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RSS2015 Vol. 27, No. 06
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2015,
27: 061001.
doi: 10.11884/HPLPB201527.061001
Abstract:
The INNOSLAB in-band pumping picosecond amplification laser system is studied with flake Nd: YVO4 crystal. A new method for mode-matching was demonstrated to simplify the amplifier design, integrating the benefits of the in-band pumping technique and the excellent thermal management of the INNOSLAB amplifier design. As a result, an average of 60.7 W, pulse width of 16.8 ps, repetition frequency of 20 MHz laser was achieved with optic to optic efficiency of 25.3%. The beam quality of 1.55 was obtained with 50 W output laser.
The INNOSLAB in-band pumping picosecond amplification laser system is studied with flake Nd: YVO4 crystal. A new method for mode-matching was demonstrated to simplify the amplifier design, integrating the benefits of the in-band pumping technique and the excellent thermal management of the INNOSLAB amplifier design. As a result, an average of 60.7 W, pulse width of 16.8 ps, repetition frequency of 20 MHz laser was achieved with optic to optic efficiency of 25.3%. The beam quality of 1.55 was obtained with 50 W output laser.
2015,
27: 061002.
doi: 10.11884/HPLPB201527.061002
Abstract:
The physical process of filled-aperture coherent beam combining (CBC) using diffractive optical elements (DOEs) is analyzed. The mathematical model of CBC based on DOEs is build up, and the relationship between the complex amplitude of the combined beam and the phase distribution of the DOEs is deduced. The uniformity of the intensity of combined beam is used as the evaluation function of the iteration, and the phase distributions of the one-dimensional diffractive beam combiners are calculated. Compared with the reported DOEs beam splitters, these beam combiners can achieve higher combining efficiency. The phase distributions of the beam combiners are optimized using both simulated annealing algorithm and stochastic parallel gradient descent algorithm, and the computational efficiency is significantly improved. The phase distribution and combining efficiency of multi-beam diffractive beam combiners are presented. The impacts of single disabled beam and surface error of the DOEs on the combining efficiency are analyzed. The simulation results expose that with the increasing number of component beams the impact of single disabled beam on combining efficiency decreases, and the RMS wavefront error of the DOEs should be less than 1/28 of the wavelength in order to make combining efficiency degradation less than 5%.
The physical process of filled-aperture coherent beam combining (CBC) using diffractive optical elements (DOEs) is analyzed. The mathematical model of CBC based on DOEs is build up, and the relationship between the complex amplitude of the combined beam and the phase distribution of the DOEs is deduced. The uniformity of the intensity of combined beam is used as the evaluation function of the iteration, and the phase distributions of the one-dimensional diffractive beam combiners are calculated. Compared with the reported DOEs beam splitters, these beam combiners can achieve higher combining efficiency. The phase distributions of the beam combiners are optimized using both simulated annealing algorithm and stochastic parallel gradient descent algorithm, and the computational efficiency is significantly improved. The phase distribution and combining efficiency of multi-beam diffractive beam combiners are presented. The impacts of single disabled beam and surface error of the DOEs on the combining efficiency are analyzed. The simulation results expose that with the increasing number of component beams the impact of single disabled beam on combining efficiency decreases, and the RMS wavefront error of the DOEs should be less than 1/28 of the wavelength in order to make combining efficiency degradation less than 5%.
2015,
27: 061003.
doi: 10.11884/HPLPB201527.061003
Abstract:
Because the distribution of temperature field was not uniform during the processing of welding, the stress, microstructure and performances in different regions in the welded joints were different. And there ware residual tensile stress which might cause to stress corrosion cracking (SCC). The 316 austenitic stainless steel welded joints were treated by laser shock peening. In order to protect the welded joints from stress corrosion cracking, the laser shock waves were designed with different strengths in the weld, heat affected zone (HAZ) and the matrix. Under a constant temperature of 90 ℃, the performance of stress corrosion cracking of 316 stainless steel was studied in FeCl3 solution. The welded specimens cracked within 112 h. After laser shock peening the crack time was increased by 33.48%. The mechanisms were analyzed from residual stress tests and microstructure observation. It was found that the residual tensile stress was eliminated in HAZ. There were residual compressive stress and the stress gradient was reduced from 54.7MPa/mm to 11.7MPa/mm which were beneficial for protecting weldments against SCC. On the other hand, the microstructure and mechanical property of the welded joints after laser shock peening became uniform. The grain refining would delay crack initiation and propagation. All in all, the residual compressive stress and uniform microstructure caused by laser shock peening would protect the welded joints against stress corrosion cracking.
Because the distribution of temperature field was not uniform during the processing of welding, the stress, microstructure and performances in different regions in the welded joints were different. And there ware residual tensile stress which might cause to stress corrosion cracking (SCC). The 316 austenitic stainless steel welded joints were treated by laser shock peening. In order to protect the welded joints from stress corrosion cracking, the laser shock waves were designed with different strengths in the weld, heat affected zone (HAZ) and the matrix. Under a constant temperature of 90 ℃, the performance of stress corrosion cracking of 316 stainless steel was studied in FeCl3 solution. The welded specimens cracked within 112 h. After laser shock peening the crack time was increased by 33.48%. The mechanisms were analyzed from residual stress tests and microstructure observation. It was found that the residual tensile stress was eliminated in HAZ. There were residual compressive stress and the stress gradient was reduced from 54.7MPa/mm to 11.7MPa/mm which were beneficial for protecting weldments against SCC. On the other hand, the microstructure and mechanical property of the welded joints after laser shock peening became uniform. The grain refining would delay crack initiation and propagation. All in all, the residual compressive stress and uniform microstructure caused by laser shock peening would protect the welded joints against stress corrosion cracking.
2015,
27: 061004.
doi: 10.11884/HPLPB201527.061004
Abstract:
This paper carries out researches on the chemical etching of HF acid on K9 substrates and calibrates the etching rate of HF acid under the concentration of 40% and 2%. The relationship between surface morphology of substrate and etching depth is analyzed and the effect of etching time, concentration of HF acid, ultrasonic cleaning on the LIDT is investigated. The optimized etching cleaning process which can reduce the deposition of silicate effectively and improve the LIDT is proposed. Finally, the optimized etching cleaning process is used to test and verify the experimental results. The results indicate that under the irradiation of 1064 nm laser, the LIDT of K9 substrates etched for 90s under the condition of high temperature and ultrasonic with 2% concentration HF acid is 75% higher than the original one.
This paper carries out researches on the chemical etching of HF acid on K9 substrates and calibrates the etching rate of HF acid under the concentration of 40% and 2%. The relationship between surface morphology of substrate and etching depth is analyzed and the effect of etching time, concentration of HF acid, ultrasonic cleaning on the LIDT is investigated. The optimized etching cleaning process which can reduce the deposition of silicate effectively and improve the LIDT is proposed. Finally, the optimized etching cleaning process is used to test and verify the experimental results. The results indicate that under the irradiation of 1064 nm laser, the LIDT of K9 substrates etched for 90s under the condition of high temperature and ultrasonic with 2% concentration HF acid is 75% higher than the original one.
2015,
27: 061005.
doi: 10.11884/HPLPB201527.061005
Abstract:
In this paper, we study the thermal effects of side-pump large energy solid state laser. We set up a numerical model of LDA side pump Nd:YAG laser rod. Using Ansys program, the finite element method is adopted to analyze the time-varying thermal effect for pulse pump solid-state laser. The steady temperature field and the transient temperature field distribution are simulated, and the changing rule of the distribution of temperature field in the medium is summarized. We calculate the thermal focal length caused by thermal gradient, stress birefringence, and the end effect of medium respectively. The research results show that the thermal effect of LDA side pump laser show time-varying characteristics, the center temperature in cross section of medium have a zigzag periodical change, and the frequency equals to LDA pump frequency. The steady-state distribution is influenced by LDA pump parameters greatly. The thermal lens effect is mainly caused by the temperature gradient in the medium. This study could provide a theoretical guidance for the design of thermal-stable laser resonator and compensation of thermal effect.
In this paper, we study the thermal effects of side-pump large energy solid state laser. We set up a numerical model of LDA side pump Nd:YAG laser rod. Using Ansys program, the finite element method is adopted to analyze the time-varying thermal effect for pulse pump solid-state laser. The steady temperature field and the transient temperature field distribution are simulated, and the changing rule of the distribution of temperature field in the medium is summarized. We calculate the thermal focal length caused by thermal gradient, stress birefringence, and the end effect of medium respectively. The research results show that the thermal effect of LDA side pump laser show time-varying characteristics, the center temperature in cross section of medium have a zigzag periodical change, and the frequency equals to LDA pump frequency. The steady-state distribution is influenced by LDA pump parameters greatly. The thermal lens effect is mainly caused by the temperature gradient in the medium. This study could provide a theoretical guidance for the design of thermal-stable laser resonator and compensation of thermal effect.
2015,
27: 061006.
doi: 10.11884/HPLPB201527.061006
Abstract:
The evolution hardware as a new hardware carrier, having self-organizing, adaptive, self-repair ability, is an important application of artificial intelligence in the controller of high energy laser. Genetic algorithm is one of the important factors that influence the hardware evolution speed. For the problems of long evolutionary time and large amount of computation of traditional genetic algorithm, an improved genetic algorithmPopulation Hybridization Monkey-King Genetic Algorithm (PHMKGA)was proposed. Inspired by hybrid vigor in biological species, gene sequences in the PHMKGA were divided into Nd independent evolution sub populations while evolving. Each sub population was formed by evolving according to Monkey-King Genetic Algorithm from the original population; the Monkey king genes of sub populations were exchanged to be repeated Monkey King genetic operation; the offsprings of heterosis were produced in sub population. Analysis shows that the PHMKGA(Nd is the number of sub population)could reduce the computation of gene ordering in each generation to 1/Nd comparing to Monkey-King Genetic Algorithm, and is more conducive to the realization of parallel. The simulation analysis based on MATLAB and Modelsim indicates that the PHMKGA results in faster convergence speed and better evolution.
The evolution hardware as a new hardware carrier, having self-organizing, adaptive, self-repair ability, is an important application of artificial intelligence in the controller of high energy laser. Genetic algorithm is one of the important factors that influence the hardware evolution speed. For the problems of long evolutionary time and large amount of computation of traditional genetic algorithm, an improved genetic algorithmPopulation Hybridization Monkey-King Genetic Algorithm (PHMKGA)was proposed. Inspired by hybrid vigor in biological species, gene sequences in the PHMKGA were divided into Nd independent evolution sub populations while evolving. Each sub population was formed by evolving according to Monkey-King Genetic Algorithm from the original population; the Monkey king genes of sub populations were exchanged to be repeated Monkey King genetic operation; the offsprings of heterosis were produced in sub population. Analysis shows that the PHMKGA(Nd is the number of sub population)could reduce the computation of gene ordering in each generation to 1/Nd comparing to Monkey-King Genetic Algorithm, and is more conducive to the realization of parallel. The simulation analysis based on MATLAB and Modelsim indicates that the PHMKGA results in faster convergence speed and better evolution.
2015,
27: 061007.
doi: 10.11884/HPLPB201527.061007
Abstract:
Based on the principles of supervised evaluation method, the paper puts forward three evaluation indices of the high resolution remote sensing image segmentation: precision, recall and relative similarity, and brings forward the method of precision evaluation of remote sensing image segmentation. With respect to the reference object matching problem of the supervised evaluation method, the paper proposes the matching method of bidirectional local optimal object. Validation of the proposed evaluation indices is carried out using GF-1 high resolution remote sensing image in Huainan city, Anhui province, China. The results show that the proposed evaluation indices can reflect very well the quality of the segmentation results and are consistent with the real distribution of ground landcover segmentation, and also provide the basic reference to parameter setting for the image segmentation algorithm and optimal scale selection for the multi-scale segmentation.
Based on the principles of supervised evaluation method, the paper puts forward three evaluation indices of the high resolution remote sensing image segmentation: precision, recall and relative similarity, and brings forward the method of precision evaluation of remote sensing image segmentation. With respect to the reference object matching problem of the supervised evaluation method, the paper proposes the matching method of bidirectional local optimal object. Validation of the proposed evaluation indices is carried out using GF-1 high resolution remote sensing image in Huainan city, Anhui province, China. The results show that the proposed evaluation indices can reflect very well the quality of the segmentation results and are consistent with the real distribution of ground landcover segmentation, and also provide the basic reference to parameter setting for the image segmentation algorithm and optimal scale selection for the multi-scale segmentation.
2015,
27: 061008.
doi: 10.11884/HPLPB201527.061008
Abstract:
The XeF(CA) laser has many potential applications in laser underwater detecting due to the fact that its wavelength located in 450~520 nm band is the best propagating window in atmosphere and sea. The technique of surface discharge optical pumping possesses many advantages, such as intense violet and vacuum-violet radiation, relatively low charge voltage, non-essential high current switch, high temperature and high repetition rate, and easy realization in technique. Therefore it becomes a highly efficient pumping for Xe(CA) laser. Intense shockwave is generated during the expansion of plasma induced by surface discharge. The intense shockwave results in the turbulence of homogeneity and refractive index of active medium, and impacts on the output of XeF laser consequently. Therefore, it is important to study the properties of generation and propagation of the shockwave. By employing a pressure sensor, properties of the shockwave measured at various spots and discharge voltages are analyzed. The results indicate that the duration of the shockwave, followed by a relatively weaker pressure wave, is in the ms range. The higher the charge voltage and the more the released energy, the higher the peak pressure of the shockwave with the maximum pressure of up to 1 MPa, the more the peak position delayed, and the longer the duration. The research points out a direction for improving the output stability of XeF(CA) laser at relatively high repetition rate.
The XeF(CA) laser has many potential applications in laser underwater detecting due to the fact that its wavelength located in 450~520 nm band is the best propagating window in atmosphere and sea. The technique of surface discharge optical pumping possesses many advantages, such as intense violet and vacuum-violet radiation, relatively low charge voltage, non-essential high current switch, high temperature and high repetition rate, and easy realization in technique. Therefore it becomes a highly efficient pumping for Xe(CA) laser. Intense shockwave is generated during the expansion of plasma induced by surface discharge. The intense shockwave results in the turbulence of homogeneity and refractive index of active medium, and impacts on the output of XeF laser consequently. Therefore, it is important to study the properties of generation and propagation of the shockwave. By employing a pressure sensor, properties of the shockwave measured at various spots and discharge voltages are analyzed. The results indicate that the duration of the shockwave, followed by a relatively weaker pressure wave, is in the ms range. The higher the charge voltage and the more the released energy, the higher the peak pressure of the shockwave with the maximum pressure of up to 1 MPa, the more the peak position delayed, and the longer the duration. The research points out a direction for improving the output stability of XeF(CA) laser at relatively high repetition rate.
2015,
27: 061009.
doi: 10.11884/HPLPB201527.061009
Abstract:
Forecasting upper air optical turbulence has important significance in optical engineering applications. This paper introduces the running processes of Weather Research and Forecasting Mode (WRF), mode installation, and simulation parameter settings. Combine with optical turbulence parameterization schemes, the atmospheric optical turbulence intensity profile was forecasted and compared with the measured data by balloons. The result shows that: the forecasted atmospheric optical turbulence intensity profiles are in line with the general characteristics and regularity of the upper air optical turbulence, but their shapes have some differences. the analysis on the causes of the differences is made, which shows it is necessary to further modify the forecasting model and the calculation of atmospheric optical turbulence.
Forecasting upper air optical turbulence has important significance in optical engineering applications. This paper introduces the running processes of Weather Research and Forecasting Mode (WRF), mode installation, and simulation parameter settings. Combine with optical turbulence parameterization schemes, the atmospheric optical turbulence intensity profile was forecasted and compared with the measured data by balloons. The result shows that: the forecasted atmospheric optical turbulence intensity profiles are in line with the general characteristics and regularity of the upper air optical turbulence, but their shapes have some differences. the analysis on the causes of the differences is made, which shows it is necessary to further modify the forecasting model and the calculation of atmospheric optical turbulence.
2015,
27: 061010.
doi: 10.11884/HPLPB201527.061010
Abstract:
Based on the transverse flow characteristic of supersonic chemical oxygen iodine laser gain medium, the optical resonator with gain negative feedback structure has been designed. Through coupling simulation of the chemical reaction supersonic flow field and light field, and depending on the laser operation parameters, the feasibility of this structure to realize the pulse laser has been demonstrated. The results show that when the oscillation laser in the gain area upstream is amplified the more times and energy extraction ability for the upstream gain medium is stronger, the pulse modulation effect is more significant. Using structural design that the laser spot is narrowed and then expanded, the peak power of the pulse laser will increase 10 to 20 times, which theoretically proves the modulation method of the gain negative feedback can realize the transverse flow laser with the pulse laser output.
Based on the transverse flow characteristic of supersonic chemical oxygen iodine laser gain medium, the optical resonator with gain negative feedback structure has been designed. Through coupling simulation of the chemical reaction supersonic flow field and light field, and depending on the laser operation parameters, the feasibility of this structure to realize the pulse laser has been demonstrated. The results show that when the oscillation laser in the gain area upstream is amplified the more times and energy extraction ability for the upstream gain medium is stronger, the pulse modulation effect is more significant. Using structural design that the laser spot is narrowed and then expanded, the peak power of the pulse laser will increase 10 to 20 times, which theoretically proves the modulation method of the gain negative feedback can realize the transverse flow laser with the pulse laser output.
2015,
27: 061011.
doi: 10.11884/HPLPB201527.061011
Abstract:
Target detection in smoke environment using laser active imaging is of great significance. Suppressing scattering effect of light effectively is the key to improve the imaging quality. According to the polarization theory of light, the polarization characteristics of a single-scattering photon changing with the scattering angle is analyzed, and the polarization characteristics of light transmitting in the smoke environment is simulated. The polarization difference method is proposed to suppress scattering light and an imaging experiment is set up at last. It is shown that when light is transmitting in smoke, the scattering light is mainly made up of small-angle scattering light, which still retains the initial polarization characteristics of the incident light. Compared with the direct imaging method, the polarization difference method can effectively filter out the influence of small-angle scattering light and enhance the detailed information of imaging target and the image contrast.
Target detection in smoke environment using laser active imaging is of great significance. Suppressing scattering effect of light effectively is the key to improve the imaging quality. According to the polarization theory of light, the polarization characteristics of a single-scattering photon changing with the scattering angle is analyzed, and the polarization characteristics of light transmitting in the smoke environment is simulated. The polarization difference method is proposed to suppress scattering light and an imaging experiment is set up at last. It is shown that when light is transmitting in smoke, the scattering light is mainly made up of small-angle scattering light, which still retains the initial polarization characteristics of the incident light. Compared with the direct imaging method, the polarization difference method can effectively filter out the influence of small-angle scattering light and enhance the detailed information of imaging target and the image contrast.
2015,
27: 061012.
doi: 10.11884/HPLPB201527.061012
Abstract:
The high coupling-efficiency fiber coupled diode laser module is obtained by beam shaping. The wavelength of the CW diode laser bar is 976 nm, and five bars are collimated by a fast axis collimation lens. Then the beams are transformed and collimated by slow axis collimation optics. Then all the beams are combined in space, and focused into a multimode fiber (400 m core diameter, the numerical aperture (NA) is 0.22). Experimental results show that the laser output from fiber could reach 327 W, and the coupling-efficiency is more than 93.6%. Experimental results demonstrate that this module lays a foundation for multi-wavelength, polarization beam combining and the high beam quality, high coupling efficiency diode laser module with CW thousands watts class output power can be developed.
The high coupling-efficiency fiber coupled diode laser module is obtained by beam shaping. The wavelength of the CW diode laser bar is 976 nm, and five bars are collimated by a fast axis collimation lens. Then the beams are transformed and collimated by slow axis collimation optics. Then all the beams are combined in space, and focused into a multimode fiber (400 m core diameter, the numerical aperture (NA) is 0.22). Experimental results show that the laser output from fiber could reach 327 W, and the coupling-efficiency is more than 93.6%. Experimental results demonstrate that this module lays a foundation for multi-wavelength, polarization beam combining and the high beam quality, high coupling efficiency diode laser module with CW thousands watts class output power can be developed.
2015,
27: 061013.
doi: 10.11884/HPLPB201527.061013
Abstract:
Estimation of the wind velocity from weak aerosol backscattering signals is a key problem in the coherent wind lidar. The Cramer-Rao lower bound (CRLB) of the maximum likelihood (ML) discrete spectral peak (DSP) estimation is discussed based on the statistical model of the covariance matrix of zero mean complex Gaussian random process of the backscattering signal. The CRLBs of both the ML DSP and Fisher information matrix are compared. On the condition of the covariance matrix statistical model of the backscattering signals in coherent wind lidar, the performance of the ML DSP estimation is examined by employing the computer Monte Carlo simulations, and the probability density function of the estimations of the wind velocity is researched as well. The effects of signal-to-noise ratio, the accumulation number of the laser pulse as well as pulse width of the outgoing laser pulse on ML DSP wind velocity estimations are illustrated respectively. The calculation and simulation results show that, (1)The CRLB of the ML DSP estimation is lower than the exact CRLB from Fisher information matrix; (2)Both of the fractions of the bad estimations are 0, and the standard deviations of the good estimations are 0.62 m/s and 0.50 m/s, respectively, for SNR of －20 dB and 100 laser pulses accumulation and SNR of －30 dB and 10 000 laser pulses accumulation.
Estimation of the wind velocity from weak aerosol backscattering signals is a key problem in the coherent wind lidar. The Cramer-Rao lower bound (CRLB) of the maximum likelihood (ML) discrete spectral peak (DSP) estimation is discussed based on the statistical model of the covariance matrix of zero mean complex Gaussian random process of the backscattering signal. The CRLBs of both the ML DSP and Fisher information matrix are compared. On the condition of the covariance matrix statistical model of the backscattering signals in coherent wind lidar, the performance of the ML DSP estimation is examined by employing the computer Monte Carlo simulations, and the probability density function of the estimations of the wind velocity is researched as well. The effects of signal-to-noise ratio, the accumulation number of the laser pulse as well as pulse width of the outgoing laser pulse on ML DSP wind velocity estimations are illustrated respectively. The calculation and simulation results show that, (1)The CRLB of the ML DSP estimation is lower than the exact CRLB from Fisher information matrix; (2)Both of the fractions of the bad estimations are 0, and the standard deviations of the good estimations are 0.62 m/s and 0.50 m/s, respectively, for SNR of －20 dB and 100 laser pulses accumulation and SNR of －30 dB and 10 000 laser pulses accumulation.
2015,
27: 061014.
doi: 10.11884/HPLPB201527.061014
Abstract:
A novel acceleration sensor based on a chirped-fiber Bragg grating( CFBG) has been proposed. It is mainly constituted by a rectangular cantilever beam sensing mechanism, a fiber optic spectrometer and a photodetector(PD). The expression of relationship between the acceleration and the bandwidth is derived. The acceleration can be obtained by measuring the bandwidth and voltage of the PD. The experimental results show that the reflection spectrum bandwidth and voltage of the PD are insensitive to temperature changes within the measuring range, there is a good linear relationship between the bandwidth of the reflection spectrum and the measured acceleration within a large range up to 0~700 m/s2, but the reflected optical power succeeds only below 350 m/s2 due to the decay in reflectivity when the bandwidth of the FBG is broadened significantly. The achieved sensitivities are 0.005 6 nmm-1s-2and 0.785 6 mVm-1s-2 for bandwidth and optical power measurements, respectively.
A novel acceleration sensor based on a chirped-fiber Bragg grating( CFBG) has been proposed. It is mainly constituted by a rectangular cantilever beam sensing mechanism, a fiber optic spectrometer and a photodetector(PD). The expression of relationship between the acceleration and the bandwidth is derived. The acceleration can be obtained by measuring the bandwidth and voltage of the PD. The experimental results show that the reflection spectrum bandwidth and voltage of the PD are insensitive to temperature changes within the measuring range, there is a good linear relationship between the bandwidth of the reflection spectrum and the measured acceleration within a large range up to 0~700 m/s2, but the reflected optical power succeeds only below 350 m/s2 due to the decay in reflectivity when the bandwidth of the FBG is broadened significantly. The achieved sensitivities are 0.005 6 nmm-1s-2and 0.785 6 mVm-1s-2 for bandwidth and optical power measurements, respectively.
2015,
27: 061015.
doi: 10.11884/HPLPB201527.061015
Abstract:
Planar waveguide laser has been one of the most promising high power solid-state lasers, due to its outstanding performance in terms of large mode volume and one dimension being confined. The current status and future perspectives of planar waveguide lasers at home and abroad are reviewed. Some attractive structures of planar waveguides are compared and discussed in detail, including double-clad waveguide configuration, the tapered structure waveguide and the self-imaging structure. The advancements of high power planar waveguide lasers as well as some limitations are analyzed.
Planar waveguide laser has been one of the most promising high power solid-state lasers, due to its outstanding performance in terms of large mode volume and one dimension being confined. The current status and future perspectives of planar waveguide lasers at home and abroad are reviewed. Some attractive structures of planar waveguides are compared and discussed in detail, including double-clad waveguide configuration, the tapered structure waveguide and the self-imaging structure. The advancements of high power planar waveguide lasers as well as some limitations are analyzed.
2015,
27: 061016.
doi: 10.11884/HPLPB201527.061016
Abstract:
The thermal field of metal plates in air flows under laser irradiation was computed. The numerical simulation was based on fluid-solid coupling method. The two phase flow model was used to simulate the scouring effect. It employed an implicit finite-volume, Gauss-Seidel scheme for solving the Reynolds averaged Navier-Stokes equations and solid energy equation in a coupled manner. The k- turbulence model was used for turbulence simulation. The physical process of laser ablation was described commendably with this method. The results of the thermal field and morphologies at different flow speed are presented in this paper. The results of two phase flow model and dynamic mesh model are compared and discussed. The results indicate that although the two models have the same thermal field results, the two phase flow model is more fit for physical process of laser ablation characterization.
The thermal field of metal plates in air flows under laser irradiation was computed. The numerical simulation was based on fluid-solid coupling method. The two phase flow model was used to simulate the scouring effect. It employed an implicit finite-volume, Gauss-Seidel scheme for solving the Reynolds averaged Navier-Stokes equations and solid energy equation in a coupled manner. The k- turbulence model was used for turbulence simulation. The physical process of laser ablation was described commendably with this method. The results of the thermal field and morphologies at different flow speed are presented in this paper. The results of two phase flow model and dynamic mesh model are compared and discussed. The results indicate that although the two models have the same thermal field results, the two phase flow model is more fit for physical process of laser ablation characterization.
2015,
27: 061017.
doi: 10.11884/HPLPB201527.061017
Abstract:
The rate equations model of diode pumped metastable rare gas laser(DPRGL) is established, and taking an argon DPRGL as an example, the influence of pump intensity, metastable atom density and gain medium length on characteristics of DPRGL are simulated and discussed. The results indicate that the DPRGL has a laser efficiency higher than 55% in theory under high pump intensity (~kW/cm2). Influence of metastable atom density and length of gain medium on the DPRGL is equivalent. Main important laser parameters need to be optimized harmoniously to obtain optimal optical conversion efficiency of the DPRGL.
The rate equations model of diode pumped metastable rare gas laser(DPRGL) is established, and taking an argon DPRGL as an example, the influence of pump intensity, metastable atom density and gain medium length on characteristics of DPRGL are simulated and discussed. The results indicate that the DPRGL has a laser efficiency higher than 55% in theory under high pump intensity (~kW/cm2). Influence of metastable atom density and length of gain medium on the DPRGL is equivalent. Main important laser parameters need to be optimized harmoniously to obtain optimal optical conversion efficiency of the DPRGL.
2015,
27: 061018.
doi: 10.11884/HPLPB201527.061018
Abstract:
Based on polarization beam combination technology, system analysis and quantitative calculation of several main system errors in the process of beam combination are conducted to improve the combining efficiency. The results show that, compared to overlap error, tilt angle and absorption loss of the polarization beam combiner, the adjustment error of half-wave plate is the main factor causing the decline of combining efficiency. If the loss of polarization beam combiner is 0.015, the inclination of incident beams is 2, and the overlap error is 5%, the coherent polarization beam combining efficiency of sixteen beams can be controlled more than 92.5%. When the deviation of the optical axis of half-wave plates is 0.045 rad, even without other errors, the combining efficiency will drop below 74%.
Based on polarization beam combination technology, system analysis and quantitative calculation of several main system errors in the process of beam combination are conducted to improve the combining efficiency. The results show that, compared to overlap error, tilt angle and absorption loss of the polarization beam combiner, the adjustment error of half-wave plate is the main factor causing the decline of combining efficiency. If the loss of polarization beam combiner is 0.015, the inclination of incident beams is 2, and the overlap error is 5%, the coherent polarization beam combining efficiency of sixteen beams can be controlled more than 92.5%. When the deviation of the optical axis of half-wave plates is 0.045 rad, even without other errors, the combining efficiency will drop below 74%.
2015,
27: 061019.
doi: 10.11884/HPLPB201527.061019
Abstract:
Crosstalk is the key parameter affecting the imaging quality of CMOS array detector in imaging applications. In order to understand the impact of crosstalk on the response of devices, the characteristics of electrical crosstalk of the CMOS image sensors are analyzed. The mathematical analysis model of the electrical crosstalk is established, and the amplitude of electrical crosstalk is calculated. The effects of parameters (including diffusion length, active area, depletion depth, pixel size and temperature) on the electrical crosstalk are studied. The results show that active area, depletion depth and pixel size have a bigger impact on electrical crosstalk compared with diffusion length and temperature. When the active area changes from 3.8 m2 up to 12.8 m2, the electrical crosstalk reduces about 13%; the change of pixel size, from 7 m7 m to 15 m15 m, makes it increase by 95.4%; and the temperature rises from 100 K to 180 K, the electrical crosstalk decreases by 0.6%.
Crosstalk is the key parameter affecting the imaging quality of CMOS array detector in imaging applications. In order to understand the impact of crosstalk on the response of devices, the characteristics of electrical crosstalk of the CMOS image sensors are analyzed. The mathematical analysis model of the electrical crosstalk is established, and the amplitude of electrical crosstalk is calculated. The effects of parameters (including diffusion length, active area, depletion depth, pixel size and temperature) on the electrical crosstalk are studied. The results show that active area, depletion depth and pixel size have a bigger impact on electrical crosstalk compared with diffusion length and temperature. When the active area changes from 3.8 m2 up to 12.8 m2, the electrical crosstalk reduces about 13%; the change of pixel size, from 7 m7 m to 15 m15 m, makes it increase by 95.4%; and the temperature rises from 100 K to 180 K, the electrical crosstalk decreases by 0.6%.
2015,
27: 061020.
doi: 10.11884/HPLPB201527.061020
Abstract:
The transient stimulated Brillouin scattering (SBS) process was studied based on the coupled-wave theory. The time-varying distributions of the intensities of pump light, Stokes light and induced stress were obtained by solving the nonlinear coupled-wave equations with the finite difference method. The effect of wavelength, as well as the intensities of pump light and Stokes light, on SBS process are investigated, the results shows the Stokes light takes effect in initial stage mainly, while the pump light works in steady stage; And the stress induced by SBS process varies largely with different wavelength. In addition, the shorter wavelength is, the faster stress develops, which results in damage to materials easier; The induced stress by 3 laser is 100 times as large as the lasers. The moment that SBS occurs for 3 laser is 15ns earlier than that for 2 laser.
The transient stimulated Brillouin scattering (SBS) process was studied based on the coupled-wave theory. The time-varying distributions of the intensities of pump light, Stokes light and induced stress were obtained by solving the nonlinear coupled-wave equations with the finite difference method. The effect of wavelength, as well as the intensities of pump light and Stokes light, on SBS process are investigated, the results shows the Stokes light takes effect in initial stage mainly, while the pump light works in steady stage; And the stress induced by SBS process varies largely with different wavelength. In addition, the shorter wavelength is, the faster stress develops, which results in damage to materials easier; The induced stress by 3 laser is 100 times as large as the lasers. The moment that SBS occurs for 3 laser is 15ns earlier than that for 2 laser.
2015,
27: 061021.
doi: 10.11884/HPLPB201527.061021
Abstract:
In order to study the effect of the defects on damage threshold of the surface, we modeled a classical three-dimension defect which is similar to the circular cone protuberance and calculated the electric field around this kind of defects by finite-difference method. Based on the field effect theory we calculated the damage thresholds of surfaces with different size defects. It can be got that the electric fields were amplified obviously, which directly leads to lower damage thresholds. The damage threshold increases as incident wavelength increases and the height of defect decreases. The reduction of damage threshold caused by defect decreases first and then increases with the pulse increasing. The damage threshold owns a minimum at 1.80 ps and 15.80 ps when the wavelength is respectively 351 nm and 1064 nm.
In order to study the effect of the defects on damage threshold of the surface, we modeled a classical three-dimension defect which is similar to the circular cone protuberance and calculated the electric field around this kind of defects by finite-difference method. Based on the field effect theory we calculated the damage thresholds of surfaces with different size defects. It can be got that the electric fields were amplified obviously, which directly leads to lower damage thresholds. The damage threshold increases as incident wavelength increases and the height of defect decreases. The reduction of damage threshold caused by defect decreases first and then increases with the pulse increasing. The damage threshold owns a minimum at 1.80 ps and 15.80 ps when the wavelength is respectively 351 nm and 1064 nm.
2015,
27: 062001.
doi: 10.11884/HPLPB201527.062001
Abstract:
In order to prepare the Mo/B4C multilayer mirrors in 7 nm, the stress and thermal stability mechanism in Mo/B4C multilayers with different annealing ways was studied. Firstly, the periodic Mo/B4C multilayers with 60 bilayers were deposited in the fused silica substrate and Si substrate by DC magnetron sputtering method, the design periodic thickness(D) is 3.58 nm, the ratio of the thickness of the Mo with D is 0.4. Secondly, the prepared samples were annealed with various annealing ways, the maximum annealing temperature was 500 ℃. Finally, the period, the interface roughness and stress were measured using X-ray grazing incidence reflection, X-ray scattering and optical interferometer before and after annealing, respectively. The test results show that the vacuum annealing method can effectively reduce the stress of Mo/B4C multilayers, and the period and interface roughness of the Mo/B4C multilayers have no significant changes, which prove the Mo/B4C multilayers have good thermal stability within 500 ℃.
In order to prepare the Mo/B4C multilayer mirrors in 7 nm, the stress and thermal stability mechanism in Mo/B4C multilayers with different annealing ways was studied. Firstly, the periodic Mo/B4C multilayers with 60 bilayers were deposited in the fused silica substrate and Si substrate by DC magnetron sputtering method, the design periodic thickness(D) is 3.58 nm, the ratio of the thickness of the Mo with D is 0.4. Secondly, the prepared samples were annealed with various annealing ways, the maximum annealing temperature was 500 ℃. Finally, the period, the interface roughness and stress were measured using X-ray grazing incidence reflection, X-ray scattering and optical interferometer before and after annealing, respectively. The test results show that the vacuum annealing method can effectively reduce the stress of Mo/B4C multilayers, and the period and interface roughness of the Mo/B4C multilayers have no significant changes, which prove the Mo/B4C multilayers have good thermal stability within 500 ℃.
2015,
27: 062002.
doi: 10.11884/HPLPB201527.062002
Abstract:
To fabricate well distributed dried gel precursor of titanium doped hollow glass microspheres (HGMs) by sol-gel method, titanium source and silicon source were pre-hydrolyzed separately and acetic acid was applied to control the hydrolysis of tetrabutyl titanate (TBOT). Effects of content of solvent, inhibitor and titanium on the stability and uniformity of sol and influences of aging and drying conditions and titanium concentration on the quality of gels were investigated. Besides, optimized conditions were obtained. Results show that acetic acid can control the hydrolysis of TBOT effectively and improve the stability of sol. With titanium source and silicon source pre-hydrolyzed separately, titanium doped sol precursors can be prepared under control. Stable and uniform sol can be obtained with mole ratio of anhydrous ethanol to alkoxides at 5, acetic acid to TBOT at 6 and atom ratio of Ti to Si (N (Ti)/N (Si)) from 2% to 20%. Sols with N (Ti)/ N (Si) less than 10% age at 100 ℃ for 24h and dry at 100 ℃ in open circumstance for 24 h convert to uniform gels. Sodium chloride separates from gels with N (Ti)/ N (Si) more than 10% during drying process, which reduces the uniformity of gels.
To fabricate well distributed dried gel precursor of titanium doped hollow glass microspheres (HGMs) by sol-gel method, titanium source and silicon source were pre-hydrolyzed separately and acetic acid was applied to control the hydrolysis of tetrabutyl titanate (TBOT). Effects of content of solvent, inhibitor and titanium on the stability and uniformity of sol and influences of aging and drying conditions and titanium concentration on the quality of gels were investigated. Besides, optimized conditions were obtained. Results show that acetic acid can control the hydrolysis of TBOT effectively and improve the stability of sol. With titanium source and silicon source pre-hydrolyzed separately, titanium doped sol precursors can be prepared under control. Stable and uniform sol can be obtained with mole ratio of anhydrous ethanol to alkoxides at 5, acetic acid to TBOT at 6 and atom ratio of Ti to Si (N (Ti)/N (Si)) from 2% to 20%. Sols with N (Ti)/ N (Si) less than 10% age at 100 ℃ for 24h and dry at 100 ℃ in open circumstance for 24 h convert to uniform gels. Sodium chloride separates from gels with N (Ti)/ N (Si) more than 10% during drying process, which reduces the uniformity of gels.
2015,
27: 062003.
doi: 10.11884/HPLPB201527.062003
Abstract:
To probe the electron density distribution of the plasma, double-frequency grating shearing interferometry based on the soft X-ray laser technology is developed. The 13.9 nm Ni-like Ag soft X-ray laser is used as a probe to make attempt on the diagnosis of laser produced plasma from a planar gold wafer target. Clear interference fringes image is achieved, which fully demonstrates the practicability of this technology. However, there are some problems such as the unclear target surface in the image. Analysis indicates the main reasons of these problems and a reasonable solution is proposed to improve this technology. Key words: diagnoses of plasma; interference technique; soft X-ray laser
To probe the electron density distribution of the plasma, double-frequency grating shearing interferometry based on the soft X-ray laser technology is developed. The 13.9 nm Ni-like Ag soft X-ray laser is used as a probe to make attempt on the diagnosis of laser produced plasma from a planar gold wafer target. Clear interference fringes image is achieved, which fully demonstrates the practicability of this technology. However, there are some problems such as the unclear target surface in the image. Analysis indicates the main reasons of these problems and a reasonable solution is proposed to improve this technology. Key words: diagnoses of plasma; interference technique; soft X-ray laser
2015,
27: 062004.
doi: 10.11884/HPLPB201527.062004
Abstract:
The rectangle diagnostic hole on the side of Au hohlraum was machined using electrical discharge machining milling (EDM-milling) by layer technology. The zone of the EDM was controled under the electrode and the side of the electrode was not machined. The size of diagnostic hole was characterized by OLYMPUS STM6 measuring microscope. The results indicate that the dimension precision of diagnostic hole is less than 5 m.
The rectangle diagnostic hole on the side of Au hohlraum was machined using electrical discharge machining milling (EDM-milling) by layer technology. The zone of the EDM was controled under the electrode and the side of the electrode was not machined. The size of diagnostic hole was characterized by OLYMPUS STM6 measuring microscope. The results indicate that the dimension precision of diagnostic hole is less than 5 m.
2015,
27: 062005.
doi: 10.11884/HPLPB201527.062005
Abstract:
In the inertial confinement fusion (ICF) experiment, down-scattered neutrons for fuel areal density measurement need to be separated from other background. The background on Shenguang Ⅲ facility is analyzed in detail by Monte Carlo for the DD fuel. As a result, the background is mostly from the process that primary neutrons scatter through vacuum chamber, surrounding diagnostic platforms, ceiling and floor. According to the analysis, appropriate materials and shielding solution are chosen. And the structure of the collimator is optimized by Monte Carlo. The design meets the experimental requirements.
In the inertial confinement fusion (ICF) experiment, down-scattered neutrons for fuel areal density measurement need to be separated from other background. The background on Shenguang Ⅲ facility is analyzed in detail by Monte Carlo for the DD fuel. As a result, the background is mostly from the process that primary neutrons scatter through vacuum chamber, surrounding diagnostic platforms, ceiling and floor. According to the analysis, appropriate materials and shielding solution are chosen. And the structure of the collimator is optimized by Monte Carlo. The design meets the experimental requirements.
2015,
27: 062006.
doi: 10.11884/HPLPB201527.062006
Abstract:
Low-density Au-doped poly(4-methyl-1-petene) (PMP) foams were successfully obtained via thermal induced phase inversion method using PMP as the foam skeleton materials, gold particles as doping materials, and naphthalene and 1,2,4,5-tetramethylbenzene as mixed solvent. The results showed that the actual density is linear with the theoretical density of Au-doped foams as the theoretical Au mass fraction is fixed. The actual Au mass fraction is lower than the theoretical Au mass fraction. Au-doped PMP foams and pure PMP foams are similar in porous morphologies, and the increased Au mass fraction leads to the increased pore size distribution and interconnected skeleton size.
Low-density Au-doped poly(4-methyl-1-petene) (PMP) foams were successfully obtained via thermal induced phase inversion method using PMP as the foam skeleton materials, gold particles as doping materials, and naphthalene and 1,2,4,5-tetramethylbenzene as mixed solvent. The results showed that the actual density is linear with the theoretical density of Au-doped foams as the theoretical Au mass fraction is fixed. The actual Au mass fraction is lower than the theoretical Au mass fraction. Au-doped PMP foams and pure PMP foams are similar in porous morphologies, and the increased Au mass fraction leads to the increased pore size distribution and interconnected skeleton size.
2015,
27: 062007.
doi: 10.11884/HPLPB201527.062007
Abstract:
To investigate the influence of the radiation heat transfer on cryogenic target system, a computational fluid dynamics model for cryogenic target with a radiation shield is established. The modeling is implemented with FLUENT software, and the discrete ordinates model is adopted for calculating radiation heat transfer. The structure and parameters participating in radiation heat transfer are analyzed. The results show that the following measures help to reduce the radiation heat transfer and improve the temperature unity around the target: using double radiation shield, decreasing the emissivity of the radiation shield, increasing the diffusion fraction of the radiation shield, increasing the absorptivity of the hohlraum, and adding storm windows.
To investigate the influence of the radiation heat transfer on cryogenic target system, a computational fluid dynamics model for cryogenic target with a radiation shield is established. The modeling is implemented with FLUENT software, and the discrete ordinates model is adopted for calculating radiation heat transfer. The structure and parameters participating in radiation heat transfer are analyzed. The results show that the following measures help to reduce the radiation heat transfer and improve the temperature unity around the target: using double radiation shield, decreasing the emissivity of the radiation shield, increasing the diffusion fraction of the radiation shield, increasing the absorptivity of the hohlraum, and adding storm windows.
2015,
27: 062008.
doi: 10.11884/HPLPB201527.062008
Abstract:
A preparation method of hollow glass microsphere (HGM) is investigated, which adopts glow discharge polymerization technology and uses tetramethyl silane (TMS) as the dopant gas, in order to control the diameter and thickness of hollow glass microspheres for inertial confinement fusion targets. The results show that 5% silicon in Si-GDP shells is a compromised concentration for fabricating HGM whose diameter is 400-600 m and thickness is 5-15 m. We can successfully control the shrinkage of the diameter and wall thickness at about 38%. The carbon concentration of the samples decreases significantly and it mainly exists in the form of CSi bonding, while the silicon concentration increases significantly and it mainly exists in the form of SiO bonding after the sintering step. The residual pressure reaches 72.95% in the shells which filled 1.23 MPa deuterium after 96 h.
A preparation method of hollow glass microsphere (HGM) is investigated, which adopts glow discharge polymerization technology and uses tetramethyl silane (TMS) as the dopant gas, in order to control the diameter and thickness of hollow glass microspheres for inertial confinement fusion targets. The results show that 5% silicon in Si-GDP shells is a compromised concentration for fabricating HGM whose diameter is 400-600 m and thickness is 5-15 m. We can successfully control the shrinkage of the diameter and wall thickness at about 38%. The carbon concentration of the samples decreases significantly and it mainly exists in the form of CSi bonding, while the silicon concentration increases significantly and it mainly exists in the form of SiO bonding after the sintering step. The residual pressure reaches 72.95% in the shells which filled 1.23 MPa deuterium after 96 h.
2015,
27: 062009.
doi: 10.11884/HPLPB201527.062009
Abstract:
The cryogenic target is an important target type to achieve high inertial confinement fusion energy gain. The cooling arm connected the cool source to the aluminum sleeve is an important part of the cryogenic target, which is used to obtain accurate temperature field for the deuterium-tritium ice pellet, and uniformly clamp the aluminum sleeve. First the thermal conductivity of silicon material was measured，and the experiment shows that the silicon material has excellent thermal conductivity under the cryogenic temperature. Then the influences of structural parameters of the silicon cooling arm on the temperature field were analyzed. The impacts of different crystal orientation silicon cooling arm were studied, and the (111)silicon was chosen to fabricate cooling arm for its unique circumferentially uniform clamping force. The analyses of the clamping force, resonance frequency and the thermal-structure coupling analysis of the cooling arm were given. After that, the structure design of the cooling arm with two-level branch structure and 16 clamping fingers was proposed. Then the process of the cooling arm was designed based on MEMS technology and the prototype of cooling arm was realized. The vertical sidewall and mechanical properties of the cooling arm were measured. Finally the assembly sample of cooling arm with an aluminum sleeve was given, which indicated that the cooling arm can be achieved on clamping the sleeve.
The cryogenic target is an important target type to achieve high inertial confinement fusion energy gain. The cooling arm connected the cool source to the aluminum sleeve is an important part of the cryogenic target, which is used to obtain accurate temperature field for the deuterium-tritium ice pellet, and uniformly clamp the aluminum sleeve. First the thermal conductivity of silicon material was measured，and the experiment shows that the silicon material has excellent thermal conductivity under the cryogenic temperature. Then the influences of structural parameters of the silicon cooling arm on the temperature field were analyzed. The impacts of different crystal orientation silicon cooling arm were studied, and the (111)silicon was chosen to fabricate cooling arm for its unique circumferentially uniform clamping force. The analyses of the clamping force, resonance frequency and the thermal-structure coupling analysis of the cooling arm were given. After that, the structure design of the cooling arm with two-level branch structure and 16 clamping fingers was proposed. Then the process of the cooling arm was designed based on MEMS technology and the prototype of cooling arm was realized. The vertical sidewall and mechanical properties of the cooling arm were measured. Finally the assembly sample of cooling arm with an aluminum sleeve was given, which indicated that the cooling arm can be achieved on clamping the sleeve.
2015,
27: 062010.
doi: 10.11884/HPLPB201527.062010
Abstract:
The transmitted wave front aberration is the key factor which restricts the further development of high average power solid-state lasers. This work analyses the error source of transmitted wave front for end surface, and a scheme of slab processing is purposed according to technology requirement of Nd:YAG crystal slab for high average power solid-state lasers. With the new type complex pad, fixture of slab and new polishing process, the problem of poor controllability of surface figure and wedge angle in continuous polishing has been solved. The processing results show that the PV of end surface transmitted wavefront aberration reached 0.74 for 150 mm30 mm2.5 mm specification Nd:YAG crystal slab. The processing precision satisfies the application requirement of high average power solid-state lasers.
The transmitted wave front aberration is the key factor which restricts the further development of high average power solid-state lasers. This work analyses the error source of transmitted wave front for end surface, and a scheme of slab processing is purposed according to technology requirement of Nd:YAG crystal slab for high average power solid-state lasers. With the new type complex pad, fixture of slab and new polishing process, the problem of poor controllability of surface figure and wedge angle in continuous polishing has been solved. The processing results show that the PV of end surface transmitted wavefront aberration reached 0.74 for 150 mm30 mm2.5 mm specification Nd:YAG crystal slab. The processing precision satisfies the application requirement of high average power solid-state lasers.
Influence of photoelectron energy and angular distribution and space charge effect on streak cameras
2015,
27: 062011.
doi: 10.11884/HPLPB201527.062011
Abstract:
Based on study of femtosecond streak camera system and femtosecond electron diffraction system, the influence of photoelectron energy, angular distribution and space charge effect on photoelectron time and energy spread in photocathode-mesh acceleration region is analyzed using Monte Carlo simulation. When the ultraviolet and soft X-ray incident photocathode, the time spread values of six types of photoelectron initial energy distribution is given. The relationship of electronic time spread between emission current density and accelerating field is analyzed. Electrons redistribute themselves inside the pulse, a linear velocity chirp develops on the electron pulse in acceleration region, the energy dispersion changes differently from that in free propagation region. The analysis and findings are useful for the study of ultrafast electronic propagation dynamics and the design of femtosecond streak camera, femtosecond electron diffraction and energy compensation components.
Based on study of femtosecond streak camera system and femtosecond electron diffraction system, the influence of photoelectron energy, angular distribution and space charge effect on photoelectron time and energy spread in photocathode-mesh acceleration region is analyzed using Monte Carlo simulation. When the ultraviolet and soft X-ray incident photocathode, the time spread values of six types of photoelectron initial energy distribution is given. The relationship of electronic time spread between emission current density and accelerating field is analyzed. Electrons redistribute themselves inside the pulse, a linear velocity chirp develops on the electron pulse in acceleration region, the energy dispersion changes differently from that in free propagation region. The analysis and findings are useful for the study of ultrafast electronic propagation dynamics and the design of femtosecond streak camera, femtosecond electron diffraction and energy compensation components.
2015,
27: 063001.
doi: 10.11884/HPLPB201527.063001
Abstract:
In order to explore the technology of high power microwave(HPM) generation by ultra short electrical pulse supply, the technical feasibility of generating wide spectrum HPM was analyzed by an S band relativistic extended interaction cavity oscillator(REICO) driven by ultra short electrical pulse using the theory and particle simulation method. A principle experiment using the Marx generator to generate triangle narrow electrical pulse driving the S band REICO was carried out. The rising time of 15 ns, along 30 ns, voltage 560 kV, current 2.8 kA triangle electron beam pulse produced by the Marx generator drove the REICO, and it produced short pulse high power microwave with a power of 410 MW, a pulse width of 8 ns, and a relative instantaneous bandwidth of 2.7% in simulation. Correspondingly, it generated the output microwave power of 160 MW, pulse width 10 ns, center frequency of 2.75 GHz, the relative bandwidth of 2.8% in the experiment.
In order to explore the technology of high power microwave(HPM) generation by ultra short electrical pulse supply, the technical feasibility of generating wide spectrum HPM was analyzed by an S band relativistic extended interaction cavity oscillator(REICO) driven by ultra short electrical pulse using the theory and particle simulation method. A principle experiment using the Marx generator to generate triangle narrow electrical pulse driving the S band REICO was carried out. The rising time of 15 ns, along 30 ns, voltage 560 kV, current 2.8 kA triangle electron beam pulse produced by the Marx generator drove the REICO, and it produced short pulse high power microwave with a power of 410 MW, a pulse width of 8 ns, and a relative instantaneous bandwidth of 2.7% in simulation. Correspondingly, it generated the output microwave power of 160 MW, pulse width 10 ns, center frequency of 2.75 GHz, the relative bandwidth of 2.8% in the experiment.
2015,
27: 063002.
doi: 10.11884/HPLPB201527.063002
Abstract:
This paper describes the design of an array antenna which can generate radio waves carrying orbital angular momentum (OAM) at 6 GHz. We consider the microstrip antenna with coaxial feed as the element to compose the circular antenna array which is excited with unit amplitude but with phase delay from element to element. According to the simulation and optimization with high frequency structure simulator(HFSS), we get different patterns of OAM modes depending on the different phase delay, and obtain the vortex electromagnetic wave carrying orbital angular momentum.
This paper describes the design of an array antenna which can generate radio waves carrying orbital angular momentum (OAM) at 6 GHz. We consider the microstrip antenna with coaxial feed as the element to compose the circular antenna array which is excited with unit amplitude but with phase delay from element to element. According to the simulation and optimization with high frequency structure simulator(HFSS), we get different patterns of OAM modes depending on the different phase delay, and obtain the vortex electromagnetic wave carrying orbital angular momentum.
2015,
27: 063003.
doi: 10.11884/HPLPB201527.063003
Abstract:
The phase shifter is a key part of high power phased antenna arrays whose beam of radiation can be steered. A high power rectangular waveguide phase shifter was designed. A metal piece is inserted into the waveguide paralleled with the narrow sidewall of the rectangular waveguide. The metal piece brings an agitation of the electromagnetic field in the waveguide. Moving the metal piece in the waveguide along the wide sidewall direction leads to continuous shifting of phase. 0-360 phase shifting can be obtained by optimization of the structure of waveguide and metal piece. Low insertion loss can be achieved by optimization of structure of metal piece. The phase shifter is completely metallic, so that it can hold high power microwave transmission. The operating frequency of the phase shifter is 9.4 GHz, and the length is 30 cm. The max shifting phase is 360, the max insertion loss is less than 0.2 dB, the power handling capabilities of the shifter is more than 64 MW. The measured insertion loss is less than 0.5 dB, and the measured phase versus frequency is linear.
The phase shifter is a key part of high power phased antenna arrays whose beam of radiation can be steered. A high power rectangular waveguide phase shifter was designed. A metal piece is inserted into the waveguide paralleled with the narrow sidewall of the rectangular waveguide. The metal piece brings an agitation of the electromagnetic field in the waveguide. Moving the metal piece in the waveguide along the wide sidewall direction leads to continuous shifting of phase. 0-360 phase shifting can be obtained by optimization of the structure of waveguide and metal piece. Low insertion loss can be achieved by optimization of structure of metal piece. The phase shifter is completely metallic, so that it can hold high power microwave transmission. The operating frequency of the phase shifter is 9.4 GHz, and the length is 30 cm. The max shifting phase is 360, the max insertion loss is less than 0.2 dB, the power handling capabilities of the shifter is more than 64 MW. The measured insertion loss is less than 0.5 dB, and the measured phase versus frequency is linear.
2015,
27: 063004.
doi: 10.11884/HPLPB201527.063004
Abstract:
A metallic photonic crystal TEM-TE11 mode converter is designed and its testing results are presented. Simulation results show that its conversion efficiency is above 99% at the center frequency of 1.31 GHz. In the frequency range of 1.27-1.376 GHz, the conversion efficiency exceeds 90%, with a corresponding bandwidth of 8.1%. A TEM mode excitation and a horn antenna are fabricated to test the performance of the mode converter. The mode converter is also tested with a magnetically insulated transmission line oscillator (MILO) tube. The whole device works well. The photonic TEM-TE11 mode converter is capable of handling GW level high power microwave. The measured radiation patterns of the mode converter agree well with the simulated results, indicating that the simulated results are valid.
A metallic photonic crystal TEM-TE11 mode converter is designed and its testing results are presented. Simulation results show that its conversion efficiency is above 99% at the center frequency of 1.31 GHz. In the frequency range of 1.27-1.376 GHz, the conversion efficiency exceeds 90%, with a corresponding bandwidth of 8.1%. A TEM mode excitation and a horn antenna are fabricated to test the performance of the mode converter. The mode converter is also tested with a magnetically insulated transmission line oscillator (MILO) tube. The whole device works well. The photonic TEM-TE11 mode converter is capable of handling GW level high power microwave. The measured radiation patterns of the mode converter agree well with the simulated results, indicating that the simulated results are valid.
2015,
27: 063201.
doi: 10.11884/HPLPB201527.063201
Abstract:
Based on traditional shooting and bouncing rays (SBR), the ray-tracing procedure and intersection tests were improved for the flat surface scatterers. Combined with SBR, a fast method of ray/triangle intersection was studied. The surface of the targets was subdivided by triangles twice, obtaining low density of triangles used for intersection tests and high density of triangles used for ray tracing as the original ray tubes. After ray-tracing program, the electromagnetic scattering problem could be solved by physical optics (PO) integration. The results of the proposed method were compared with those in the references. The good agreement between the results proved the preciseness of this method. And the efficiency of the method was proved by the results of different densities of subdivisions.
Based on traditional shooting and bouncing rays (SBR), the ray-tracing procedure and intersection tests were improved for the flat surface scatterers. Combined with SBR, a fast method of ray/triangle intersection was studied. The surface of the targets was subdivided by triangles twice, obtaining low density of triangles used for intersection tests and high density of triangles used for ray tracing as the original ray tubes. After ray-tracing program, the electromagnetic scattering problem could be solved by physical optics (PO) integration. The results of the proposed method were compared with those in the references. The good agreement between the results proved the preciseness of this method. And the efficiency of the method was proved by the results of different densities of subdivisions.
2015,
27: 063202.
doi: 10.11884/HPLPB201527.063202
Abstract:
The propagation properties of large size TEM antennas are experimentally studied. The size of the TEM antennas is 60 m20 m10 m and the character impedance is 120 . A kind of dielectric foil switch is designed compactly with TEM antennas which can generate a double exponential waveform with an altitude of 10 kV and a rise time of 1.2 ns. The radiated field distribution is measured. The relationship between the rise time/altitude and the distance is provided, and the propagation properties of large size TEM antennas are summarized. The results show that the rise time along the transmission distance increases. The transmission distance is 50 m and the rise time increases about 1.2 ns. An exponential decay trend of electric field amplitude with the transmission distance. This work is valuable for the design of large size guided wave simulator.
The propagation properties of large size TEM antennas are experimentally studied. The size of the TEM antennas is 60 m20 m10 m and the character impedance is 120 . A kind of dielectric foil switch is designed compactly with TEM antennas which can generate a double exponential waveform with an altitude of 10 kV and a rise time of 1.2 ns. The radiated field distribution is measured. The relationship between the rise time/altitude and the distance is provided, and the propagation properties of large size TEM antennas are summarized. The results show that the rise time along the transmission distance increases. The transmission distance is 50 m and the rise time increases about 1.2 ns. An exponential decay trend of electric field amplitude with the transmission distance. This work is valuable for the design of large size guided wave simulator.
2015,
27: 064001.
doi: 10.11884/HPLPB201527.064001
Abstract:
The effects of X-ray scattering on areal density measurement results and an expression of measurement results deviation are obtained with a qualitative analysis. The effects at different photographic layout, energy sources and material types are studied using Monte-Carlo method. The simulation results show that without protective windows, the scattering from the object would reduce the measurement results; with protective windows, the front window scattering has little effects on the measurement results, and the effects of back window scattering are related to the sample-scintillator distance, the shorter the distance is, the greater the effects are; in a certain energy range, the lower the energy of photon is, the larger the measurement result error is; the bigger the atomic number and density of the object are, the larger the measurement result error is.
The effects of X-ray scattering on areal density measurement results and an expression of measurement results deviation are obtained with a qualitative analysis. The effects at different photographic layout, energy sources and material types are studied using Monte-Carlo method. The simulation results show that without protective windows, the scattering from the object would reduce the measurement results; with protective windows, the front window scattering has little effects on the measurement results, and the effects of back window scattering are related to the sample-scintillator distance, the shorter the distance is, the greater the effects are; in a certain energy range, the lower the energy of photon is, the larger the measurement result error is; the bigger the atomic number and density of the object are, the larger the measurement result error is.
2015,
27: 064002.
doi: 10.11884/HPLPB201527.064002
Abstract:
Numerical simulation method could be used to investigate the possibility and effectiveness of phase contrast imaging for certain testing objects, moreover, to optimize imaging parameters. For X-ray in-line phase-contrast imaging system, principle of numerical simulation and the implementation method were analyzed first, and simulation for testing objects with round shape and strip shape were carried out afterward. After comparison of the simulation results, we know that the discretization size of testing object affects, to a large extent, the accuracy of numerical simulation results. The reason is that the accuracy of optical transform function (OTF) in the phase contrast imaging is determined by the discretization size of testing object. To guarantee the accuracy of simulation results, we should ensure no evident distortions exist in discretization of OTF and the discretization points are continuous. For an accurate simulation, the discrete size of OTF is not fixed, which should match the size of the testing object.
Numerical simulation method could be used to investigate the possibility and effectiveness of phase contrast imaging for certain testing objects, moreover, to optimize imaging parameters. For X-ray in-line phase-contrast imaging system, principle of numerical simulation and the implementation method were analyzed first, and simulation for testing objects with round shape and strip shape were carried out afterward. After comparison of the simulation results, we know that the discretization size of testing object affects, to a large extent, the accuracy of numerical simulation results. The reason is that the accuracy of optical transform function (OTF) in the phase contrast imaging is determined by the discretization size of testing object. To guarantee the accuracy of simulation results, we should ensure no evident distortions exist in discretization of OTF and the discretization points are continuous. For an accurate simulation, the discrete size of OTF is not fixed, which should match the size of the testing object.
2015,
27: 064101.
doi: 10.11884/HPLPB201527.064101
Abstract:
An optimization algorithm based on stitching for two segments of surface figure is proposed to solve the problem that the stitching measuring of lare-aperture asphere lacks accuracy during grinding process. Firstly, the preliminary stitching model for two segments of surface profile is built. Secondly, the effect of motion ( and L) and motion error ( and L) are analysed using 350 mm workpiece stitch simulation. Simulation results indicate stitching errors increase as translation errors increase and the standard deviations of stitching errors are 0.2 m when translation is under 10 mm, and the rotation is under 8, and the rotation error is under 60 and the translation error is under 3 m. Finally, Talysurf PGI 1240 and stitching fixture are used to test 120 mm aspheric optical element and analyse the effect of different motion. Experimental results indicate the standard deviations of stitching errors are 0.2-0.6 m when translation is under 10 mm and the rotation is under 8. It can satisfy the measuring requirements of surface profile in optical elements during grinding process.
An optimization algorithm based on stitching for two segments of surface figure is proposed to solve the problem that the stitching measuring of lare-aperture asphere lacks accuracy during grinding process. Firstly, the preliminary stitching model for two segments of surface profile is built. Secondly, the effect of motion ( and L) and motion error ( and L) are analysed using 350 mm workpiece stitch simulation. Simulation results indicate stitching errors increase as translation errors increase and the standard deviations of stitching errors are 0.2 m when translation is under 10 mm, and the rotation is under 8, and the rotation error is under 60 and the translation error is under 3 m. Finally, Talysurf PGI 1240 and stitching fixture are used to test 120 mm aspheric optical element and analyse the effect of different motion. Experimental results indicate the standard deviations of stitching errors are 0.2-0.6 m when translation is under 10 mm and the rotation is under 8. It can satisfy the measuring requirements of surface profile in optical elements during grinding process.
2015,
27: 064102.
doi: 10.11884/HPLPB201527.064102
Abstract:
The free-standing nanoporous gold film was synthesized by free corrosion dealloying in the increasing HNO3 solution. Au-Ag precursors was preparated by alloying the Au and Ag film of the magnetron sputtered. Micro-structure and composition of the sample before and after dealloying were characterized with scanning electron microscope and energy dispersive analysis of X-ray. The results indicated that the Au-Ag alloy precursors were obtained by 400 ℃ heat-treatment for 36 h. The increasing HNO3 solution prevented the surface to crack. The self-supported nanoporous gold with size up to 15mm15 mm, thickness of 400-500 nm, ligament size of 40-40 nm, porosity of 56% were obtained.
The free-standing nanoporous gold film was synthesized by free corrosion dealloying in the increasing HNO3 solution. Au-Ag precursors was preparated by alloying the Au and Ag film of the magnetron sputtered. Micro-structure and composition of the sample before and after dealloying were characterized with scanning electron microscope and energy dispersive analysis of X-ray. The results indicated that the Au-Ag alloy precursors were obtained by 400 ℃ heat-treatment for 36 h. The increasing HNO3 solution prevented the surface to crack. The self-supported nanoporous gold with size up to 15mm15 mm, thickness of 400-500 nm, ligament size of 40-40 nm, porosity of 56% were obtained.
2015,
27: 064103.
doi: 10.11884/HPLPB201527.064103
Abstract:
To develop a trigger switch for application in the exploding foil initiator, a one-shot switch of sandwich structure with Parylene C film as dielectric layer was fabricated based on micro-fabrication technology. In the experiments, the characteristics of the switch were analyzed by applying a main voltage varying from 1.0 kV to 1.6 kV. The results show that the peak current is 1020 A and the rise time is about 240 ns when the applied voltage reaches 1.4 kV. The performance of the one-shot switch based on Parylene C is better than that based on Polyimide. The peak current shows an increasing trend with increasing the loaded voltage while the rise time is almost the same. The delay time distributes randomly between 1s and 200 s. The experimental simulation results show that the switch resistance increases with time.
To develop a trigger switch for application in the exploding foil initiator, a one-shot switch of sandwich structure with Parylene C film as dielectric layer was fabricated based on micro-fabrication technology. In the experiments, the characteristics of the switch were analyzed by applying a main voltage varying from 1.0 kV to 1.6 kV. The results show that the peak current is 1020 A and the rise time is about 240 ns when the applied voltage reaches 1.4 kV. The performance of the one-shot switch based on Parylene C is better than that based on Polyimide. The peak current shows an increasing trend with increasing the loaded voltage while the rise time is almost the same. The delay time distributes randomly between 1s and 200 s. The experimental simulation results show that the switch resistance increases with time.
2015,
27: 064104.
doi: 10.11884/HPLPB201527.064104
Abstract:
This paper aims at optimizing the diamond tool trajectory in ultra-precision machining of perturbation surface with single point diamond turning technology. First, the ultra-precision machining principle of multi-mode sine surface is illustrated. Second, the parallel chord bi-arc interpolating algorithm is theoretically analyzed, of which the interpolating trajectory error expression is obtained. On this basis, the parallel chord bi-arc interpolating algorithm with adaptive step length is introduced for dynamically controlling the interpolating trajectory error. And the interpolation formula is derived. Finally, the new interpolating algorithm is adopted for example analyzing with Matlab software, and is compared with two other algorithms, the linear interpolation and the parallel chord bi-arc interpolation with fixed step length. The simulation results present that the new algorithm can maximally reduce interpolating sections in conditions of trajectory error, which helps to improve the machining efficiency and extend the cutting life span.
This paper aims at optimizing the diamond tool trajectory in ultra-precision machining of perturbation surface with single point diamond turning technology. First, the ultra-precision machining principle of multi-mode sine surface is illustrated. Second, the parallel chord bi-arc interpolating algorithm is theoretically analyzed, of which the interpolating trajectory error expression is obtained. On this basis, the parallel chord bi-arc interpolating algorithm with adaptive step length is introduced for dynamically controlling the interpolating trajectory error. And the interpolation formula is derived. Finally, the new interpolating algorithm is adopted for example analyzing with Matlab software, and is compared with two other algorithms, the linear interpolation and the parallel chord bi-arc interpolation with fixed step length. The simulation results present that the new algorithm can maximally reduce interpolating sections in conditions of trajectory error, which helps to improve the machining efficiency and extend the cutting life span.
2015,
27: 064105.
doi: 10.11884/HPLPB201527.064105
Abstract:
Based on the self-consistent system of the quantum hydrodynamic equations and dust grains charging equation for electron-ion-dust plasmas, and taking into account the quantum effects of the electrons and ions, we studied the influences of dust grains charging on dust acoustic waves in the quantum dusty plasmas. To derive and study a dispersion relation for a dust mode we applied the linear theory analysis method and used numerical simulation. It is found that the dispersion characteristics of dust acoustic waves are qualitatively modified by the charging effect, leading to the dissipation of dust acoustic waves. The dissipation strength mainly depends on the dust plasma parameters. Finally, the physical cause of the dissipation is analyzed.
Based on the self-consistent system of the quantum hydrodynamic equations and dust grains charging equation for electron-ion-dust plasmas, and taking into account the quantum effects of the electrons and ions, we studied the influences of dust grains charging on dust acoustic waves in the quantum dusty plasmas. To derive and study a dispersion relation for a dust mode we applied the linear theory analysis method and used numerical simulation. It is found that the dispersion characteristics of dust acoustic waves are qualitatively modified by the charging effect, leading to the dissipation of dust acoustic waves. The dissipation strength mainly depends on the dust plasma parameters. Finally, the physical cause of the dissipation is analyzed.
2015,
27: 065001.
doi: 10.11884/HPLPB201527.065001
Abstract:
Magnetic sawing phenomenon, induced by the crack in the rail of the electromagnetic launcher, can severely restrict the life of the launcher. To analyze this phenomenon, we built the magnetic field diffusion equation and heat conduction equation. Combined with the solid mechanics model in the finite element software COMSOL Multiphysics, we simulated the electromagnetic, thermal and mechanical behaviors of the crack. The results show that the current-crowding as the current path turns around the crack tip is a key factor for the formation of magnetic sawing phenomenon. Moreover, we found that, the smaller the aperture angle, the higher the current density, the faster temperature rises.
Magnetic sawing phenomenon, induced by the crack in the rail of the electromagnetic launcher, can severely restrict the life of the launcher. To analyze this phenomenon, we built the magnetic field diffusion equation and heat conduction equation. Combined with the solid mechanics model in the finite element software COMSOL Multiphysics, we simulated the electromagnetic, thermal and mechanical behaviors of the crack. The results show that the current-crowding as the current path turns around the crack tip is a key factor for the formation of magnetic sawing phenomenon. Moreover, we found that, the smaller the aperture angle, the higher the current density, the faster temperature rises.
2015,
27: 065003.
doi: 10.11884/HPLPB201527.065003
Abstract:
A high power short pulse can be generated by using pulse compression technology. The high impedance pulse forming line is initially charged, when its switch is closed, the energy flows to the lower impedance pulse forming line, as the voltage builds on the lower impedance pulse forming line, the output switch closes and the high power short pulse is generated and delivered to the output transmission line section. The principle analysis of pulse compression is presented. A GW level ns pulse driver is used as the high impedance pulse forming line with a characteristic impedance of 40 , an electrical length of 3.9 ns and an output pulse width of about 8 ns. The pulse compression device and impedance tapered line are developed, considering breakdown restrictions of lower impedance pulse forming line insulation and the output switch, the characteristic impedance and electrical length of pulse compression device are chosen as 6.5 and 0.5 ns respectively. By using the GW level nanosecond pulse driver, a pulse compression experiment is carried out. The experimental results show the pulse compression device output high power short pulse width is of 1.5 ns, and the power increase ratio is about 4, the experimental results are in good agreement with that from theoretical design.
A high power short pulse can be generated by using pulse compression technology. The high impedance pulse forming line is initially charged, when its switch is closed, the energy flows to the lower impedance pulse forming line, as the voltage builds on the lower impedance pulse forming line, the output switch closes and the high power short pulse is generated and delivered to the output transmission line section. The principle analysis of pulse compression is presented. A GW level ns pulse driver is used as the high impedance pulse forming line with a characteristic impedance of 40 , an electrical length of 3.9 ns and an output pulse width of about 8 ns. The pulse compression device and impedance tapered line are developed, considering breakdown restrictions of lower impedance pulse forming line insulation and the output switch, the characteristic impedance and electrical length of pulse compression device are chosen as 6.5 and 0.5 ns respectively. By using the GW level nanosecond pulse driver, a pulse compression experiment is carried out. The experimental results show the pulse compression device output high power short pulse width is of 1.5 ns, and the power increase ratio is about 4, the experimental results are in good agreement with that from theoretical design.
2015,
27: 065004.
doi: 10.11884/HPLPB201527.065004
Abstract:
Three types of electrode structures with typical electric field distribution are designed based on 600 kV SF6 trigatron switch. The breakdown characteristics of each structure are obtained on -600 kV / 400 ns pulse generator. With analyzing electric field uniformity of each structure, it is shown that the trigger breakdown mode of the planar electrode is related to the switch work ratio, and this structure has a small trigger jitter. Spherical electrodes jitter of selfbreakdown voltage is little, and it can stably work under longtime trigger breakdown mode. Conical electrode has a very unstable trigger mode, it is possibly because of is likely to be the close breakdown characteristics of the two gaps.
Three types of electrode structures with typical electric field distribution are designed based on 600 kV SF6 trigatron switch. The breakdown characteristics of each structure are obtained on -600 kV / 400 ns pulse generator. With analyzing electric field uniformity of each structure, it is shown that the trigger breakdown mode of the planar electrode is related to the switch work ratio, and this structure has a small trigger jitter. Spherical electrodes jitter of selfbreakdown voltage is little, and it can stably work under longtime trigger breakdown mode. Conical electrode has a very unstable trigger mode, it is possibly because of is likely to be the close breakdown characteristics of the two gaps.
2015,
27: 065005.
doi: 10.11884/HPLPB201527.065005
Abstract:
A 150 kV pulsed X-ray test system is designed according to the principle of bipolar charged Marx generator. It is mainly used for ballistics studies, impact studies and fluid dynamics simulation of weapons in flash photography. A 15-stage Marx generator is designed in coaxial structure and used in the pulse generator to shorten the pulse width of output pulses. Marx generator connects with the flash X-ray tube through a high-voltage cable. For a charging voltage of 20 kV per stage, the Marx generator generates a more than 150 kV pulse voltage that is applied to the X-ray tube. The X-ray tube generates a dose 7.810-6 C/kg at 0.25 m away for flash X-radiography with a pulse width of 60 ns. The size of X-ray source is 2.5 mm. 150 kV pulsed X-ray test system used with computed radiographic system be able to an imaging area of up to 30 cm40 cm, resolution is greater than 1 lp/mm for X-ray image . It is the ideal tool for high-speed radiation photography.
A 150 kV pulsed X-ray test system is designed according to the principle of bipolar charged Marx generator. It is mainly used for ballistics studies, impact studies and fluid dynamics simulation of weapons in flash photography. A 15-stage Marx generator is designed in coaxial structure and used in the pulse generator to shorten the pulse width of output pulses. Marx generator connects with the flash X-ray tube through a high-voltage cable. For a charging voltage of 20 kV per stage, the Marx generator generates a more than 150 kV pulse voltage that is applied to the X-ray tube. The X-ray tube generates a dose 7.810-6 C/kg at 0.25 m away for flash X-radiography with a pulse width of 60 ns. The size of X-ray source is 2.5 mm. 150 kV pulsed X-ray test system used with computed radiographic system be able to an imaging area of up to 30 cm40 cm, resolution is greater than 1 lp/mm for X-ray image . It is the ideal tool for high-speed radiation photography.
2015,
27: 065101.
doi: 10.11884/HPLPB201527.065101
Abstract:
Ion back bombardment is believed to be a major cause of degradation of the quantum efficiency (QE) of the photocathode in direct current(DC) high voltage guns and will reduce the operational lifetime of the cathode. With particle tracking and QE mapping, the effects and limitations of the beam off-axis emission to suppress the ions striking the photo-emission region are studied. The simulation results suggest that the ions mainly bombard the electrostatic center (EC) and the flux of ions near the location of beam emission is reduced by 95% with the beam off-axis emission. The QE maps on the cathode before and after the DC gun operation with CW beam demonstrate that the QE decays seriously within a large region near the EC and the QE degradation in the photo-emission region is suppressed by the beam off-axis emission. However, the off-axis emission will also degrade the beam quality. With an off-axis emission of 6 mm from the EC, the simulation results show that the transverse emittance is increased by about 4mmmrad.
Ion back bombardment is believed to be a major cause of degradation of the quantum efficiency (QE) of the photocathode in direct current(DC) high voltage guns and will reduce the operational lifetime of the cathode. With particle tracking and QE mapping, the effects and limitations of the beam off-axis emission to suppress the ions striking the photo-emission region are studied. The simulation results suggest that the ions mainly bombard the electrostatic center (EC) and the flux of ions near the location of beam emission is reduced by 95% with the beam off-axis emission. The QE maps on the cathode before and after the DC gun operation with CW beam demonstrate that the QE decays seriously within a large region near the EC and the QE degradation in the photo-emission region is suppressed by the beam off-axis emission. However, the off-axis emission will also degrade the beam quality. With an off-axis emission of 6 mm from the EC, the simulation results show that the transverse emittance is increased by about 4mmmrad.
2015,
27: 065102.
doi: 10.11884/HPLPB201527.065102
Abstract:
Abunch-by-bunch beam measurement system is developed for BEPCⅡ (Beijing Electron-Positron ColliderⅡ). In order to realize the bunch-by-bunch measurement, high isolation for signals of each bunch should be reached. The analogy signals are sampled bunch-by-bunch with high speed (500 MHz) ADCs. Bunch signals separation and digital processing are done in Field Programmable Gate Array (FPGA). A resolution of about 4.5 m for bunch-by-bunch measurement is reached. Bunch-by-bunch tunes and oscillation amplitudes are provided by the system. The system has become a powerful tool for BEPCⅡ machine study.
Abunch-by-bunch beam measurement system is developed for BEPCⅡ (Beijing Electron-Positron ColliderⅡ). In order to realize the bunch-by-bunch measurement, high isolation for signals of each bunch should be reached. The analogy signals are sampled bunch-by-bunch with high speed (500 MHz) ADCs. Bunch signals separation and digital processing are done in Field Programmable Gate Array (FPGA). A resolution of about 4.5 m for bunch-by-bunch measurement is reached. Bunch-by-bunch tunes and oscillation amplitudes are provided by the system. The system has become a powerful tool for BEPCⅡ machine study.
2015,
27: 065103.
doi: 10.11884/HPLPB201527.065103
Abstract:
A laser-wire scanner which can measure the transverse charge profiles of an electron (or positron) beam has been constructed at the Beijing Electron-Positron ColliderⅡ(BEPC Ⅱ) accelerator transport line in IHEP. The development of the system is explained in this paper, along with descriptions of its photon detector and laser system. Results of GEANT4 simulation about the process of interaction between laser photons and electron, Cerenkov radiation in different medium are presented. The parameters of the laser pulse such as width, size and power are measured. Laser optical system and mechanical scanning system are designed and tested. The Cherenkov detector is set up for detecting the Compton photons. Mathematical processing methods of laser scanner are given. Measurement results show the laser transport and focus subsystem work in accordance with the design, and the stability of laser focus parameters can meet the requirement of beam profile measurement.
A laser-wire scanner which can measure the transverse charge profiles of an electron (or positron) beam has been constructed at the Beijing Electron-Positron ColliderⅡ(BEPC Ⅱ) accelerator transport line in IHEP. The development of the system is explained in this paper, along with descriptions of its photon detector and laser system. Results of GEANT4 simulation about the process of interaction between laser photons and electron, Cerenkov radiation in different medium are presented. The parameters of the laser pulse such as width, size and power are measured. Laser optical system and mechanical scanning system are designed and tested. The Cherenkov detector is set up for detecting the Compton photons. Mathematical processing methods of laser scanner are given. Measurement results show the laser transport and focus subsystem work in accordance with the design, and the stability of laser focus parameters can meet the requirement of beam profile measurement.
2015,
27: 065104.
doi: 10.11884/HPLPB201527.065104
Abstract:
In order to precisely measure the phase difference between two sweeping signals with rapid cycling mode, it is necessary to select a method of signal acquisition and phase difference measurement algorithms for the RF accelerated voltage of the CSNS/RCS (China Spallation Neutron Source/Rapid Cycling Synchrotron) RF system and beam signal. The frequencies of both signals change synchronously. In this paper, measurement algorithms of signals with the same frequency are introduced and the features and applicability of those algorithms are discussed. Secondly, two different FFT spectrum analysis algorithms are elaborated and compared, including FFT cross-spectral method and FFT interpolation method adding cosine window. Then a sweep signal phase difference measurement system is set up using NI virtual instrument technology and Labview graphical programming technology for simulating those algorithms. According to the simulation results, the method of FFT interpolation method adding cosine window can meet the requirements of the fast cycling sweep signal phase difference measurement precision.
In order to precisely measure the phase difference between two sweeping signals with rapid cycling mode, it is necessary to select a method of signal acquisition and phase difference measurement algorithms for the RF accelerated voltage of the CSNS/RCS (China Spallation Neutron Source/Rapid Cycling Synchrotron) RF system and beam signal. The frequencies of both signals change synchronously. In this paper, measurement algorithms of signals with the same frequency are introduced and the features and applicability of those algorithms are discussed. Secondly, two different FFT spectrum analysis algorithms are elaborated and compared, including FFT cross-spectral method and FFT interpolation method adding cosine window. Then a sweep signal phase difference measurement system is set up using NI virtual instrument technology and Labview graphical programming technology for simulating those algorithms. According to the simulation results, the method of FFT interpolation method adding cosine window can meet the requirements of the fast cycling sweep signal phase difference measurement precision.
2015,
27: 065105.
doi: 10.11884/HPLPB201527.065105
Abstract:
A series of S-band dummy loads are developed by microwave Group these years. After the simulation and optimization for the S-band series of dummy loads in CST, the simulation results show that all the dummy loads achieved a voltage standing wave ratio less than 1.04 as well as a frequency bandwidth more than 100 MHz (to satisfy voltage standing wave ratio less than 1.1). All the fabricated products of the mentioned dummy loads achieved a voltage standing wave ratio less than 1.05 in low power microwave test. Among which the 14-rod high power dummy load was tested for high power performance in South Korea, where VSWR of 1.093 was tested with a pulse repetition frequency of 60 Hz as well as a pulse width of 1 s and a klystron output power of 50.7 MW. The working state of the dummy load was stable. The other dummy loads mentioned were all assembled on accelerators domestic or abroad, all of which were very stable and reliable after a long time operation.
A series of S-band dummy loads are developed by microwave Group these years. After the simulation and optimization for the S-band series of dummy loads in CST, the simulation results show that all the dummy loads achieved a voltage standing wave ratio less than 1.04 as well as a frequency bandwidth more than 100 MHz (to satisfy voltage standing wave ratio less than 1.1). All the fabricated products of the mentioned dummy loads achieved a voltage standing wave ratio less than 1.05 in low power microwave test. Among which the 14-rod high power dummy load was tested for high power performance in South Korea, where VSWR of 1.093 was tested with a pulse repetition frequency of 60 Hz as well as a pulse width of 1 s and a klystron output power of 50.7 MW. The working state of the dummy load was stable. The other dummy loads mentioned were all assembled on accelerators domestic or abroad, all of which were very stable and reliable after a long time operation.
2015,
27: 066001.
doi: 10.11884/HPLPB201527.066001
Abstract:
Astronomical observation and theoretical motivations have strongly indicated that most of matter in the Universe is made of cold dark matter. A well-motivated class of dark matter candidate is Weakly Interacting Massive Particles (WIMPs). Neutron and WIMPs can produce nuclear recoils via elastic scattering off ordinary matter in terrestrial detectors to the point where neutron can bring a false positive reading. Of crucial importance to the direct detections of dark matter searches is to identify the neutron background and its influence. In order to measure the flux and spectrum of neutron background in China JinPing Underground Laboratory (CJPL), an efficient Gd-doped liquid scintillator detector which possesses a strong (n-) discrimination was developed. This paper reports the design and performance of the detector geometry, the type of liquid scintillators and photomultiplier tubes (PMT) as well as the low radioactivity surrounding materials and the energy calibration and the capability of neutron and gamma discrimination. Am-Be neutron source was used to evaluate the neutron detection efficiency and the result is (6.300.30)% above 0.2 MeV equivalent electron energy.
Astronomical observation and theoretical motivations have strongly indicated that most of matter in the Universe is made of cold dark matter. A well-motivated class of dark matter candidate is Weakly Interacting Massive Particles (WIMPs). Neutron and WIMPs can produce nuclear recoils via elastic scattering off ordinary matter in terrestrial detectors to the point where neutron can bring a false positive reading. Of crucial importance to the direct detections of dark matter searches is to identify the neutron background and its influence. In order to measure the flux and spectrum of neutron background in China JinPing Underground Laboratory (CJPL), an efficient Gd-doped liquid scintillator detector which possesses a strong (n-) discrimination was developed. This paper reports the design and performance of the detector geometry, the type of liquid scintillators and photomultiplier tubes (PMT) as well as the low radioactivity surrounding materials and the energy calibration and the capability of neutron and gamma discrimination. Am-Be neutron source was used to evaluate the neutron detection efficiency and the result is (6.300.30)% above 0.2 MeV equivalent electron energy.
2015,
27: 066002.
doi: 10.11884/HPLPB201527.066002
Abstract:
In order to realize high speed motion control with high precision, the load characteristics of the chopper disk were analyzed, and the mathematic model of the controlled object, which was a two-mass model composed of disk entity and drive motor, was established. Based on this model, a current-speed-position cascade controller was designed, and the select method of the adjusters structure and parameters was given, based on the engineering design method and modern control theory. With a rotation frequency of 27.5 Hz, the position perturbation error ranged from -1.325 25 s to 1.325 25 s, and the steady-state error was -2.583 s, which met neutron choppers application requirements.
In order to realize high speed motion control with high precision, the load characteristics of the chopper disk were analyzed, and the mathematic model of the controlled object, which was a two-mass model composed of disk entity and drive motor, was established. Based on this model, a current-speed-position cascade controller was designed, and the select method of the adjusters structure and parameters was given, based on the engineering design method and modern control theory. With a rotation frequency of 27.5 Hz, the position perturbation error ranged from -1.325 25 s to 1.325 25 s, and the steady-state error was -2.583 s, which met neutron choppers application requirements.
2015,
27: 065002.
doi: 10.11884/HPLPB201527.065002
Abstract:
A relaxation magnetohydrodynamics (MHD) model is proposed for the computation of an electromagnetically driven vacuum-plasma system. It is similar to seylers proposal in adopting full electromagnetic model, but is different in adopting the relaxed generalized Ohms law (electron inertia term omitted) as a constitutive relation to close the Maxwells equations. Therefore it is the most simplified model for the concerned correlative problems (Hall term could also be included without increasing independent variables). The dispersion relation is given to show its transition from electromagnetic propagation in vacuum to resistive MHD in plasma in a natural way. The phase and group velocities are finite for this system. A better time stepping is adopted to give a 3rd full order convergence in time domain without the stiff relaxation term restriction. Therefore it is convenient for explicit parallel computations.
A relaxation magnetohydrodynamics (MHD) model is proposed for the computation of an electromagnetically driven vacuum-plasma system. It is similar to seylers proposal in adopting full electromagnetic model, but is different in adopting the relaxed generalized Ohms law (electron inertia term omitted) as a constitutive relation to close the Maxwells equations. Therefore it is the most simplified model for the concerned correlative problems (Hall term could also be included without increasing independent variables). The dispersion relation is given to show its transition from electromagnetic propagation in vacuum to resistive MHD in plasma in a natural way. The phase and group velocities are finite for this system. A better time stepping is adopted to give a 3rd full order convergence in time domain without the stiff relaxation term restriction. Therefore it is convenient for explicit parallel computations.
