damage threshold in different pre-stress conditions. It indicates that the pre-stress 0-50 MPa can improve the laser induced damage threshold obviously, because the 0-50 MPa pre-stress can reduce and counteract the tensile stress produced from the laser irradiation. However, the pre-stress more than 50 MPa can reduce the mechanical properties by coupling effects. The pre-stress 0-50 MPa can increase the laser damage resistance effectively.
The rear surface defects and impurities of fused silica can absorb the laser irradiation energy strongly, resulting in the high temperature difference and thermal stress. When the thermal stress reaches the tensile strength limit, a brittle rupture will happen in the fused silica. In this study, we preload the rear surface of fused silica to weaken and counteract the damage of the thermal stress by mechanical forces. It can produce continuous changes of the pre-stress. As it is difficult to obtain the stress value in experiment, we measure the central deformation rate to the reverse surface stress distribution and simulate deformation and stress changes by ANSYS. A third harmonic generation laser damage test is utilized to the laser induced damage threshold in different pre-stress conditions. It indicates that the pre-stress 0-50 MPa can improve the laser induced damage threshold obviously, because the 0-50 MPa pre-stress can reduce and counteract the tensile stress produced from the laser irradiation. However, the pre-stress more than 50 MPa can reduce the mechanical properties by coupling effects. The pre-stress 0-50 MPa can increase the laser damage resistance effectively.
2013,
25: 2536-2540.
doi: 10.3788/HPLPB20132510.2536
Abstract:
There has been lacking of general simulation tools for complicated laser system in China for a long time. In order to solve this problem, we have built the component-based laser system simulation software called EasyLaser, which is based on the credible modules accumulated by many years and is very easy to use. It is composed of a general modeling and simulating platform called SciSimu and eight component libraries for simulation. It has the ability of modeling and simulating some complex processes, such as the beam propagation between the optics, the beam propagation through the atmosphere, the optical imaging, the adaptive optics correction, the recognition and tracking process, etc. The simulation ability and software feature of EasyLaser is introduced in detail in this paper. In addition, a simulation model is built by EasyLaser to analyse the correction effect of the adaptive optics system for the atmosphere turbulence.
There has been lacking of general simulation tools for complicated laser system in China for a long time. In order to solve this problem, we have built the component-based laser system simulation software called EasyLaser, which is based on the credible modules accumulated by many years and is very easy to use. It is composed of a general modeling and simulating platform called SciSimu and eight component libraries for simulation. It has the ability of modeling and simulating some complex processes, such as the beam propagation between the optics, the beam propagation through the atmosphere, the optical imaging, the adaptive optics correction, the recognition and tracking process, etc. The simulation ability and software feature of EasyLaser is introduced in detail in this paper. In addition, a simulation model is built by EasyLaser to analyse the correction effect of the adaptive optics system for the atmosphere turbulence.
2013,
25: 2541-2545.
doi: 10.3788/HPLPB20132510.2541
Abstract:
A energy balance method of preamplifier system (PSA) is given based on the PSA in SG-Ⅲ facility. The preamplifier system has realized precise control of output energy by employing the method. The results of running of the facility show that the control precision of output energy of PSA is 5.47%. Furthermore, the influence factors of output energy fluctuation of PSA are quantitatively analyzed. The analytical results show that the primary influence factor of output energy fluctuation of PSA is the instability of 1 Hz pulse energy, and the key of enhancing the stability of 1 Hz pulse energy is to control the polarized energy fluctuation of the frontend seed.
A energy balance method of preamplifier system (PSA) is given based on the PSA in SG-Ⅲ facility. The preamplifier system has realized precise control of output energy by employing the method. The results of running of the facility show that the control precision of output energy of PSA is 5.47%. Furthermore, the influence factors of output energy fluctuation of PSA are quantitatively analyzed. The analytical results show that the primary influence factor of output energy fluctuation of PSA is the instability of 1 Hz pulse energy, and the key of enhancing the stability of 1 Hz pulse energy is to control the polarized energy fluctuation of the frontend seed.
2013,
25: 2546-2550.
doi: 10.3788/HPLPB20132510.2546
Abstract:
In order to meet the cooling requirements of high-power laser devices, the influences of spray chamber pressure and nozzle bore diameter on the spray cooling performance were experimentally studied in a closed spray cooling system with R22 as refrigerant. When the inlet pressure was 0.8 MPa, the spray height was 22 mm and inlet temperature was -3 ℃, the critical heat flux (CHF) increased firstly and then decreased with the increase of spray chamber pressure form 0.2 MPa to 0.4 MPa. In addition, there existed a maximal CHF value with the change of nozzle bore diameter which indicated the spray cooling effect would deteriorate with undersize or oversize nozzle bore diameters. And the cooling surface temperature increased with the increase of spray chamber pressure. The maximal CHF of 276.1 Wcm-2 was obtained with the nozzle diameter of 0.4 mm and the spray chamber pressure of 0.34 MPa, the corresponding cooling surface temperature was 26.8 ℃ and the heat exchange coefficient was 66 640 Wm-2K-1. Bigger or smaller nozzle diameter would weaken the spray cooling performance.
In order to meet the cooling requirements of high-power laser devices, the influences of spray chamber pressure and nozzle bore diameter on the spray cooling performance were experimentally studied in a closed spray cooling system with R22 as refrigerant. When the inlet pressure was 0.8 MPa, the spray height was 22 mm and inlet temperature was -3 ℃, the critical heat flux (CHF) increased firstly and then decreased with the increase of spray chamber pressure form 0.2 MPa to 0.4 MPa. In addition, there existed a maximal CHF value with the change of nozzle bore diameter which indicated the spray cooling effect would deteriorate with undersize or oversize nozzle bore diameters. And the cooling surface temperature increased with the increase of spray chamber pressure. The maximal CHF of 276.1 Wcm-2 was obtained with the nozzle diameter of 0.4 mm and the spray chamber pressure of 0.34 MPa, the corresponding cooling surface temperature was 26.8 ℃ and the heat exchange coefficient was 66 640 Wm-2K-1. Bigger or smaller nozzle diameter would weaken the spray cooling performance.
2013,
25: 2551-2555.
doi: 10.3788/HPLPB20132510.2551
Abstract:
For heat dissipation of the high power solid state laser (HPSSL), a spray cooling system based on refrigerant cycle was designed, and its heat transfer performance was studied. Because the compressor in the refrigerant system needs lubricating, it is inevitable to mix the lubricating oil in the coolant. Lubricating oil has influence on the viscosity, surface tension of the coolant, and may produce oil film, which could strengthen or inhibit the heat transfer process of the coolant. We analyzed the influence of lubricating oil on spray cooling heat transfer performance. The experimental results show that lubricating oil increases the resistance of coolant passing through the nozzle and decreases the coolant flowrate, but as to this system, this influence could be neglected. Lubricating oil enhances the heat transfer performance of coolant, and benefits uniform distribution of the heat source temperature at low heat flux. Lubricating oil also enhances the critical heat flux and heat dissipation ability of the system, making this spray cooling system more beneficial to HPSSL heat dissipation.
For heat dissipation of the high power solid state laser (HPSSL), a spray cooling system based on refrigerant cycle was designed, and its heat transfer performance was studied. Because the compressor in the refrigerant system needs lubricating, it is inevitable to mix the lubricating oil in the coolant. Lubricating oil has influence on the viscosity, surface tension of the coolant, and may produce oil film, which could strengthen or inhibit the heat transfer process of the coolant. We analyzed the influence of lubricating oil on spray cooling heat transfer performance. The experimental results show that lubricating oil increases the resistance of coolant passing through the nozzle and decreases the coolant flowrate, but as to this system, this influence could be neglected. Lubricating oil enhances the heat transfer performance of coolant, and benefits uniform distribution of the heat source temperature at low heat flux. Lubricating oil also enhances the critical heat flux and heat dissipation ability of the system, making this spray cooling system more beneficial to HPSSL heat dissipation.
2013,
25: 2556-2560.
doi: 10.3788/HPLPB20132510.2556
Abstract:
In order to achieve high-homogeneity pumping source of semiconductor laser, the influence of microlens changes in the imaging beam integrator on the homogeneity of pumping light is researched. The relation between microlens numerical aperture and the divergence angle of the incident beam is discussed in detail. The far field distribution model of the Gaussian beam passing through the imaging beam integrator is established, in order to analyze the impact of the diffraction of microlens edge on the spot homogeneity. The upper and lower limits of clear aperture of microlens are confirmed to provide a range value for the optical design of the imaging beam integrator. Finally, the software simulation results with ZEMAX and experimental result are compared, showing that the spot of inhomogeneity 8.11% is achieved by the optimized imaging beam integrator.
In order to achieve high-homogeneity pumping source of semiconductor laser, the influence of microlens changes in the imaging beam integrator on the homogeneity of pumping light is researched. The relation between microlens numerical aperture and the divergence angle of the incident beam is discussed in detail. The far field distribution model of the Gaussian beam passing through the imaging beam integrator is established, in order to analyze the impact of the diffraction of microlens edge on the spot homogeneity. The upper and lower limits of clear aperture of microlens are confirmed to provide a range value for the optical design of the imaging beam integrator. Finally, the software simulation results with ZEMAX and experimental result are compared, showing that the spot of inhomogeneity 8.11% is achieved by the optimized imaging beam integrator.
2013,
25: 2561-2564.
doi: 10.3788/HPLPB20132510.2561
Abstract:
Many light emitting elements were periodically arranged in a high power diode laser array. Based on Talbot effect, the traditional Littrow external cavity narrow-linewidth system was improved. A Talbot external cavity was established by inserting a flat mirror with a reflection rate of 20% in the Littrow external cavity. The relative absorption coefficient was improved by 42.9% in rubidium pool absorption experiment, showing that the Talbot external cavity can improve output beam uniformity and pumping efficiency of the diode laser array.
Many light emitting elements were periodically arranged in a high power diode laser array. Based on Talbot effect, the traditional Littrow external cavity narrow-linewidth system was improved. A Talbot external cavity was established by inserting a flat mirror with a reflection rate of 20% in the Littrow external cavity. The relative absorption coefficient was improved by 42.9% in rubidium pool absorption experiment, showing that the Talbot external cavity can improve output beam uniformity and pumping efficiency of the diode laser array.
2013,
25: 2565-2570.
doi: 10.3788/HPLPB20132510.2565
Abstract:
A new cylindrical-lens spatial filter is proposed to solve the blocking pinhole problem of a spatial filter. Compared with the conventional spherical-lens spatial filter, the new filter is constituted with cylindrical lens and slit. The transmission characteristics of high power laser beam in the new cylindrical-lens spatial filter are simulated using linear transfer theory. The results show that the area of the focal spot of the new filter is bigger than that of the conventional spherical-lens spatial filter, and the power density of the focal spot is smaller, while the filtering effect and near field uniformity keep the same. The new filter can effectively inhibit the blocking effect of the filtering pinhole. At the same time, the new filter can also improve the overall price of the laser device by shortening the focal length of lens. The new cylindrical-lens spatial filter to replace the conventional spherical-lens spatial filter is feasible.
A new cylindrical-lens spatial filter is proposed to solve the blocking pinhole problem of a spatial filter. Compared with the conventional spherical-lens spatial filter, the new filter is constituted with cylindrical lens and slit. The transmission characteristics of high power laser beam in the new cylindrical-lens spatial filter are simulated using linear transfer theory. The results show that the area of the focal spot of the new filter is bigger than that of the conventional spherical-lens spatial filter, and the power density of the focal spot is smaller, while the filtering effect and near field uniformity keep the same. The new filter can effectively inhibit the blocking effect of the filtering pinhole. At the same time, the new filter can also improve the overall price of the laser device by shortening the focal length of lens. The new cylindrical-lens spatial filter to replace the conventional spherical-lens spatial filter is feasible.
2013,
25: 2571-2576.
doi: 10.3788/HPLPB20132510.2571
Abstract:
Based on the methods of vector angular spectrum and stationary phase, the analytical expressions of the TE and TM terms and the energy flux distributions of hollow Gaussian vortex beams in the far field are derived and used to analyze the phase singularities and energy flux distributions. It is shown that the far field characteristics of hollow Gaussian vortex beams depend on the control parameters. By varying the off-axis distance, both the optical vortex and the black nucleus in energy flux distributions will move. The radius of the circular edge dislocation and the dark ring position are related to the waist width, however the symmetrical spatial distribution of energy flux distributions is mainly affected by the off-axis distance.
Based on the methods of vector angular spectrum and stationary phase, the analytical expressions of the TE and TM terms and the energy flux distributions of hollow Gaussian vortex beams in the far field are derived and used to analyze the phase singularities and energy flux distributions. It is shown that the far field characteristics of hollow Gaussian vortex beams depend on the control parameters. By varying the off-axis distance, both the optical vortex and the black nucleus in energy flux distributions will move. The radius of the circular edge dislocation and the dark ring position are related to the waist width, however the symmetrical spatial distribution of energy flux distributions is mainly affected by the off-axis distance.
2013,
25: 2577-2581.
doi: 10.3788/HPLPB20132510.2577
Abstract:
The supercontinuum generation attracts more and more interest in nonlinear optical fields. The propagation of 30 fs pulse with different power and polarization state in the birefringent microstructure fibers for supercontinuum generation is studied experimentally. The experiment results show that when the injected power increases, the induced phase modulation is responsible for the initial spectral broadening, and then the fission of higher order solitons into redshifted fundamental solitons and the blueshift of dispersive wave generation attribute to the board supercontinuum generation. By rotating the input polarization of the pump femtosecond laser, besides the redshifted higher order solitons fission and blueshifted dispersive wave generation, when the polarization of the pump pulse is parallel to the long axis direction (namely the angle is 0), the center wavelength of the dispersive wave is shorter than the short-axiss (namely the angle is 90). When the polarization equals to 45, there may come forth the blueshifted cross-phase wave, and the light spot of the white-supercontinuum is the biggest in the near field distributions among the three polarization states of the pump laser.
The supercontinuum generation attracts more and more interest in nonlinear optical fields. The propagation of 30 fs pulse with different power and polarization state in the birefringent microstructure fibers for supercontinuum generation is studied experimentally. The experiment results show that when the injected power increases, the induced phase modulation is responsible for the initial spectral broadening, and then the fission of higher order solitons into redshifted fundamental solitons and the blueshift of dispersive wave generation attribute to the board supercontinuum generation. By rotating the input polarization of the pump femtosecond laser, besides the redshifted higher order solitons fission and blueshifted dispersive wave generation, when the polarization of the pump pulse is parallel to the long axis direction (namely the angle is 0), the center wavelength of the dispersive wave is shorter than the short-axiss (namely the angle is 90). When the polarization equals to 45, there may come forth the blueshifted cross-phase wave, and the light spot of the white-supercontinuum is the biggest in the near field distributions among the three polarization states of the pump laser.
2013,
25: 2582-2586.
doi: 10.3788/HPLPB20132510.2582
Abstract:
The influence of automatic brightness control on the adaptation of low-light-level TV to high light is quantitatively analyzed. First, combined with signal response characteristics, the relationship between the high light energy and the system imaging contrast is established. Then, simultaneously considering dynamic range, gain characteristic and gray level quantization, a feature quantitative model of low-light-level TV imaging after automatic brightness control operation is built. Finally, the digital simulation model of the imaging of the system which is disturbed by high light with automatic brightness control circuit, is established on the basis of the model aforementioned. Furthermore, an analysis of the effect of high light with different energy on the investigation ability of the system is deduced based on the analog output image. The theoretical analysis and experimental simulation results show that, the automatic brightness control expands the dynamic range and enhances the usability of the system, but it results in the declination of imaging quality and reconnaissance performance of the system.
The influence of automatic brightness control on the adaptation of low-light-level TV to high light is quantitatively analyzed. First, combined with signal response characteristics, the relationship between the high light energy and the system imaging contrast is established. Then, simultaneously considering dynamic range, gain characteristic and gray level quantization, a feature quantitative model of low-light-level TV imaging after automatic brightness control operation is built. Finally, the digital simulation model of the imaging of the system which is disturbed by high light with automatic brightness control circuit, is established on the basis of the model aforementioned. Furthermore, an analysis of the effect of high light with different energy on the investigation ability of the system is deduced based on the analog output image. The theoretical analysis and experimental simulation results show that, the automatic brightness control expands the dynamic range and enhances the usability of the system, but it results in the declination of imaging quality and reconnaissance performance of the system.
2013,
25: 2587-2591.
doi: 10.3788/HPLPB20132510.2587
Abstract:
The femtosecond laser ablation results of PMP foam (density of 90 mg/cm3) were analyzed. The laser pulses used for the study were 800 nm in wavelength, 50 fs in pulse duration and the repetition rate was 1000 Hz. The ablation threshold of the foam was 0.91 J/cm2 when it was shot by 100 laser pulses. The impacts of laser power, the pulse number and the numerical aperture of the focusing objective on the crater diameter were obtained. In the same femtosecond laser machining system, comparing with the ablation shape into copper foil, the important factor causing the irregular shape of the ablation region was verified that there were many different sizes and randomly distributed pores inside PMP foam. The carbonation phenomenon was observed on the edge of the ablated areas when the sample was ablated using high laser power or/and more laser pulses. Thermal effect was considered to be the causes of the carbonation. A new method based on coupling laser beam to cut thickness greater than 1 mm film-foam with femtosecond laser was proposed. Using this method, the femtosecond laser cutting thickness was greater than 1.5 mm, the angle between the cutting side wall and the laser beam optical axis might be less than 5, and the cutting surface was clean.
The femtosecond laser ablation results of PMP foam (density of 90 mg/cm3) were analyzed. The laser pulses used for the study were 800 nm in wavelength, 50 fs in pulse duration and the repetition rate was 1000 Hz. The ablation threshold of the foam was 0.91 J/cm2 when it was shot by 100 laser pulses. The impacts of laser power, the pulse number and the numerical aperture of the focusing objective on the crater diameter were obtained. In the same femtosecond laser machining system, comparing with the ablation shape into copper foil, the important factor causing the irregular shape of the ablation region was verified that there were many different sizes and randomly distributed pores inside PMP foam. The carbonation phenomenon was observed on the edge of the ablated areas when the sample was ablated using high laser power or/and more laser pulses. Thermal effect was considered to be the causes of the carbonation. A new method based on coupling laser beam to cut thickness greater than 1 mm film-foam with femtosecond laser was proposed. Using this method, the femtosecond laser cutting thickness was greater than 1.5 mm, the angle between the cutting side wall and the laser beam optical axis might be less than 5, and the cutting surface was clean.
2013,
25: 2592-2598.
doi: 10.3788/HPLPB20132510.2592
Abstract:
The influences of water vapor concentration on discharge mechanisms and discharge efficiency of atmosphere pressure plasma jet (APPJ) are studied to generate highly active cold plasma and optimize its efficiency. The discharge characteristics of APPJ with different water vapor content are studied by means of electrical measurements on voltage and current waveforms and Lissajous figures, and the optical properties are diagnosed using optical emission spectra and light-emission pictures. The main discharge parameters, such as discharge power, transported charges, electronic excitation temperature, molecular vibrational temperature and molecular rotational temperature are calculated, and the changing tendencies of them with applied voltage are studied, with the experimental results being explained by analyzing the discharge mechanism. The results show that the APPJ in Ar/H2O produces N2, Ar, O, and OH. Gas temperature changes between 525 K and 720 K, which shows that the APPJ in Ar/H2O plasma is a typical non-thermal one. With the increase of water vapor concentration, the plasma plume, light intensity and discharge power decrease, and the rotational temperature and vibrational temperature increase. Under certain discharge power, the content of OH produced reaches maximum when the water vapor content is 0.5%. Accordingly, better results can be achieved under this condition for application in surface modification of polymer materials.
The influences of water vapor concentration on discharge mechanisms and discharge efficiency of atmosphere pressure plasma jet (APPJ) are studied to generate highly active cold plasma and optimize its efficiency. The discharge characteristics of APPJ with different water vapor content are studied by means of electrical measurements on voltage and current waveforms and Lissajous figures, and the optical properties are diagnosed using optical emission spectra and light-emission pictures. The main discharge parameters, such as discharge power, transported charges, electronic excitation temperature, molecular vibrational temperature and molecular rotational temperature are calculated, and the changing tendencies of them with applied voltage are studied, with the experimental results being explained by analyzing the discharge mechanism. The results show that the APPJ in Ar/H2O produces N2, Ar, O, and OH. Gas temperature changes between 525 K and 720 K, which shows that the APPJ in Ar/H2O plasma is a typical non-thermal one. With the increase of water vapor concentration, the plasma plume, light intensity and discharge power decrease, and the rotational temperature and vibrational temperature increase. Under certain discharge power, the content of OH produced reaches maximum when the water vapor content is 0.5%. Accordingly, better results can be achieved under this condition for application in surface modification of polymer materials.
2013,
25: 2599-2603.
doi: 10.3788/HPLPB20132510.2599
Abstract:
To closely achieve diffraction-limited resolution, the surface shape of extreme ultraviolet (EUV) Schwarzschild objective requires about 1 nm (RMS value). But the mounting stress generated during the assembling process will affect the surface shape of optical components. Making quantitative calculation of mounting stress is a key point to obtain high-resolution images. On the basis of optical design and tolerance analysis, the influence of mounting stress on the surface shape of Schwarzschild objective is analyzed through the finite element model. The calculated results of the already designed structure show that, the surface shape error of primary mirror could reach to 0.7 nm (RMS value), but the influence on secondary could be ignored; the value of geometric optical transfer function (5000 lp/mm) decreased from 0.76 to 0.61 due to the surface shape error.
To closely achieve diffraction-limited resolution, the surface shape of extreme ultraviolet (EUV) Schwarzschild objective requires about 1 nm (RMS value). But the mounting stress generated during the assembling process will affect the surface shape of optical components. Making quantitative calculation of mounting stress is a key point to obtain high-resolution images. On the basis of optical design and tolerance analysis, the influence of mounting stress on the surface shape of Schwarzschild objective is analyzed through the finite element model. The calculated results of the already designed structure show that, the surface shape error of primary mirror could reach to 0.7 nm (RMS value), but the influence on secondary could be ignored; the value of geometric optical transfer function (5000 lp/mm) decreased from 0.76 to 0.61 due to the surface shape error.
2013,
25: 2604-2610.
doi: 10.3788/HPLPB20132510.2604
Abstract:
The aperture for neutron penumbral imaging is newly designed in order to reduce the difficulties of fabrication and detecting. Firstly, the source-detector and source-aperture distances are fixed on because of the neutron yield of Shenguang-Ⅲ facility. Then, base on the sharpness and isoplanaticity of the point spread function, the radii of the aperture are optimized. Finally, the resolution of the system is analysed, and the distortions induced by the aperture-fabrication error and misalignment are estimated by the simulation. According to the results, a resolution of 15 m can be satisfied, the fabrication error should be limited to a maximum of 0.1, the precision of alignment should be better than 60 m, the aperture rotation should be within 0.35 mrad, and the source-aperture distance error should be less than 1 mm.
The aperture for neutron penumbral imaging is newly designed in order to reduce the difficulties of fabrication and detecting. Firstly, the source-detector and source-aperture distances are fixed on because of the neutron yield of Shenguang-Ⅲ facility. Then, base on the sharpness and isoplanaticity of the point spread function, the radii of the aperture are optimized. Finally, the resolution of the system is analysed, and the distortions induced by the aperture-fabrication error and misalignment are estimated by the simulation. According to the results, a resolution of 15 m can be satisfied, the fabrication error should be limited to a maximum of 0.1, the precision of alignment should be better than 60 m, the aperture rotation should be within 0.35 mrad, and the source-aperture distance error should be less than 1 mm.
2013,
25: 2611-2615.
doi: 10.3788/HPLPB20132510.2611
Abstract:
A novel hard X-ray bent crystal spectrometer, composed of a cylindrically bent crystal, a specula CsI(Tl) scintillator, an image intensifier and a CCD, were proposed, which had the quantitative measurement ability. The details of a quantitative calibration method using X-ray tube and Si(Li) detector was explained. The absolute efficiency of the spectrometer on 17 keV and 19 keV was calibrated using the method. The results indicated that the efficiency on both energy was coherent in dimension. Several issues which might ameliorate the calibration method were discussed.
A novel hard X-ray bent crystal spectrometer, composed of a cylindrically bent crystal, a specula CsI(Tl) scintillator, an image intensifier and a CCD, were proposed, which had the quantitative measurement ability. The details of a quantitative calibration method using X-ray tube and Si(Li) detector was explained. The absolute efficiency of the spectrometer on 17 keV and 19 keV was calibrated using the method. The results indicated that the efficiency on both energy was coherent in dimension. Several issues which might ameliorate the calibration method were discussed.
2013,
25: 2616-2620.
doi: 10.3788/HPLPB20132510.2616
Abstract:
With the development of the ICF experiment, a streak camera with a wider dynamic range is required. A double focusing lens streak tube with wide dynamic range is designed to satisfy this requirement. Technical parameters of the tube are obtained by optimizing the electrode sizes and voltages values. The deflection sensitivity is 39 mm/kV. The spatial resolution is better than 30 lp/mm in the middle of the photocathode and better than 10 lp/mm at the edge. The time resolution is about 10 ps. The effective length of the photocathode is 30 mm, the magnification is 1.3. Some measures are taken to improve dynamic range, including enhancing the on-axis potential and decreasing the electrode length. As a result, the minimum on-axis potential reaches 5 kV and the flying time of electrons from photocathode to screen is only 6.62 ns. A tube is made based on the designed size. The primary parameters are obtained by testing the tube. The actual voltage values applied to electrodes are almost the same as the designed values. The tested deflection sensitivity is 40 mm/kV and the magnification is 1.35, which both consist with the designed parameters.
With the development of the ICF experiment, a streak camera with a wider dynamic range is required. A double focusing lens streak tube with wide dynamic range is designed to satisfy this requirement. Technical parameters of the tube are obtained by optimizing the electrode sizes and voltages values. The deflection sensitivity is 39 mm/kV. The spatial resolution is better than 30 lp/mm in the middle of the photocathode and better than 10 lp/mm at the edge. The time resolution is about 10 ps. The effective length of the photocathode is 30 mm, the magnification is 1.3. Some measures are taken to improve dynamic range, including enhancing the on-axis potential and decreasing the electrode length. As a result, the minimum on-axis potential reaches 5 kV and the flying time of electrons from photocathode to screen is only 6.62 ns. A tube is made based on the designed size. The primary parameters are obtained by testing the tube. The actual voltage values applied to electrodes are almost the same as the designed values. The tested deflection sensitivity is 40 mm/kV and the magnification is 1.35, which both consist with the designed parameters.
2013,
25: 2621-2626.
doi: 10.3788/HPLPB20132510.2621
Abstract:
Activated N-doped carbon aerogel (N-ACA) is synthesized by the sol-gel polycondensation of resorcinol with formaldehyde using the melamine as nitrogen source, and then the carbon derivative being activated in CO2 flow. The surface morphology and porous structure are analyzed using scanning electron microscopy (SEM) and N2 adsorption at 77 K. The contained nitrogen of surface and monolith is tested by X-ray photoelectron spectroscopy (XPS) and elemental analysis. The electrochemical performances of N-dope carbon aerogels as electrodes are confirmed using constant-current charge-discharge test (GV), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). It reveals that the rich porous structure and the chemical state of nitrogen functionalities have crucial effect on the electrochemical performance of the electric double-layer capacitors. The appropriate CO2 activation can increase the number of micropores and mesopores as well as the specific surface area (4082 m2g-1).Furthermore, the presence of amount of pyrrolic nitrogen is reinforced in the electron donor capacity. The specific capacitance of N-ACA electrode is up to 211.9 Fg-1 and retains about 98% after 500 charge-discharge cycles.
Activated N-doped carbon aerogel (N-ACA) is synthesized by the sol-gel polycondensation of resorcinol with formaldehyde using the melamine as nitrogen source, and then the carbon derivative being activated in CO2 flow. The surface morphology and porous structure are analyzed using scanning electron microscopy (SEM) and N2 adsorption at 77 K. The contained nitrogen of surface and monolith is tested by X-ray photoelectron spectroscopy (XPS) and elemental analysis. The electrochemical performances of N-dope carbon aerogels as electrodes are confirmed using constant-current charge-discharge test (GV), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). It reveals that the rich porous structure and the chemical state of nitrogen functionalities have crucial effect on the electrochemical performance of the electric double-layer capacitors. The appropriate CO2 activation can increase the number of micropores and mesopores as well as the specific surface area (4082 m2g-1).Furthermore, the presence of amount of pyrrolic nitrogen is reinforced in the electron donor capacity. The specific capacitance of N-ACA electrode is up to 211.9 Fg-1 and retains about 98% after 500 charge-discharge cycles.
2013,
25: 2627-2630.
doi: 10.3788/HPLPB20132510.2627
Abstract:
The DC magnetron sputtering was explored to fabricate Au thin films with thicknesses of 5, 10, 15, 20 nm on the silica substrates. These films were annealed in high purity nitrogen ambient at 800℃ and Au particles of different diameters were obtained on the silica substrates. The novel Au photocathodes were prepared by depositing a layer of 50 nm Au film on the silica substrates with Au particles. SEM showed that Au photocathodes with particles ranging from 300-800 nm were obtained. The photoemission characteristics of Au photocathodes under ultraviolet light between 190-360 nm were obtained, which indicated that the novel Au photocathodes with nano-particles emitted 10 times more photoelectrons than the plane Au photocathodes. This result is explained by semi-classical three-step model of photoemission.
The DC magnetron sputtering was explored to fabricate Au thin films with thicknesses of 5, 10, 15, 20 nm on the silica substrates. These films were annealed in high purity nitrogen ambient at 800℃ and Au particles of different diameters were obtained on the silica substrates. The novel Au photocathodes were prepared by depositing a layer of 50 nm Au film on the silica substrates with Au particles. SEM showed that Au photocathodes with particles ranging from 300-800 nm were obtained. The photoemission characteristics of Au photocathodes under ultraviolet light between 190-360 nm were obtained, which indicated that the novel Au photocathodes with nano-particles emitted 10 times more photoelectrons than the plane Au photocathodes. This result is explained by semi-classical three-step model of photoemission.
2013,
25: 2631-2635.
doi: 10.3788/HPLPB20132510.2631
Abstract:
The plasma size has important influence on the power of the extreme ultraviolet source at the intermediate focus (IF point) and the design of the illumination system for a capillary discharge extreme ultraviolet source. The collection efficiency was calculated under different lengths of the plasma theoretically. Moreover, the spectra of the Xe plasma under different lengths of the plasma were obtained by a Rowland spectrometer. By combining the theoretical and experimental results with the design of the collectors in this system, the 13.5 nm (2% bandwidth) emissions at the IF point were calculated under different lengths of the plasma. The results show that the optimal power at the IF point and the optimal size of the plasma can be obtained when the length of the plasma is 3-6 mm.
The plasma size has important influence on the power of the extreme ultraviolet source at the intermediate focus (IF point) and the design of the illumination system for a capillary discharge extreme ultraviolet source. The collection efficiency was calculated under different lengths of the plasma theoretically. Moreover, the spectra of the Xe plasma under different lengths of the plasma were obtained by a Rowland spectrometer. By combining the theoretical and experimental results with the design of the collectors in this system, the 13.5 nm (2% bandwidth) emissions at the IF point were calculated under different lengths of the plasma. The results show that the optimal power at the IF point and the optimal size of the plasma can be obtained when the length of the plasma is 3-6 mm.
2013,
25: 2636-2642.
doi: 10.3788/HPLPB20132510.2636
Abstract:
The relativistic magnetron is a crossed-field device and plays an important role in the high power microwave technology and radar system. Recently, researchers realized mode switching in relativistic magnetron between neighbour modes as well as different longitudinal operation modes in the same modes with several hundred kilowatts RF input signal. Unfortunately, the RF input power is assumed to already power into the relativistic magnetron cavity, though in reality not considering such work. A novel RF input technology is proposed in this article, using a rod antenna to couple the input RF signal from the input sector waveguide into the relativistic magnetron cavity. In the PIC simulation with UNIPIC code, by adjusting the antenna position and the antenna configuration, the coupling efficiency between the antenna and input sector waveguide can be optimized. This new method can be used in power and energy input for mode switching, and the simulation results can be used as references for RF signal input in future experiment.
The relativistic magnetron is a crossed-field device and plays an important role in the high power microwave technology and radar system. Recently, researchers realized mode switching in relativistic magnetron between neighbour modes as well as different longitudinal operation modes in the same modes with several hundred kilowatts RF input signal. Unfortunately, the RF input power is assumed to already power into the relativistic magnetron cavity, though in reality not considering such work. A novel RF input technology is proposed in this article, using a rod antenna to couple the input RF signal from the input sector waveguide into the relativistic magnetron cavity. In the PIC simulation with UNIPIC code, by adjusting the antenna position and the antenna configuration, the coupling efficiency between the antenna and input sector waveguide can be optimized. This new method can be used in power and energy input for mode switching, and the simulation results can be used as references for RF signal input in future experiment.
2013,
25: 2643-2647.
doi: 10.3788/HPLPB20132510.2643
Abstract:
The finite-difference method is used to analyze the dispersion characteristics of two-dimensional photonic band gap (PBG) structures formed by triangular arrays of metal posts. The global band gaps for TE modes are derived. The method of designing PBG structures with specific eigen-frequency is obtained. It is shown that for the convenience of coupling the power out of the PBG cavity, the ratio of post radius to lattice constant should be as small as possible. The results also prove that it is possible to design a gyrotron with PBG cavities analogous to conventional cylindrical cavities.
The finite-difference method is used to analyze the dispersion characteristics of two-dimensional photonic band gap (PBG) structures formed by triangular arrays of metal posts. The global band gaps for TE modes are derived. The method of designing PBG structures with specific eigen-frequency is obtained. It is shown that for the convenience of coupling the power out of the PBG cavity, the ratio of post radius to lattice constant should be as small as possible. The results also prove that it is possible to design a gyrotron with PBG cavities analogous to conventional cylindrical cavities.
2013,
25: 2648-2652.
doi: 10.3788/HPLPB20132510.2648
Abstract:
A design of waveguide slot-array antenna for high power applications is introduced. The slots are on the narrow side of waveguide. By achieving uniform radiation of each slot, it is possible to expand the array; besides, it is possible to realize beam scanning in the azimuth direction by adjusting the broad wall dimension of waveguide. The slot antenna has high power capacity while it is working in traveling wave state without the enhancement of electric field and in a vacuum environment.
A design of waveguide slot-array antenna for high power applications is introduced. The slots are on the narrow side of waveguide. By achieving uniform radiation of each slot, it is possible to expand the array; besides, it is possible to realize beam scanning in the azimuth direction by adjusting the broad wall dimension of waveguide. The slot antenna has high power capacity while it is working in traveling wave state without the enhancement of electric field and in a vacuum environment.
2013,
25: 2653-2658.
doi: 10.3788/HPLPB20132510.2653
Abstract:
Using a 1D3V PIC code programmed by authors, the physical course of multipactor discharge suppressing on dielectric surface with different external magnetic field patterns is studied numerically. The secondary electron number, average electron energy, electron density, electron trajectories, transition time, static electric field and deposited power on dielectric surface are given in simulations. The numerical results could be concluded as follows: The mechanism of different external magnetic field loading patterns is not the same. For the normal direction external magnetic field loading, the rotation caused by external magnetic field disturbs microwave electric field accelerating electron course in order to decrease the impact energy which could suppress the multipactor discharge. For the parallel direction external magnetic field loading, the electrons are pushed out of dielectric surface in half microwave period which could not induce multipactor discharge, and the electrons are pushed in dielectric surface in the other half microwave period which could decrease the impact energy for suppressing the multipactor discharge. The resonant magnetic field condition is also discussed which could cause electron rotation radius and energy increasing continuously. The multipactor discharge suppressing effect could be improved by increasing the value of magnetic field for every external magnetic field loading pattern. It is easy to achieve loading but with higher value of magnetic field for normal direction external magnetic field. On the contrary, it is hard to achieve loading but with lower value of magnetic field for parallel direction external magnetic field.
Using a 1D3V PIC code programmed by authors, the physical course of multipactor discharge suppressing on dielectric surface with different external magnetic field patterns is studied numerically. The secondary electron number, average electron energy, electron density, electron trajectories, transition time, static electric field and deposited power on dielectric surface are given in simulations. The numerical results could be concluded as follows: The mechanism of different external magnetic field loading patterns is not the same. For the normal direction external magnetic field loading, the rotation caused by external magnetic field disturbs microwave electric field accelerating electron course in order to decrease the impact energy which could suppress the multipactor discharge. For the parallel direction external magnetic field loading, the electrons are pushed out of dielectric surface in half microwave period which could not induce multipactor discharge, and the electrons are pushed in dielectric surface in the other half microwave period which could decrease the impact energy for suppressing the multipactor discharge. The resonant magnetic field condition is also discussed which could cause electron rotation radius and energy increasing continuously. The multipactor discharge suppressing effect could be improved by increasing the value of magnetic field for every external magnetic field loading pattern. It is easy to achieve loading but with higher value of magnetic field for normal direction external magnetic field. On the contrary, it is hard to achieve loading but with lower value of magnetic field for parallel direction external magnetic field.
2013,
25: 2659-2662.
doi: 10.3788/HPLPB20132510.2659
Abstract:
A novel coaxial directional coupler was designed for L-band high power microwave radiation field measurement. It could incredibly decrease the size of the coupler to use two different kinds of transmission lines and coupling aperture with continuous variation width along the propagation direction. The aperture is determined by infinitesimal method, small hole coupling formulas and numerical full wave simulation optimization. Based on the simulation results, the structure of the coupler is optimized and fabricated, and the measurement results indicate that, the size of the directional coupler is 150 mm46 mm55 mm, and during 1-2 GHz, the coupling is 47 dB, the directivity is more than 17 dB.
A novel coaxial directional coupler was designed for L-band high power microwave radiation field measurement. It could incredibly decrease the size of the coupler to use two different kinds of transmission lines and coupling aperture with continuous variation width along the propagation direction. The aperture is determined by infinitesimal method, small hole coupling formulas and numerical full wave simulation optimization. Based on the simulation results, the structure of the coupler is optimized and fabricated, and the measurement results indicate that, the size of the directional coupler is 150 mm46 mm55 mm, and during 1-2 GHz, the coupling is 47 dB, the directivity is more than 17 dB.
2013,
25: 2663-2666.
doi: 10.3788/HPLPB20132510.2663
Abstract:
This paper presents a quasi-optical mode converter which can convert the output mode of gyrotrons and other high-power microwave oscillators into quasi-Gaussian beam, aiming to achieve transverse output of quasi-Gaussian beam TEM00 mode. First, we analyze mode propagation in the waveguide and the working mechanism of the Vlasov launcher. Then the radiation fields are calculated using vector diffraction theory. At last a quasi-optical mode converter is designed to convert the 94 GHz, TE62 mode millimeter wave into quasi-Gaussian beam with programming method. The results prove that quasi-Gaussian mode can be obtained at the output window with a simple Vlasov launcher and two mirrors, and the power transmission efficiency of the quasi-optical mode converter reaches to 87.5%.
This paper presents a quasi-optical mode converter which can convert the output mode of gyrotrons and other high-power microwave oscillators into quasi-Gaussian beam, aiming to achieve transverse output of quasi-Gaussian beam TEM00 mode. First, we analyze mode propagation in the waveguide and the working mechanism of the Vlasov launcher. Then the radiation fields are calculated using vector diffraction theory. At last a quasi-optical mode converter is designed to convert the 94 GHz, TE62 mode millimeter wave into quasi-Gaussian beam with programming method. The results prove that quasi-Gaussian mode can be obtained at the output window with a simple Vlasov launcher and two mirrors, and the power transmission efficiency of the quasi-optical mode converter reaches to 87.5%.
2013,
25: 2667-2670.
doi: 10.3788/HPLPB20132510.2667
Abstract:
For heavy-ion radiotherapy, HIRFL-CSR (Heavy Ion Research Facility in Lanzhou-Cooler Storage Ring) needs a long term uniform ion beam extraction from HIRFL-CSR main ring to high energy beam transport line to meet the requirement of heavy-ion radiotherapys ion beam. Slow extraction control system uses the synchronous signal of HIRFL-CSR control systems timing system to realize process control. When the synchronous event data of HIRFL-CSR control systems timing system trigger controlling and changing data (frequency value, tune value, voltage value), the waveform generator will generate waveform by frequency value, tune value and voltage value, and will amplify the generated waveform by power amplifier to electrostatic deflector to achieve RF-KO slow extraction. The synchronous event receiver of slow extraction system is designed by using FPGA and optical fiber interface to keep high transmission speed and anti-jamming. HIRFL-CSRs running for heavy-ion radiotherapy and ten thousand seconds long period slow extraction experiments show that slow extraction control system is workable and can meet the requirement of heavy-ion radiotherapys ion beam.
For heavy-ion radiotherapy, HIRFL-CSR (Heavy Ion Research Facility in Lanzhou-Cooler Storage Ring) needs a long term uniform ion beam extraction from HIRFL-CSR main ring to high energy beam transport line to meet the requirement of heavy-ion radiotherapys ion beam. Slow extraction control system uses the synchronous signal of HIRFL-CSR control systems timing system to realize process control. When the synchronous event data of HIRFL-CSR control systems timing system trigger controlling and changing data (frequency value, tune value, voltage value), the waveform generator will generate waveform by frequency value, tune value and voltage value, and will amplify the generated waveform by power amplifier to electrostatic deflector to achieve RF-KO slow extraction. The synchronous event receiver of slow extraction system is designed by using FPGA and optical fiber interface to keep high transmission speed and anti-jamming. HIRFL-CSRs running for heavy-ion radiotherapy and ten thousand seconds long period slow extraction experiments show that slow extraction control system is workable and can meet the requirement of heavy-ion radiotherapys ion beam.
2013,
25: 2671-2674.
doi: 10.3788/HPLPB20132510.2671
Abstract:
Based on the prototype of rapid cycling synchrotron of China spallation neutron source(CSNS/RCS) RF system, this paper presents a scheme on beam loading compensation in high-intensity proton synchrotron. The scheme includes adaptive beam feedforward, direct RF feedback, pre-detuning of cavity and dynamic tuning of both cavity and amplifier, and their realization by an integrated digital low-level RF control system without lowering the quality factor of the cavity and changing its mechanical structure.
Based on the prototype of rapid cycling synchrotron of China spallation neutron source(CSNS/RCS) RF system, this paper presents a scheme on beam loading compensation in high-intensity proton synchrotron. The scheme includes adaptive beam feedforward, direct RF feedback, pre-detuning of cavity and dynamic tuning of both cavity and amplifier, and their realization by an integrated digital low-level RF control system without lowering the quality factor of the cavity and changing its mechanical structure.
2013,
25: 2675-2681.
doi: 10.3788/HPLPB20132510.2675
Abstract:
Proton beam window (PBW) is a critical component of the China accelerator-driven system (C-ADS), which will isolate the accelerator vacuum from the target. Scattering effect induced by material of the PBW and the cooling medium is the most important factor causing the beam loss out of the target. Very high energy deposition and irradiation load of the PBW make the thermal hydraulic research especially indispensable. For beam window with multiple pipe structure, calculation results show that lost particles can be controlled within 1% when the beam window is located at 1.5 m from the target. The stress induced by heat load and cooling medium as well as pressure difference over the PBW can be controlled within permissible stress of present selected material. Primary parameters of the PBW of C-ADS are also given through analysis and discussion.
Proton beam window (PBW) is a critical component of the China accelerator-driven system (C-ADS), which will isolate the accelerator vacuum from the target. Scattering effect induced by material of the PBW and the cooling medium is the most important factor causing the beam loss out of the target. Very high energy deposition and irradiation load of the PBW make the thermal hydraulic research especially indispensable. For beam window with multiple pipe structure, calculation results show that lost particles can be controlled within 1% when the beam window is located at 1.5 m from the target. The stress induced by heat load and cooling medium as well as pressure difference over the PBW can be controlled within permissible stress of present selected material. Primary parameters of the PBW of C-ADS are also given through analysis and discussion.
2013,
25: 2682-2686.
doi: 10.3788/HPLPB20132510.2682
Abstract:
The laser-induced breakdown spectroscopy was applied to the measurement of pulverized coal flow. The interaction between laser and sample stream, as well as the effects of different focal depth on the plasma excitation characteristics was analyzed. On the self-built two-phase flow experimental bench, the coal particles flow was ablated with laser in the atmospheric environment, under 1, 0.5, 0, -0.5 and -1 mm depth of focus, and the spectrometer was used to collect the plasma signal. Under certain conditions of laser energy and angle of received light, the changes of the plasma temperature, the electron density and the spectra of C, Si and Al with laser focal depth were studied. The results show that the laser focal depth has obvious impacts on the plasma temperature, electron density and elemental spectral intensity. The overall variation of the three parameters are consistency, and the most optimum point is at 0 mm, followed by 1.0, 0.5, -0.5 mm and the worst point is at -1 mm.
The laser-induced breakdown spectroscopy was applied to the measurement of pulverized coal flow. The interaction between laser and sample stream, as well as the effects of different focal depth on the plasma excitation characteristics was analyzed. On the self-built two-phase flow experimental bench, the coal particles flow was ablated with laser in the atmospheric environment, under 1, 0.5, 0, -0.5 and -1 mm depth of focus, and the spectrometer was used to collect the plasma signal. Under certain conditions of laser energy and angle of received light, the changes of the plasma temperature, the electron density and the spectra of C, Si and Al with laser focal depth were studied. The results show that the laser focal depth has obvious impacts on the plasma temperature, electron density and elemental spectral intensity. The overall variation of the three parameters are consistency, and the most optimum point is at 0 mm, followed by 1.0, 0.5, -0.5 mm and the worst point is at -1 mm.
2013,
25: 2687-2692.
doi: 10.3788/HPLPB20132510.2687
Abstract:
Considering the working principle of the neutral beam injection system (NBI) for experimental advanced superconducting tokamak (EAST), the ion dump using calorimetric method with cooling tube inside was proposed to absorb the un-neutralized ions and measure the loaded energy. According to the physical characteristics of EAST NBI, together with the engineering limitation and requirement for measurement and cooling method, the detailed design decision of ion dump was given after the design performance indexes were analyzed, especially the dump board, including the material, design and arrangement of the cooling way inside. The proposed ion dump of V-shape with the cooling tube inside in this study was constructed and tested in the test bed of EAST NBI, and the feasibility of ion dump was proved by the experiment results under the working condition of 4 MW power and 10 s pulse length. This study lays a solid foundation to realize the experiment target of high power with high parameters and steady state for EAST NBI in the next step.
Considering the working principle of the neutral beam injection system (NBI) for experimental advanced superconducting tokamak (EAST), the ion dump using calorimetric method with cooling tube inside was proposed to absorb the un-neutralized ions and measure the loaded energy. According to the physical characteristics of EAST NBI, together with the engineering limitation and requirement for measurement and cooling method, the detailed design decision of ion dump was given after the design performance indexes were analyzed, especially the dump board, including the material, design and arrangement of the cooling way inside. The proposed ion dump of V-shape with the cooling tube inside in this study was constructed and tested in the test bed of EAST NBI, and the feasibility of ion dump was proved by the experiment results under the working condition of 4 MW power and 10 s pulse length. This study lays a solid foundation to realize the experiment target of high power with high parameters and steady state for EAST NBI in the next step.
2013,
25: 2693-2698.
doi: 10.3788/HPLPB20132510.2693
Abstract:
In cone-beam CT imaging system, it is difficult to directly measure the geometry parameters. In this paper, a geometry calibration method for rotation translation trajectory is proposed. Intrinsic parameters are solved from the relationship built on geometry parameter of the system and projection trajectory of calibration object. Parameters of rotation axis are extrapolated from the unified intrinsic parameter, and geometry parameters of the idle trajectory are acquired too. The calibration geometry can be analytically determined using explicit formulae, it can avoid getting into local optimum in iterative way. Simulation experiments are carried out on misaligned geometry, experiment results indicate that geometry artifacts due to misaligned geometry are effectively depressed by the proposed method, and the image quality is enhanced.
In cone-beam CT imaging system, it is difficult to directly measure the geometry parameters. In this paper, a geometry calibration method for rotation translation trajectory is proposed. Intrinsic parameters are solved from the relationship built on geometry parameter of the system and projection trajectory of calibration object. Parameters of rotation axis are extrapolated from the unified intrinsic parameter, and geometry parameters of the idle trajectory are acquired too. The calibration geometry can be analytically determined using explicit formulae, it can avoid getting into local optimum in iterative way. Simulation experiments are carried out on misaligned geometry, experiment results indicate that geometry artifacts due to misaligned geometry are effectively depressed by the proposed method, and the image quality is enhanced.
2013,
25: 2699-2704.
doi: 10.3788/HPLPB20132510.2699
Abstract:
An online measurement system for radiation effects on synchronous dynamic random access memory (SDRAM) is developed on the basis of the analysis of the main failure phenomenon, which can test the function, refresh period and power supply current. The results of an experiment on SDRAM for total ionizing dose effect (TID) show that the TID can cause the decrease in data retention time, the increase in power supply current and the functional failure. For the samples MT48LC8M32B2, its functional failure is caused by the peripheral control circuits, rather than the memory unit upset. Data retention time keeps decreasing with the increase of the total dose, but this is not the directive reason for the functional failure of SDRAM.
An online measurement system for radiation effects on synchronous dynamic random access memory (SDRAM) is developed on the basis of the analysis of the main failure phenomenon, which can test the function, refresh period and power supply current. The results of an experiment on SDRAM for total ionizing dose effect (TID) show that the TID can cause the decrease in data retention time, the increase in power supply current and the functional failure. For the samples MT48LC8M32B2, its functional failure is caused by the peripheral control circuits, rather than the memory unit upset. Data retention time keeps decreasing with the increase of the total dose, but this is not the directive reason for the functional failure of SDRAM.
2013,
25: 2705-2710.
doi: 10.3788/HPLPB20132510.2705
Abstract:
Single event effect experimental study on 90 nm and 65 nm DDR SRAM were carried out, single event upset (SEU) cross section was discussed as a function of several parameters such as feature size, test pattern, incidence angle, supply voltage. Key influence factors and effect rule were analyzed. Feasibility of the current test method was discussed. Results indicate that, SEU cross section reduces as technologies scale down; the influence of test pattern and power supply on SEU cross section is small; tilt angle increases SEU cross section due to multiple upset increasement. The applicability of cosine tilt test method is correlative to ion species and linear energy transfer (LET) values.
Single event effect experimental study on 90 nm and 65 nm DDR SRAM were carried out, single event upset (SEU) cross section was discussed as a function of several parameters such as feature size, test pattern, incidence angle, supply voltage. Key influence factors and effect rule were analyzed. Feasibility of the current test method was discussed. Results indicate that, SEU cross section reduces as technologies scale down; the influence of test pattern and power supply on SEU cross section is small; tilt angle increases SEU cross section due to multiple upset increasement. The applicability of cosine tilt test method is correlative to ion species and linear energy transfer (LET) values.
2013,
25: 2711-2716.
doi: 10.3788/HPLPB20132510.2711
Abstract:
With SiC diode and neutron conversion material 6LiF, neutron detector based on SiC was fabricated. The alpha-particle and thermal neutron response of neutron detector based on SiC were studied by 241Am-alpha source and critical assembly, respectively. Excellent signals from the neutron detector to both alpha-particles and thermal neutrons have been observed. The neutron detector can be applied to particle intensity measurement. But because of the thin epitaxial layer, the detector can not be used for 5.48 MeV alpha-particle energy measurement. With different reactor power, the double peaks of alpha particles and 3H particles in the spectrum were obviously observed. A small amount of energy from gamma-ray was deposited in SiC neutron detector, which could be discriminated by pulse height discriminator. Count rate of SiC neutron detector was linear with critical assembly power, and which has a linearity of 0.999 97. After all, for SiC diode, it can be used for energy measurement by decreasing the thickness of Scotty contact metal and increasing the depth and qualities of epitaxial layer.
With SiC diode and neutron conversion material 6LiF, neutron detector based on SiC was fabricated. The alpha-particle and thermal neutron response of neutron detector based on SiC were studied by 241Am-alpha source and critical assembly, respectively. Excellent signals from the neutron detector to both alpha-particles and thermal neutrons have been observed. The neutron detector can be applied to particle intensity measurement. But because of the thin epitaxial layer, the detector can not be used for 5.48 MeV alpha-particle energy measurement. With different reactor power, the double peaks of alpha particles and 3H particles in the spectrum were obviously observed. A small amount of energy from gamma-ray was deposited in SiC neutron detector, which could be discriminated by pulse height discriminator. Count rate of SiC neutron detector was linear with critical assembly power, and which has a linearity of 0.999 97. After all, for SiC diode, it can be used for energy measurement by decreasing the thickness of Scotty contact metal and increasing the depth and qualities of epitaxial layer.
2013,
25: 2717-2722.
doi: 10.3788/HPLPB20132510.2717
Abstract:
The microwave circulator is expected to be integrated with low temperature co-fired ceramics (LTCC) technique by multilayer chip structure design. In this paper, the X band microstrip ferrite circulator is designed with the three-dimensional electromagnetic simulation method. The whole substrate consists of gyrotropic stack layers, which provides different saturation magnetization. The results show that the stack number and saturation magnetization of the stack layers exhibit considerable effect on the return loss and reverse isolation for the circulator. It suggests to be correlated with the input equivalent circuit parameters for the circulator, which are affected by the interface and varied saturation magnetization of the stack layers in multilayer chip structure. High return loss, high reverse isolation and low insertion loss can be obtained with the optimized design. However, it is found that the bandwidth of the circulator is unaffected by the stack number and saturation magnetization of the stack layers, which is difficult to be improved with the optimized design.
The microwave circulator is expected to be integrated with low temperature co-fired ceramics (LTCC) technique by multilayer chip structure design. In this paper, the X band microstrip ferrite circulator is designed with the three-dimensional electromagnetic simulation method. The whole substrate consists of gyrotropic stack layers, which provides different saturation magnetization. The results show that the stack number and saturation magnetization of the stack layers exhibit considerable effect on the return loss and reverse isolation for the circulator. It suggests to be correlated with the input equivalent circuit parameters for the circulator, which are affected by the interface and varied saturation magnetization of the stack layers in multilayer chip structure. High return loss, high reverse isolation and low insertion loss can be obtained with the optimized design. However, it is found that the bandwidth of the circulator is unaffected by the stack number and saturation magnetization of the stack layers, which is difficult to be improved with the optimized design.
2013,
25: 2723-2728.
doi: 10.3788/HPLPB20132510.2723
Abstract:
Wear-resistant composite coatings were fabricated on substrate of a titanium alloy Ti6Al4V by laser metal deposition (LMD) process using Cr2C3, WC and Ti powders in order to enhance the tribological properties of Ti6Al4V. The microstructure of the coatings was characterized and the coating microhardness was tested. And their wear resistance was evaluated under room-temperature dry-sliding wear test conditions. The results show that the two kinds composite coatings have fine microstructure consisting of in-situ TiC particles and the unmelted WC particles uniformly distributed in the matrix and are metallurgically bonded to the titanium substrate. The coatings exhibit excellent wear resistance due to the rapidly solidified fine microstructure and the presence of a large amount of in-situ TiC and WC phase. The coating with TiC reinforced phase has better hardness gradient and slightly lower wear resistance than the coating with WC particles.
Wear-resistant composite coatings were fabricated on substrate of a titanium alloy Ti6Al4V by laser metal deposition (LMD) process using Cr2C3, WC and Ti powders in order to enhance the tribological properties of Ti6Al4V. The microstructure of the coatings was characterized and the coating microhardness was tested. And their wear resistance was evaluated under room-temperature dry-sliding wear test conditions. The results show that the two kinds composite coatings have fine microstructure consisting of in-situ TiC particles and the unmelted WC particles uniformly distributed in the matrix and are metallurgically bonded to the titanium substrate. The coatings exhibit excellent wear resistance due to the rapidly solidified fine microstructure and the presence of a large amount of in-situ TiC and WC phase. The coating with TiC reinforced phase has better hardness gradient and slightly lower wear resistance than the coating with WC particles.
Experimental condition optimization of laser-induced breakdown spectroscopy based on sequential test
2013,
25: 2729-2733.
doi: 10.3788/HPLPB20132510.2729
Abstract:
The Nd: YAG pulsed laser with 1064 nm wavelength was used as a light source to produce laser-induced plasma on the surface of the aluminum alloy, and the spectral signal was detected with three-grating spectrometer and width controlled ICCD. The intensity and the signal to background ratio of two characteristic lines of Al Ⅰ 394.40 nm and Al Ⅰ 396.15 nm were analyzed. It is shown that the delay of the ICCD detection, the width of the ICCD gate and the energy of laser pulse have great influences on the spectral signals and the signal to background ratio, and the variation of the width of the ICCD gate leads to the fluctuation of the signal to background ratio. By optimizing the parameters, the optimum conditions were determined, and high spectral intensity and signal to background ratio were obtained under low laser energy. The experimental results lay a foundation for the qualitative and quantitative detection of the components of the aluminum alloy.
The Nd: YAG pulsed laser with 1064 nm wavelength was used as a light source to produce laser-induced plasma on the surface of the aluminum alloy, and the spectral signal was detected with three-grating spectrometer and width controlled ICCD. The intensity and the signal to background ratio of two characteristic lines of Al Ⅰ 394.40 nm and Al Ⅰ 396.15 nm were analyzed. It is shown that the delay of the ICCD detection, the width of the ICCD gate and the energy of laser pulse have great influences on the spectral signals and the signal to background ratio, and the variation of the width of the ICCD gate leads to the fluctuation of the signal to background ratio. By optimizing the parameters, the optimum conditions were determined, and high spectral intensity and signal to background ratio were obtained under low laser energy. The experimental results lay a foundation for the qualitative and quantitative detection of the components of the aluminum alloy.
2013,
25: 2734-2738.
doi: 10.3788/HPLPB20132510.2734
Abstract:
The detector quantum efficiency (DQE) is used to describe the propagation of the noise in the imaging system. According to the cascade theory, the DQE of the high-energy gamma camera depends on the gain of the scintillator and the CCD, and the absorbed energy deposition in the scintillator. In this paper, the Monte Carlo code MCNP is employed to simulate the distribution of the energy deposition for X-ray through different scintillators. The DQE of the high-energy gamma camera for different scintillator with different thickness is calculated and analysed. From the simulation, it can be seen that the DQE is correlative with the density and the atomic number of the scintillator. The DQEs of the LuAP and LSO are much bigger than other scintillator with the same thickness. The method presented in this paper can be used to the design of the high-energy gamma camera.
The detector quantum efficiency (DQE) is used to describe the propagation of the noise in the imaging system. According to the cascade theory, the DQE of the high-energy gamma camera depends on the gain of the scintillator and the CCD, and the absorbed energy deposition in the scintillator. In this paper, the Monte Carlo code MCNP is employed to simulate the distribution of the energy deposition for X-ray through different scintillators. The DQE of the high-energy gamma camera for different scintillator with different thickness is calculated and analysed. From the simulation, it can be seen that the DQE is correlative with the density and the atomic number of the scintillator. The DQEs of the LuAP and LSO are much bigger than other scintillator with the same thickness. The method presented in this paper can be used to the design of the high-energy gamma camera.
2013,
25: 2739-2741.
doi: 10.3788/HPLPB20132510.2739
Abstract:
A thermionic cathode with a mixed LaB6 and TaC emission layer was investigated. Emission properties of cathodes with LaB6 to TaC weight ratios of 1∶1, 2∶1, and 3∶1 were studied and compared. The work function of the mixed LaB6 cathode was found to be similar to that of polycrystalline LaB6 cathodes. Stable electron emission with a current density of about 30 A/cm2 was achieved with cathode recipe of 3∶1. The cathode can be applied to vacuum electronic devices and dynamic vacuum electron-beam equipments where large electron current density and extremely large area cathodes are demanded.
A thermionic cathode with a mixed LaB6 and TaC emission layer was investigated. Emission properties of cathodes with LaB6 to TaC weight ratios of 1∶1, 2∶1, and 3∶1 were studied and compared. The work function of the mixed LaB6 cathode was found to be similar to that of polycrystalline LaB6 cathodes. Stable electron emission with a current density of about 30 A/cm2 was achieved with cathode recipe of 3∶1. The cathode can be applied to vacuum electronic devices and dynamic vacuum electron-beam equipments where large electron current density and extremely large area cathodes are demanded.
2013,
25: 2742-2746.
doi: 10.3788/HPLPB20132510.2742
Abstract:
A high-voltage pulsed power supply for testing the character of ZnO varistor, with adjustable pulse width, repetition frequency and running time, and most 80 kV rectangle wave-output voltage, is developed. Rectangle-wave voltage pulse is produced by pulse forming line, pulse transformer and adjustable load. Two spark gap switches work under the control of the program which generates sequence pulses by a high speed I/O data card. All control and sample signals are transmitted by optical fiber in order to reduce the influence of electromagnetic interference on the whole control system. A user-friend human-machine interface has been built on LabVIEW platform. The experimental result shows that the automatic control system runs stably, reliably, and has a strong anti-interference ability. The output voltage of the supply power is over 80 kV, pulse width over 25 s, rise time less than 0.7 s. The output voltage and pulse width can be adjusted within the anticipant range. The output current is adjustable from 0 up to 40 A in ZnO varistor testing.
A high-voltage pulsed power supply for testing the character of ZnO varistor, with adjustable pulse width, repetition frequency and running time, and most 80 kV rectangle wave-output voltage, is developed. Rectangle-wave voltage pulse is produced by pulse forming line, pulse transformer and adjustable load. Two spark gap switches work under the control of the program which generates sequence pulses by a high speed I/O data card. All control and sample signals are transmitted by optical fiber in order to reduce the influence of electromagnetic interference on the whole control system. A user-friend human-machine interface has been built on LabVIEW platform. The experimental result shows that the automatic control system runs stably, reliably, and has a strong anti-interference ability. The output voltage of the supply power is over 80 kV, pulse width over 25 s, rise time less than 0.7 s. The output voltage and pulse width can be adjusted within the anticipant range. The output current is adjustable from 0 up to 40 A in ZnO varistor testing.
2013,
25: 2747-2752.
doi: 10.3788/HPLPB20132510.2747
Abstract:
Under the assumption that the guide rail is a semi-infinite solid conductor and main armature surface wear is the wear based on melting, and according to the solid contact heat conduction principle, the armature and the rail temperature distribution equations are deduced, and the calculation method of average wear rate in armatures is put forward. The influences of average wear rate on driving current, the matching of armature and guide materials and the contact area of the armature are studied. The average wear rate calculation results agree well with Stefani and Parkers experimental results, which verifies the validity of the method.
Under the assumption that the guide rail is a semi-infinite solid conductor and main armature surface wear is the wear based on melting, and according to the solid contact heat conduction principle, the armature and the rail temperature distribution equations are deduced, and the calculation method of average wear rate in armatures is put forward. The influences of average wear rate on driving current, the matching of armature and guide materials and the contact area of the armature are studied. The average wear rate calculation results agree well with Stefani and Parkers experimental results, which verifies the validity of the method.
2013,
25: 2753-2756.
doi: 10.3788/HPLPB20132510.2753
Abstract:
The non-parametric method is conventionally used to evaluate data in lot acceptance testing (LAT) of transient ionizing radiation. But the evaluation results are very conservative and will lead to an increase of the trial cost. The ordering method in the sample space was introduced and applied to compute the lower confidence limit of survival probability based on zero-failure data and was compared with the non-parametric method both theoretically and via a practical LAT on QG-Ⅰ. It is concluded that the ordering method can not only improve the lower confidence limit of survival probability but also expand the scope of dose rate corresponding to the lower confidence limit. Results indicate that the ordering method improves data utilization and makes the evaluation less conservative and can save the trial cost.
The non-parametric method is conventionally used to evaluate data in lot acceptance testing (LAT) of transient ionizing radiation. But the evaluation results are very conservative and will lead to an increase of the trial cost. The ordering method in the sample space was introduced and applied to compute the lower confidence limit of survival probability based on zero-failure data and was compared with the non-parametric method both theoretically and via a practical LAT on QG-Ⅰ. It is concluded that the ordering method can not only improve the lower confidence limit of survival probability but also expand the scope of dose rate corresponding to the lower confidence limit. Results indicate that the ordering method improves data utilization and makes the evaluation less conservative and can save the trial cost.
2013,
25: 2757-2762.
doi: 10.3788/HPLPB20132510.2757
Abstract:
The differential capacitive voltage divider and inductive voltage divider were designed for voltage measurement of magnetically-insulated transmission line (MITL) on a 10-stage fast linear transformer driver (LTD) system. The dividers were calibrated in-situ with a 12 kV pulser. The voltage of MITL was measured with the two voltage dividers. The experimental results show that, the differential capacitive voltage divider signal is susceptible to MITL sheath electrons. But when the electrons are highly insulated, the capacitive divider signal could reflect the history of MITL voltage. There is oscillation in the waveform of inductive divider, which is believed to be resulted from the parasitic capacitance and inductance according to circuit simulations. However, the real voltage waveform could be reconstructed with post-processing according to frequency response analysis.
The differential capacitive voltage divider and inductive voltage divider were designed for voltage measurement of magnetically-insulated transmission line (MITL) on a 10-stage fast linear transformer driver (LTD) system. The dividers were calibrated in-situ with a 12 kV pulser. The voltage of MITL was measured with the two voltage dividers. The experimental results show that, the differential capacitive voltage divider signal is susceptible to MITL sheath electrons. But when the electrons are highly insulated, the capacitive divider signal could reflect the history of MITL voltage. There is oscillation in the waveform of inductive divider, which is believed to be resulted from the parasitic capacitance and inductance according to circuit simulations. However, the real voltage waveform could be reconstructed with post-processing according to frequency response analysis.
2013,
25: 2763-2766.
doi: 10.3788/HPLPB20132510.2763
Abstract:
The inductances of the primary and second coil are important parameters of Tesla transformer. Some elementary research is carried out on the magnetic circuit of Tesla transformer with open circuit magnetic core, including the calculation on magnetic force lines and the magnetic flux density distribution all over the Tesla transformer magnetic circuit. The result shows that, in the magnetic core regions, the magnetic force lines mainly concentrate inside magnetic cores, and in the region between inner and outer magnetic cores, the magnetic force lines mainly distribute between the primary/second coil ends and the magnetic core ends. Practically, the magnetic leakage of Tesla transformer (Generally, the length of Tesla transformers primary and secondary coil is half of the length of magnetic core.) is comparatively small. Given the assumption that there is no magnetic leakage, we estimate the primary and secondary coil inductances of Tesla transformer. The error of the estimation is less than 15% compared to the measurement, which indicates that the arithmetic introduced in this paper is a convenient and advantageous method to solve the problem of design and parameters estimation of Tesla transformer.
The inductances of the primary and second coil are important parameters of Tesla transformer. Some elementary research is carried out on the magnetic circuit of Tesla transformer with open circuit magnetic core, including the calculation on magnetic force lines and the magnetic flux density distribution all over the Tesla transformer magnetic circuit. The result shows that, in the magnetic core regions, the magnetic force lines mainly concentrate inside magnetic cores, and in the region between inner and outer magnetic cores, the magnetic force lines mainly distribute between the primary/second coil ends and the magnetic core ends. Practically, the magnetic leakage of Tesla transformer (Generally, the length of Tesla transformers primary and secondary coil is half of the length of magnetic core.) is comparatively small. Given the assumption that there is no magnetic leakage, we estimate the primary and secondary coil inductances of Tesla transformer. The error of the estimation is less than 15% compared to the measurement, which indicates that the arithmetic introduced in this paper is a convenient and advantageous method to solve the problem of design and parameters estimation of Tesla transformer.
2013,
25: 2767-2771.
doi: 10.3788/HPLPB20132510.2767
Abstract:
No whole-stack flashover has been observed under the working voltage of about 2 MV in the PTS vacuum insulator stack, because of the uniform voltage distributions on different insulator rings, the effects of azimuthal transit-time and multi-stage structure. In this paper, two typical abnormal voltage waveforms are interpreted to be caused by the different flashover locations. The experimental results preliminarily validate the rules of transmission, attenuation and composition of transient electromagnetic waves in different mediums, caused by flashover. The stochastic occurrence of flashover presents a certain extent systemic discrepancy in two modules along with the increasing of experiment time, due to deposits accumulation on the surface of the insulator rings.
No whole-stack flashover has been observed under the working voltage of about 2 MV in the PTS vacuum insulator stack, because of the uniform voltage distributions on different insulator rings, the effects of azimuthal transit-time and multi-stage structure. In this paper, two typical abnormal voltage waveforms are interpreted to be caused by the different flashover locations. The experimental results preliminarily validate the rules of transmission, attenuation and composition of transient electromagnetic waves in different mediums, caused by flashover. The stochastic occurrence of flashover presents a certain extent systemic discrepancy in two modules along with the increasing of experiment time, due to deposits accumulation on the surface of the insulator rings.
2013,
25: 2772-2776.
doi: 10.3788/HPLPB20132510.2772
Abstract:
A multi-gap rail switch is introduced with its configuration and self-breakdown experiments. The streamer theory gives a Raether criterion which is used to estimate if the gap can be broken down. An equation about self-breakdown voltage is obtained from the criterion. When the switch has high gas pressure, there is a visible difference between experimental data and empirical relation. Breakdown voltage nonlinearly increases with increasing pressure, and by analyzing the experimental condition and data, its reason may be corona from electrode surface. Because of special geometry of the switch, the corona can not only make the electric field uniform but also decrease the distance of A-K gap under high voltage and high gas pressure.
A multi-gap rail switch is introduced with its configuration and self-breakdown experiments. The streamer theory gives a Raether criterion which is used to estimate if the gap can be broken down. An equation about self-breakdown voltage is obtained from the criterion. When the switch has high gas pressure, there is a visible difference between experimental data and empirical relation. Breakdown voltage nonlinearly increases with increasing pressure, and by analyzing the experimental condition and data, its reason may be corona from electrode surface. Because of special geometry of the switch, the corona can not only make the electric field uniform but also decrease the distance of A-K gap under high voltage and high gas pressure.
