Email alert
RSS2013 Vol. 25, No. S0
Recommend Articles
Display Method:
2013,
25: 1-4.
Abstract:
We apply the ray tracing method to design of high-energy-laser calorimeter. With the backward scattering problem of the calorimeter with conical cavity, we use the ray tracing method for energy simulation, and the simulation results compared with the theoretical results verify the feasibility of the method. Moreover, this method can be applied to design of actual high-energy-laser calorimeter.
We apply the ray tracing method to design of high-energy-laser calorimeter. With the backward scattering problem of the calorimeter with conical cavity, we use the ray tracing method for energy simulation, and the simulation results compared with the theoretical results verify the feasibility of the method. Moreover, this method can be applied to design of actual high-energy-laser calorimeter.
2013,
25: 5-8.
Abstract:
The analytic expression of the intensity of any polarizing direction versus the phase difference in polarization coherent beam combining is deduced. The validity of the expression is proved by experiment. The coherent beam combining(CBC) experiment based on polarization phase discrimination is designed to verify the feasibility of CBC based on polarization phase discrimination. The phase of two laser beam is locked using gradient descent algorithm and a stable power output is acquired. The advantage of this technology and the requirement of lasers are analyzed. A scalable architecture of full aperture CBC based on polarization phase discrimination which can be proportionally amplified is proposed. The quick degradation of the bandwidth of the stochastic parallel gradient descent algorithm(SPGD) as the increase of the CBS beams is solved by multiple parallel phase detection and modulation.
The analytic expression of the intensity of any polarizing direction versus the phase difference in polarization coherent beam combining is deduced. The validity of the expression is proved by experiment. The coherent beam combining(CBC) experiment based on polarization phase discrimination is designed to verify the feasibility of CBC based on polarization phase discrimination. The phase of two laser beam is locked using gradient descent algorithm and a stable power output is acquired. The advantage of this technology and the requirement of lasers are analyzed. A scalable architecture of full aperture CBC based on polarization phase discrimination which can be proportionally amplified is proposed. The quick degradation of the bandwidth of the stochastic parallel gradient descent algorithm(SPGD) as the increase of the CBS beams is solved by multiple parallel phase detection and modulation.
2013,
25: 9-12.
Abstract:
The diffraction effect of the laser emission system is simulated using the format of 2D Fourier transform of the Fresnel diffraction integral formula. The method of fast Fourier transform(FFT) is used to calculate diffraction integral formula, and the condition under which the secondary phase factor meets the sampling theory is discussed. Different methods applied to calculating the diffractive field of different transmission distance are proposed. The transmission effect of intensity modulation for input laser is analyzed.
The diffraction effect of the laser emission system is simulated using the format of 2D Fourier transform of the Fresnel diffraction integral formula. The method of fast Fourier transform(FFT) is used to calculate diffraction integral formula, and the condition under which the secondary phase factor meets the sampling theory is discussed. Different methods applied to calculating the diffractive field of different transmission distance are proposed. The transmission effect of intensity modulation for input laser is analyzed.
2013,
25: 13-18.
Abstract:
According to the experiment of validation and optimization, the design of thin film's weak absorption testing set-up is finished for quick development of high energy laser, which can achieve the aims of high testing precision, large aperture, various wavelengths, various angles and reflective measurement. From the measurement results of system function and optics weak absorption, it can be judged that the system's precision is 10-6 .
According to the experiment of validation and optimization, the design of thin film's weak absorption testing set-up is finished for quick development of high energy laser, which can achieve the aims of high testing precision, large aperture, various wavelengths, various angles and reflective measurement. From the measurement results of system function and optics weak absorption, it can be judged that the system's precision is 10-6 .
2013,
25: 19-23.
Abstract:
VMM(vector-matrix-multiply) method was widely used for wave-front reconstruction in Shack-Hartmann wave-front sensor. Taking advantage of great number of calculations, VMM can give accurate enough result for most of cases, but it can not work properly in scenes which have strict requirement of frequency in time or special domain. In this paper, wave-front is intended to be reconstructed by FTR(Fourier transform reconstruction) method. A common software routine was designed and implemented based on Shack-Hartmann sensor model and FTR algorithms. With the help of these codes, the time analysis of FTR was obtained by software tests. Two kinds of data set were used for the study of accuracy performance, one was ideal slopes derived for known wave-front, the other was slopes corrupted by random noise from actual experiment. Then wave-fronts reconstructed by VMM and FTR were compared and analyzed. Results demonstrate that FTR algorithm has the capability to yield unbiased reconstructions, and shares better time performance than VMM method. Due to extra steps to maintain periodical property of slope data, the wave-front difference between FTR and VMM appears more apparently in edge area. The study and analysis make the limited factors clear, and will guide the implement of FTR in Shack-Hartmann wave-front sensor and supply clues for the improvement in future works.
VMM(vector-matrix-multiply) method was widely used for wave-front reconstruction in Shack-Hartmann wave-front sensor. Taking advantage of great number of calculations, VMM can give accurate enough result for most of cases, but it can not work properly in scenes which have strict requirement of frequency in time or special domain. In this paper, wave-front is intended to be reconstructed by FTR(Fourier transform reconstruction) method. A common software routine was designed and implemented based on Shack-Hartmann sensor model and FTR algorithms. With the help of these codes, the time analysis of FTR was obtained by software tests. Two kinds of data set were used for the study of accuracy performance, one was ideal slopes derived for known wave-front, the other was slopes corrupted by random noise from actual experiment. Then wave-fronts reconstructed by VMM and FTR were compared and analyzed. Results demonstrate that FTR algorithm has the capability to yield unbiased reconstructions, and shares better time performance than VMM method. Due to extra steps to maintain periodical property of slope data, the wave-front difference between FTR and VMM appears more apparently in edge area. The study and analysis make the limited factors clear, and will guide the implement of FTR in Shack-Hartmann wave-front sensor and supply clues for the improvement in future works.
2013,
25: 24-28.
Abstract:
In the premise of stabilized tracking for the dynamic target, the centerline extracted is very important to the high accuracy of target location and real-time pose decision, because it is the major judging for target location. According to the Hessian matrixs geometric sense in differential geometry and the 2D feature of target in image, the method of centerline extracted based on eigen decomposition of Hessian matrix was proposed. On the basis of targets segmentation, the Hessian matrix with gray of target in image can be constructed by Euclidean transformation. And then the initial gather of center points can be gained by the eigen decomposition of Hessian matrix. Finally the centerline can be extracted after the bad points were rejected with RANSAC algorithm. In order to prove the availability of this method, with the evaluation index being set the simulation experiment was developed. The results show this method has obvious stability and veracity.
In the premise of stabilized tracking for the dynamic target, the centerline extracted is very important to the high accuracy of target location and real-time pose decision, because it is the major judging for target location. According to the Hessian matrixs geometric sense in differential geometry and the 2D feature of target in image, the method of centerline extracted based on eigen decomposition of Hessian matrix was proposed. On the basis of targets segmentation, the Hessian matrix with gray of target in image can be constructed by Euclidean transformation. And then the initial gather of center points can be gained by the eigen decomposition of Hessian matrix. Finally the centerline can be extracted after the bad points were rejected with RANSAC algorithm. In order to prove the availability of this method, with the evaluation index being set the simulation experiment was developed. The results show this method has obvious stability and veracity.
2013,
25: 29-32.
Abstract:
A kind of separated COIL resonant cavity using the I-shaped structure, a supporting system and wire-rope isolators is designed. Through simulation, the structure of the supporting system is optimized with the target of increasing its first natural frequency and maximizing its material utilization ratio. Its performance of vibration supression and stabilization is assessed by analysing how the large damping ratio of wire cable isolator influences the performance of the vibration supression and stabilization of the system. The result of the analysis reveals that the wire rope isolators enhance the performance of the vibration supression and stabilization.
A kind of separated COIL resonant cavity using the I-shaped structure, a supporting system and wire-rope isolators is designed. Through simulation, the structure of the supporting system is optimized with the target of increasing its first natural frequency and maximizing its material utilization ratio. Its performance of vibration supression and stabilization is assessed by analysing how the large damping ratio of wire cable isolator influences the performance of the vibration supression and stabilization of the system. The result of the analysis reveals that the wire rope isolators enhance the performance of the vibration supression and stabilization.
2013,
25: 33-38.
Abstract:
A wavelet domain Wiener filtering method is proposed for denoising of cone-beam dental CT images. The db4 wavelet is used to decompose the CT image, and the Wiener filtering is implemented in each scale of wavelet coefficients, while the parameters of local mean and noise variance estimation are adjusted based on region statistical characteristics in each scale of wavelet coefficients. New wavelet coefficients are used for the reconstruction of the denoised image, and the denoised CT image is obtained. The results of computer simulation and the cone-beam dental CT actual data prove that this method raises the reconstruction images signal-to-noise ratio, suppresses image noise effectively, and then improves the image visual effect obviously.
A wavelet domain Wiener filtering method is proposed for denoising of cone-beam dental CT images. The db4 wavelet is used to decompose the CT image, and the Wiener filtering is implemented in each scale of wavelet coefficients, while the parameters of local mean and noise variance estimation are adjusted based on region statistical characteristics in each scale of wavelet coefficients. New wavelet coefficients are used for the reconstruction of the denoised image, and the denoised CT image is obtained. The results of computer simulation and the cone-beam dental CT actual data prove that this method raises the reconstruction images signal-to-noise ratio, suppresses image noise effectively, and then improves the image visual effect obviously.
2013,
25: 39-45.
Abstract:
The courses of the energy transfer from electricity to the Nd:glass disk were numerically analyzed, such as electricity-light conversion of Xenon flash lamp, cavity transformation, the absorbing of pump-light converting to the laser-energy level and decay. The theoretical and experimental results show that the boosting of energy-storage efficiency of the flash-lamp pumped Nd:glass amplifier should be achieved by means of improving the material, design and fabrication of the amplifier and its power conditioning system.
The courses of the energy transfer from electricity to the Nd:glass disk were numerically analyzed, such as electricity-light conversion of Xenon flash lamp, cavity transformation, the absorbing of pump-light converting to the laser-energy level and decay. The theoretical and experimental results show that the boosting of energy-storage efficiency of the flash-lamp pumped Nd:glass amplifier should be achieved by means of improving the material, design and fabrication of the amplifier and its power conditioning system.
2013,
25: 46-50.
Abstract:
By researching on the character and application method of EPOLL mechanism, a magnanimous network data processing model based on EPOLL mechanism in Linux is advanced. The problems about multithread synchronization and data access mechanism in multithread situation are chiefly discussed, and material actualizing steps of the model are given on Linux/QT platform. On application occasion of large-scale network links, the model can provide fast response and good data security.
By researching on the character and application method of EPOLL mechanism, a magnanimous network data processing model based on EPOLL mechanism in Linux is advanced. The problems about multithread synchronization and data access mechanism in multithread situation are chiefly discussed, and material actualizing steps of the model are given on Linux/QT platform. On application occasion of large-scale network links, the model can provide fast response and good data security.
2013,
25: 51-54.
Abstract:
Sky background luminance is very important in imaging and optical information transition in space. The existing sky luminance simulation codes, such as Modtran cant be suitable for different climate and global location. Therefore, we developed a sky luminance measurement device and obtained a lot of experimental data. By analyzing these data, we found that in homogeneous sky background, the sky spectral luminance decreases with the increase of solar angle in general, but when the angle between observation direction and ground plane is less than 30, the luminance increases with the decreasing solar angle. In fine and cloudless sky background, the sky luminance is concentrated at short-wave band, while in cloudy background there is obvious redshift of the luminance spectrum.
Sky background luminance is very important in imaging and optical information transition in space. The existing sky luminance simulation codes, such as Modtran cant be suitable for different climate and global location. Therefore, we developed a sky luminance measurement device and obtained a lot of experimental data. By analyzing these data, we found that in homogeneous sky background, the sky spectral luminance decreases with the increase of solar angle in general, but when the angle between observation direction and ground plane is less than 30, the luminance increases with the decreasing solar angle. In fine and cloudless sky background, the sky luminance is concentrated at short-wave band, while in cloudy background there is obvious redshift of the luminance spectrum.
2013,
25: 55-58.
Abstract:
This article briefly describes the various components of the airborne light detection and ranging system, and analyzes error factors of the system. According to the Mianyang-Chengdu-Leshan inter-city railway station line engineering data of different base stations, we have differential treatment of the airborne GPS (global positioning system). Detailed comparative analysis of the forward/reverse separation mean value/distribution and photo positional accuracy of the calculated flight trajectories is performed. Finally we arrive at the ground base station layout scheme to improve data accuracy.
This article briefly describes the various components of the airborne light detection and ranging system, and analyzes error factors of the system. According to the Mianyang-Chengdu-Leshan inter-city railway station line engineering data of different base stations, we have differential treatment of the airborne GPS (global positioning system). Detailed comparative analysis of the forward/reverse separation mean value/distribution and photo positional accuracy of the calculated flight trajectories is performed. Finally we arrive at the ground base station layout scheme to improve data accuracy.
2013,
25: 59-62.
Abstract:
The optimization design is important to structural design. The structural optimization design of an optical platforms table surface was obtained in which the surface tables mechanical capability was used as the topology optimization constraining parameter, and one type of model was got. The optimization process is not perfect and some farther work must be carried on.
The optimization design is important to structural design. The structural optimization design of an optical platforms table surface was obtained in which the surface tables mechanical capability was used as the topology optimization constraining parameter, and one type of model was got. The optimization process is not perfect and some farther work must be carried on.
2013,
25: 63-66.
Abstract:
The base of optical cavity is the major structure of a chemical laser. The dynamic characteristics analysis of the base is very important. Aimed at the practical base, modal simulation is done by two boundary conditions, the influential factors of dynamic characteristics are analyzed from the results. The first six modal parameters are obtained from the modal experiment. By comparing with the simulation, the shape characteristics are analyzed, the boundary condition of the bottom and the connection of corrugated tubes are also evaluated. The results are of benefit to the design and improvement of the chemical laser system. The results show that the connect stiffness is very low, and the constraint of corrugated tube does not change modal rules.
The base of optical cavity is the major structure of a chemical laser. The dynamic characteristics analysis of the base is very important. Aimed at the practical base, modal simulation is done by two boundary conditions, the influential factors of dynamic characteristics are analyzed from the results. The first six modal parameters are obtained from the modal experiment. By comparing with the simulation, the shape characteristics are analyzed, the boundary condition of the bottom and the connection of corrugated tubes are also evaluated. The results are of benefit to the design and improvement of the chemical laser system. The results show that the connect stiffness is very low, and the constraint of corrugated tube does not change modal rules.
2013,
25: 67-70.
Abstract:
Using wavefront reconfiguration and corrector is one of the effective approaches in improving the beam quality control of the high energy laser system. A general architecture of embedded wavefront process and control system, as well as the theoretic analysis of the reconfiguring and controlling algorithm, is given in this paper to achieve the measurement, reconfiguration and correction of the wavefront aberrance. Then, designs of high-speed wavefront process and driver control modules are discussed in detail. Based on the principle of full digital design, the mass data processing and command parameter generating can be accomplished on the hardware platform of digital circuit. By using the method of embedded adaptive control, the system can work in the unattended operation mode to control the beam quality of the high energy laser system.
Using wavefront reconfiguration and corrector is one of the effective approaches in improving the beam quality control of the high energy laser system. A general architecture of embedded wavefront process and control system, as well as the theoretic analysis of the reconfiguring and controlling algorithm, is given in this paper to achieve the measurement, reconfiguration and correction of the wavefront aberrance. Then, designs of high-speed wavefront process and driver control modules are discussed in detail. Based on the principle of full digital design, the mass data processing and command parameter generating can be accomplished on the hardware platform of digital circuit. By using the method of embedded adaptive control, the system can work in the unattended operation mode to control the beam quality of the high energy laser system.
2013,
25: 71-76.
Abstract:
The free modes of an optical platform were analyzed with finite element method, and then the modal testing was accomplished in actual operating conditions. The first order frequencies in the vertical and horizontal directions of the optical platform were obtained by identifying the modal parameters of the platform structure, which were 126.77 and 361.42 Hz respectively. The stiffness of the platform was verified to meet the requirements for the optical experiments.
The free modes of an optical platform were analyzed with finite element method, and then the modal testing was accomplished in actual operating conditions. The first order frequencies in the vertical and horizontal directions of the optical platform were obtained by identifying the modal parameters of the platform structure, which were 126.77 and 361.42 Hz respectively. The stiffness of the platform was verified to meet the requirements for the optical experiments.
Application of thermal effect of infrared light to forming uniform DD layers in spherical cryotarget
2013,
25: 77-80.
Abstract:
Based on the request of the solid fuel in inertial confinement fusion (ICF) capsule and the thermal effect of infrared (IR) light, the IR lights function of changing the spatial distribution and micro-structure of solid deuterium is studied. It is found that with the special IR light (3140 nm, 100 W), the micro-structure of solid deuterium is changed from polycrystal to monocrystal, the solid deuterium is redistributed and becomes more uniform. The exhibition of optical image is that a distinct bright band appears. By analysis of the bright band, the RMS surface roughness of the solid deuterium is calculated.
Based on the request of the solid fuel in inertial confinement fusion (ICF) capsule and the thermal effect of infrared (IR) light, the IR lights function of changing the spatial distribution and micro-structure of solid deuterium is studied. It is found that with the special IR light (3140 nm, 100 W), the micro-structure of solid deuterium is changed from polycrystal to monocrystal, the solid deuterium is redistributed and becomes more uniform. The exhibition of optical image is that a distinct bright band appears. By analysis of the bright band, the RMS surface roughness of the solid deuterium is calculated.
2013,
25: 81-86.
Abstract:
The design method of hardware-in-the-loop simulation platform for measurement and control system is introduced. The system hardware is implemented by using computer and PCI interface card, and the electric characteristics of control interface are simulated veritably. The control function of correlative sub-system is simulated according to veritable communication principles including principles of shared-memory communication and CAN communication, etc. The simulation platform is successfully applied to measurement and control system, and the quality of the system is improved.
The design method of hardware-in-the-loop simulation platform for measurement and control system is introduced. The system hardware is implemented by using computer and PCI interface card, and the electric characteristics of control interface are simulated veritably. The control function of correlative sub-system is simulated according to veritable communication principles including principles of shared-memory communication and CAN communication, etc. The simulation platform is successfully applied to measurement and control system, and the quality of the system is improved.
2013,
25: 87-90.
Abstract:
Software testing is one of the most important means to ensure quality of software. The design of test cases is the key of software testing. This paper describes several methods of black-box testing technologies and how to skillfully apply black-box testing technologies to the command and control subsystem software testing. It is shown that in this system software testing, the application of these black-box testing technologies significantly increases the efficiency of the test case designing with good performance. The application value can be popularized to other projects.
Software testing is one of the most important means to ensure quality of software. The design of test cases is the key of software testing. This paper describes several methods of black-box testing technologies and how to skillfully apply black-box testing technologies to the command and control subsystem software testing. It is shown that in this system software testing, the application of these black-box testing technologies significantly increases the efficiency of the test case designing with good performance. The application value can be popularized to other projects.
2013,
25: 91-95.
Abstract:
The function and relationship of all parts of MVC mode are introduced. According to operation requirement peculiarity of command and control system, a certain relationship model is advanced based on MVC mode. To meet the development requirement of command and control system software in a certain experiment, the software architecture is designed. In Linux environment, the command and control software is actualized based on QT development platform.
The function and relationship of all parts of MVC mode are introduced. According to operation requirement peculiarity of command and control system, a certain relationship model is advanced based on MVC mode. To meet the development requirement of command and control system software in a certain experiment, the software architecture is designed. In Linux environment, the command and control software is actualized based on QT development platform.
2013,
25: 96-100.
Abstract:
Many fire control systems nowadays need real-time tracking and pointing to targets. In their design, demonstration and analysis, it is often necessary to estimate the angular velocity, angular acceleration and their variation law to provide basis for designing tracking and pointing system. However, systematic exposition for these issues is hard to find. Therefore, theoretical deductions are strictly made for often-involved long-range space targets to obtain quantitive formulae about angular velocity, angular acceleration as well as their maximum values. The deductions specially aim at ground-level tracking systems. Results of theoretical calculations with these formulae are compared with some real-measured data from a target. Conformity of the two types of results proves all the formulae are correct. The obtained formulae are also fit for short-range targets, which can be seen from the procedure of deduction.
Many fire control systems nowadays need real-time tracking and pointing to targets. In their design, demonstration and analysis, it is often necessary to estimate the angular velocity, angular acceleration and their variation law to provide basis for designing tracking and pointing system. However, systematic exposition for these issues is hard to find. Therefore, theoretical deductions are strictly made for often-involved long-range space targets to obtain quantitive formulae about angular velocity, angular acceleration as well as their maximum values. The deductions specially aim at ground-level tracking systems. Results of theoretical calculations with these formulae are compared with some real-measured data from a target. Conformity of the two types of results proves all the formulae are correct. The obtained formulae are also fit for short-range targets, which can be seen from the procedure of deduction.
2013,
25: 101-105.
Abstract:
The investigation and project for navigating, surveying and control of aviation based on GoogleEarth(GE) is introduced. Lots of problems in navigation probe and control with simple aerostat are solved. The veracity is improved, meanwhile the difficulty in fly is depressed by reducing airmans flight control. By using the map resource of GE, the source and cost are least by using.
The investigation and project for navigating, surveying and control of aviation based on GoogleEarth(GE) is introduced. Lots of problems in navigation probe and control with simple aerostat are solved. The veracity is improved, meanwhile the difficulty in fly is depressed by reducing airmans flight control. By using the map resource of GE, the source and cost are least by using.
2013,
25: 106-110.
Abstract:
Different geometrical characteristics are common in the modelling and analysis of microwave structure, the hybrid modeling method based on solid element and shell element is very effective, because the element and node number will decrease by the method. Aimed at the degree of freedom (DOF) matching problem, the implement and application of multipoint constraint (MPC) method is researched, the problem is analyzed with the feed structure analysis, and its accuracy is validated. The results show that the MPC method is very accurate, but building a model in the load area will lead to error.
Different geometrical characteristics are common in the modelling and analysis of microwave structure, the hybrid modeling method based on solid element and shell element is very effective, because the element and node number will decrease by the method. Aimed at the degree of freedom (DOF) matching problem, the implement and application of multipoint constraint (MPC) method is researched, the problem is analyzed with the feed structure analysis, and its accuracy is validated. The results show that the MPC method is very accurate, but building a model in the load area will lead to error.
2013,
25: 111-114.
Abstract:
The air breakdown caused by high power microwave pulse was studied theoretically and simulated numerically. The electron density expressions for single pulse and repetition-frequency pulse were deduced. The thresholds of air breakdown by high power microwave pulse under different atmospheric pressures, pulse widths and repetition frequencies were given. The experimental system of air breakdown by high power microwave pulse was designed and the experimental study was carried out. The result of experiment was mainly in accordance with the theoretical calculation.
The air breakdown caused by high power microwave pulse was studied theoretically and simulated numerically. The electron density expressions for single pulse and repetition-frequency pulse were deduced. The thresholds of air breakdown by high power microwave pulse under different atmospheric pressures, pulse widths and repetition frequencies were given. The experimental system of air breakdown by high power microwave pulse was designed and the experimental study was carried out. The result of experiment was mainly in accordance with the theoretical calculation.
2013,
25: 115-118.
Abstract:
A Denisov launcher for transforming TE6,2 mode to Gaussian-like mode is proposed to be employed in 3 mm Gyrotron. Based on the mode coupling theory, the design method of the Denisov launcher is shown. By adopting developed mathematical programme, the TE6,2 Denisov launcher is studied using the concrete parameters of the 3 mm whispering gallery mode gyrotron, with its length of 52 mm. It is verified by electromagnetic field simulation that, the launchers wall current of the cut edges decreases to 10% of the central focused current. The cold test result of Denisov mode converter is better than that of Vlasov mode converter.
A Denisov launcher for transforming TE6,2 mode to Gaussian-like mode is proposed to be employed in 3 mm Gyrotron. Based on the mode coupling theory, the design method of the Denisov launcher is shown. By adopting developed mathematical programme, the TE6,2 Denisov launcher is studied using the concrete parameters of the 3 mm whispering gallery mode gyrotron, with its length of 52 mm. It is verified by electromagnetic field simulation that, the launchers wall current of the cut edges decreases to 10% of the central focused current. The cold test result of Denisov mode converter is better than that of Vlasov mode converter.
2013,
25: 119-123.
Abstract:
The slow wave structure (SWS) of higher-order depressed magnetically insulated transmission line oscillator (HDMILO) is analyzed rigorously, and the electromagnetic field distribution is derived. High-frequency analysis results reveal that the degeneracy of two degenerate HEM11 modes is removed by the slot in SWS plate and the two degenerate modes split into two modes which polarize perpendicularly. Adjusting the azimuthal position of the slots destroys longitudinal oscillation condition of higher-order modes.
The slow wave structure (SWS) of higher-order depressed magnetically insulated transmission line oscillator (HDMILO) is analyzed rigorously, and the electromagnetic field distribution is derived. High-frequency analysis results reveal that the degeneracy of two degenerate HEM11 modes is removed by the slot in SWS plate and the two degenerate modes split into two modes which polarize perpendicularly. Adjusting the azimuthal position of the slots destroys longitudinal oscillation condition of higher-order modes.
2013,
25: 124-128.
Abstract:
In order to improve beam transmission efficiency for a four-rod radio frequency quadrupole (RFQ) accelerator, inter-electrode voltage distribution must be tuned and its accurate value need to be measured. Effect of tuning plates on inter-electrode voltage distribution was studied by electromagnetic numerical simulation, as the unflatness of the voltage distribution was caused by unevenly distributed capacitance and tuning plates could change the distributed inductance. The final inter-electrode voltage distribution was tuned to be better than 95%. In beam commissioning, inter-electrode voltage was determined by measuring the energy spectrum of X-ray and multiple energy peaks were studied by beam dynamics simulation. Input power was calibrated with beam commissioning results that 284 kW was needed in order to get 70 kV inter-electrode voltage.
In order to improve beam transmission efficiency for a four-rod radio frequency quadrupole (RFQ) accelerator, inter-electrode voltage distribution must be tuned and its accurate value need to be measured. Effect of tuning plates on inter-electrode voltage distribution was studied by electromagnetic numerical simulation, as the unflatness of the voltage distribution was caused by unevenly distributed capacitance and tuning plates could change the distributed inductance. The final inter-electrode voltage distribution was tuned to be better than 95%. In beam commissioning, inter-electrode voltage was determined by measuring the energy spectrum of X-ray and multiple energy peaks were studied by beam dynamics simulation. Input power was calibrated with beam commissioning results that 284 kW was needed in order to get 70 kV inter-electrode voltage.
2013,
25: 129-132.
Abstract:
Cold cathode RF electron guns based on field emissions combine the characteristics of thermo- and photo-cathode RF guns and may provide low emittance, high current electron beams. Studies of such a gun in the Institute of Applied Electronics, CAEP are presented here. The effective work function of diamond films is greatly reduced by doping so that valuable electron currents can be obtained at the presence of moderate electrical field strengths. A test RF gun was designed by taking into account many factors such as back-bombardment and accelerating efficiency. Particle tracking of such a gun was implemented and turned out that low emittance electron bunches can be obtained at the gun exit. However, the energy spectrum is not so good and needs improvement in the future.
Cold cathode RF electron guns based on field emissions combine the characteristics of thermo- and photo-cathode RF guns and may provide low emittance, high current electron beams. Studies of such a gun in the Institute of Applied Electronics, CAEP are presented here. The effective work function of diamond films is greatly reduced by doping so that valuable electron currents can be obtained at the presence of moderate electrical field strengths. A test RF gun was designed by taking into account many factors such as back-bombardment and accelerating efficiency. Particle tracking of such a gun was implemented and turned out that low emittance electron bunches can be obtained at the gun exit. However, the energy spectrum is not so good and needs improvement in the future.
2013,
25: 133-136.
Abstract:
In order to study the free-electron laser technology, an independently tunable cells thermionic-cathode RF gun with two microwave feed-in ports is manufactured in CAEP. An experiment facility of power test is built, and experiment research on beam current and power of back electron bombardment is performed. Research result shows that a beam intensity over 500 mA can be measured at exit of the RF gun, and the back electron bombardment can be changed with adjustment of phase and amplitude of the electric field in the first cavity.
In order to study the free-electron laser technology, an independently tunable cells thermionic-cathode RF gun with two microwave feed-in ports is manufactured in CAEP. An experiment facility of power test is built, and experiment research on beam current and power of back electron bombardment is performed. Research result shows that a beam intensity over 500 mA can be measured at exit of the RF gun, and the back electron bombardment can be changed with adjustment of phase and amplitude of the electric field in the first cavity.
2013,
25: 137-140.
Abstract:
This paper describes the Experimental Physics and Industrial Control System (EPICS) with the Channel Archiver. We build the data acquisition system for THz-FEL facility to access the experimental data efficiently through the study of Channel Archiver data archiving and retrieval models, and manage the historical data retrieval with the data recovery tool Archive Viewer. Thus a convenient storage and retrieval method is established for large amounts of data generated by the facility.
This paper describes the Experimental Physics and Industrial Control System (EPICS) with the Channel Archiver. We build the data acquisition system for THz-FEL facility to access the experimental data efficiently through the study of Channel Archiver data archiving and retrieval models, and manage the historical data retrieval with the data recovery tool Archive Viewer. Thus a convenient storage and retrieval method is established for large amounts of data generated by the facility.
2013,
25: 141-144.
Abstract:
The laser wire (LW) method has been demonstrated as an effective non-interceptive technique for measuring transverse electron beam size of CW FELs and ERLs. To measure the beam size of a CW DC gun, which is built as an electron source of FEL-THz facility in China Academy of Engineering Physics (CAEP), a high repetition LW system is proposed. The first prototype system is going to be installed at the exit of the DC gun, where the energy of electron beam is extremely low. In this paper, the LW system adapted to the FEL beam parameters is discussed, and the main parameters are given. With numerical calculation and Particle-in-Cell simulation, the high repetition LW system is proved to be lower-cost, higher-precision, faster-scanning and lower-influence than normal LW. The experiment proposal of the first high repetition LW is also introduced.
The laser wire (LW) method has been demonstrated as an effective non-interceptive technique for measuring transverse electron beam size of CW FELs and ERLs. To measure the beam size of a CW DC gun, which is built as an electron source of FEL-THz facility in China Academy of Engineering Physics (CAEP), a high repetition LW system is proposed. The first prototype system is going to be installed at the exit of the DC gun, where the energy of electron beam is extremely low. In this paper, the LW system adapted to the FEL beam parameters is discussed, and the main parameters are given. With numerical calculation and Particle-in-Cell simulation, the high repetition LW system is proved to be lower-cost, higher-precision, faster-scanning and lower-influence than normal LW. The experiment proposal of the first high repetition LW is also introduced.
2013,
25: 145-148.
Abstract:
A key technology issue of high-average-power free-electron laser (FEL) is the demonstration of stable, reliable, high-brightness, high-power electron source operation. The photocathode DC high voltage electron gun requires extreme-height-vacuum and more than 250 kV operating voltage. The vacuum vessel is a high conductance design, and the pump ability of NEGs can act well. To realize high voltage operating stability, the electrode system introduces a middle-potential electrode and the electric field strength can be depressed to 70 percent on the cathode support tube surface. Based on the design thoughts, the vacuum has been up to less than 510-9 Pa and the operating voltage reaches 300 kV without abnormity. In this report, we concentrate on the description of considerations for engineering design and some details of the photo-DC-Gun that have been proven fitting in practice.
A key technology issue of high-average-power free-electron laser (FEL) is the demonstration of stable, reliable, high-brightness, high-power electron source operation. The photocathode DC high voltage electron gun requires extreme-height-vacuum and more than 250 kV operating voltage. The vacuum vessel is a high conductance design, and the pump ability of NEGs can act well. To realize high voltage operating stability, the electrode system introduces a middle-potential electrode and the electric field strength can be depressed to 70 percent on the cathode support tube surface. Based on the design thoughts, the vacuum has been up to less than 510-9 Pa and the operating voltage reaches 300 kV without abnormity. In this report, we concentrate on the description of considerations for engineering design and some details of the photo-DC-Gun that have been proven fitting in practice.
2013,
25: 149-152.
Abstract:
According to requirements of physical parameters of undulator, we mainly design the size tolerance and structure of magnets and poles, the performance parameters of magnet and the measurement system of permanent magnet. The size tolerances of magnets and poles are 0.05 mm and 0.02 mm respectively along the beamline. The assembly and adjustment of magnets and poles are independent. At the same time, Helmhotz coils and magnetic field integral method are used to measure the magnet performance. Finally, the mechanical system and the gap adjustment system of the undulator are designed. It is found that the transom and bracket deformations are 1.5 m and 7.5 m respectively in the mechanical system. In the control system, clearance adjustment ranges from 18 mm to 32 mm, and adjustment precision and taper are 0.01 mm and 0.015 mm respectively.
According to requirements of physical parameters of undulator, we mainly design the size tolerance and structure of magnets and poles, the performance parameters of magnet and the measurement system of permanent magnet. The size tolerances of magnets and poles are 0.05 mm and 0.02 mm respectively along the beamline. The assembly and adjustment of magnets and poles are independent. At the same time, Helmhotz coils and magnetic field integral method are used to measure the magnet performance. Finally, the mechanical system and the gap adjustment system of the undulator are designed. It is found that the transom and bracket deformations are 1.5 m and 7.5 m respectively in the mechanical system. In the control system, clearance adjustment ranges from 18 mm to 32 mm, and adjustment precision and taper are 0.01 mm and 0.015 mm respectively.
2013,
25: 153-157.
Abstract:
The physics design of the undulator in high average power free electronic laser terahertz source is discussed. Hybrid Halbach structure is selected, after the period length, period quantity and peak magnetic field strength, etc. are fixed. The dimension of permanent magnet block is 8 cm1.3 cm6 cm, and the dimension of pole is 5 cm0.6 cm4.8 cm. The gap of the undulator is variable. While the gap range is 1.81-3.05 cm, the range of peak magnetic field strength is 0.529-0.184 T, and the length of good field area is 3.02-2.13 cm. Meanwhile, as the error of undulator magnetic field has effect on free electronic laser, the tolerances of undulator parameters are brought in, and the end design of the undulator is discussed at last.
The physics design of the undulator in high average power free electronic laser terahertz source is discussed. Hybrid Halbach structure is selected, after the period length, period quantity and peak magnetic field strength, etc. are fixed. The dimension of permanent magnet block is 8 cm1.3 cm6 cm, and the dimension of pole is 5 cm0.6 cm4.8 cm. The gap of the undulator is variable. While the gap range is 1.81-3.05 cm, the range of peak magnetic field strength is 0.529-0.184 T, and the length of good field area is 3.02-2.13 cm. Meanwhile, as the error of undulator magnetic field has effect on free electronic laser, the tolerances of undulator parameters are brought in, and the end design of the undulator is discussed at last.
2013,
25: 158-160.
Abstract:
The surface of the active layer of GaAs photocathode must reach the atomically clean surface before Cs-O activeness. The most effective method, which is used quite often, is the high-temperature thermal cleaning. It is very difficult to measure the surface temperature of a photocathode precisely in a vacuum system during the thermal cleaning. In this paper, we use ANSYS program to analyse GaAs photocathode during the thermal cleaning, with the temperature distribution on the photocathode surface obtained. We also discuss quantum efficiency distribution with the temperature distribution on the photocathode surface.
The surface of the active layer of GaAs photocathode must reach the atomically clean surface before Cs-O activeness. The most effective method, which is used quite often, is the high-temperature thermal cleaning. It is very difficult to measure the surface temperature of a photocathode precisely in a vacuum system during the thermal cleaning. In this paper, we use ANSYS program to analyse GaAs photocathode during the thermal cleaning, with the temperature distribution on the photocathode surface obtained. We also discuss quantum efficiency distribution with the temperature distribution on the photocathode surface.
2013,
25: 161-163.
Abstract:
The gallium arsenide wafer was activated by excessive-oxygen YOYO activation after high-temperature cleaning on the wafer. The quantum efficiency and the lifetime under laser illuminating were measured, and the maximum quantum efficiency was 4.66%. An average current over 1 mA was obtained in the DC-gun experiment. In the end, we discussed the reasons for vacuum degree, high temperature cleaning and Cs-O activating process causing the low maximum quantum efficiency and low lifetime of the gallium arsenide wafer.
The gallium arsenide wafer was activated by excessive-oxygen YOYO activation after high-temperature cleaning on the wafer. The quantum efficiency and the lifetime under laser illuminating were measured, and the maximum quantum efficiency was 4.66%. An average current over 1 mA was obtained in the DC-gun experiment. In the end, we discussed the reasons for vacuum degree, high temperature cleaning and Cs-O activating process causing the low maximum quantum efficiency and low lifetime of the gallium arsenide wafer.
2013,
25: 164-168.
Abstract:
The Marx generator especially makes use of inductive charging technology to ensure high-repetitive operation. Low-inductance capacitors of 3.3 nF are chosen as energy storage capacitors. And helix inductors are utilized as charging and grounding elements. By means of rapid discharge of each short gas spark gap, wave erection can be realized on the output load. The Marx is fitted into a tube with a diameter of 145 mm and a total length of 477 mm. The generator is pressurized with an N2/SF6 mixture. This system stores 7.9 J and is capable of delivering a current about 3.0 kA at 150 kV to a 50 load. The full width half maximum of output voltage is about 30 ns, and the rise time of the current is less than 10 ns. The repetitive frequency is 60 Hz.
The Marx generator especially makes use of inductive charging technology to ensure high-repetitive operation. Low-inductance capacitors of 3.3 nF are chosen as energy storage capacitors. And helix inductors are utilized as charging and grounding elements. By means of rapid discharge of each short gas spark gap, wave erection can be realized on the output load. The Marx is fitted into a tube with a diameter of 145 mm and a total length of 477 mm. The generator is pressurized with an N2/SF6 mixture. This system stores 7.9 J and is capable of delivering a current about 3.0 kA at 150 kV to a 50 load. The full width half maximum of output voltage is about 30 ns, and the rise time of the current is less than 10 ns. The repetitive frequency is 60 Hz.
2013,
25: 169-172.
Abstract:
Presently, the high power microwave(HPM) radiation systems are widely concerned by researchers, asa driver of HPM radiation system. Marx generator has the advantage because of its high output peak power, compact structure and small volume. This paper introduces the characteristics of a compact Marx generator with repetitive working frequency. Based on the theoretic analysis and experimental research, a 14-staged compact and repetitive Marx generator with inductive isolators is developed. It is charged synchronously with positive and negative constant current, and designed with spark switch and Marx high voltage insulation integrative, as well as omitted capacitance charging ground loop which makes the whole system concision and compact. According to debugging, its output voltage is up to 475 kV with a rise-time about 30 ns, and works stably in the repetitive frequency of 20 Hz when it fills with 0.16 MPa pure SF6.
Presently, the high power microwave(HPM) radiation systems are widely concerned by researchers, asa driver of HPM radiation system. Marx generator has the advantage because of its high output peak power, compact structure and small volume. This paper introduces the characteristics of a compact Marx generator with repetitive working frequency. Based on the theoretic analysis and experimental research, a 14-staged compact and repetitive Marx generator with inductive isolators is developed. It is charged synchronously with positive and negative constant current, and designed with spark switch and Marx high voltage insulation integrative, as well as omitted capacitance charging ground loop which makes the whole system concision and compact. According to debugging, its output voltage is up to 475 kV with a rise-time about 30 ns, and works stably in the repetitive frequency of 20 Hz when it fills with 0.16 MPa pure SF6.
2013,
25: 173-176.
Abstract:
In order to enhance the working voltage of pseudospark switch, a two-staged pseudospark switch triggered by glow discharge is designed. The design of the switch is comprised of the anode, cathode, grid electrode and glow discharge cavity. The two-staged pseudospark switch is formed by adopting middle grid electrode. The middle grid electrode uses a flat plate, with a thickness of 1.5 mm. The grid holes with a size of 1 mm each are distributed on a ring with a diameter of 5 mm. The glow discharge cavity is devised to work on the left region of Paschen curve, with the characteristics of large discharge current and low trigger voltage. Experiment shows that the RC voltage even assignment is needed for the switch and it can make the anode voltage divide equally in the two gaps. Then the switch can be triggered reliably with the anode voltage from 1 kV to 57 kV. When the anode is charged to 57 kV, the output voltage on the 50 resistor load is 56 kV, and the jitter is about 1.4ns.
In order to enhance the working voltage of pseudospark switch, a two-staged pseudospark switch triggered by glow discharge is designed. The design of the switch is comprised of the anode, cathode, grid electrode and glow discharge cavity. The two-staged pseudospark switch is formed by adopting middle grid electrode. The middle grid electrode uses a flat plate, with a thickness of 1.5 mm. The grid holes with a size of 1 mm each are distributed on a ring with a diameter of 5 mm. The glow discharge cavity is devised to work on the left region of Paschen curve, with the characteristics of large discharge current and low trigger voltage. Experiment shows that the RC voltage even assignment is needed for the switch and it can make the anode voltage divide equally in the two gaps. Then the switch can be triggered reliably with the anode voltage from 1 kV to 57 kV. When the anode is charged to 57 kV, the output voltage on the 50 resistor load is 56 kV, and the jitter is about 1.4ns.
2013,
25: 177-180.
Abstract:
A 10-staged low impedance Marx generator is designed, the volume of the generator is about 0.5 m3 and the output power and pulse width are more than 30 GW and 200 ns. The compact pulsed power system contains 10 bipolar (50 kV) stages of capacitors and rail switches placed in a tank filled with dielectric oil. The positive and negative electrodes of the capacitor are suppressed within the switchs electrode. This system stores 5 kJ and is capable of delivering a current up to 41.6 kA at 500 kV to a 12 load. The rise time of the current is less than 100 ns. The system size is 1.2 m0.5 m0.6 m. In this paper, the experimental results with resistive load are presented as well as data obtained when the obtained Marx generator is coupled to high power microwave tubes. A microwave output power of about 400 MW is got at 1.23 GHz. The radiation mode is TM01, and pulse width is 60 ns.
A 10-staged low impedance Marx generator is designed, the volume of the generator is about 0.5 m3 and the output power and pulse width are more than 30 GW and 200 ns. The compact pulsed power system contains 10 bipolar (50 kV) stages of capacitors and rail switches placed in a tank filled with dielectric oil. The positive and negative electrodes of the capacitor are suppressed within the switchs electrode. This system stores 5 kJ and is capable of delivering a current up to 41.6 kA at 500 kV to a 12 load. The rise time of the current is less than 100 ns. The system size is 1.2 m0.5 m0.6 m. In this paper, the experimental results with resistive load are presented as well as data obtained when the obtained Marx generator is coupled to high power microwave tubes. A microwave output power of about 400 MW is got at 1.23 GHz. The radiation mode is TM01, and pulse width is 60 ns.
