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RSS2018 Vol. 30, No. 11
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2018,
30: 110101.
doi: 10.11884/HPLPB201830.180248
Abstract:
A novel six-port-cylindrical hohlraum has been independently designed for laser-driven inertial confinement fusion in China.Initial full-beam implosion experiment of this hohlraum was carried out on the laser facility.Integral experimental data with the convergence ratio from 10 to 20 were successfully obtained, and the best YOC2D of the implosion was demonstrated up to 80.4%.
A novel six-port-cylindrical hohlraum has been independently designed for laser-driven inertial confinement fusion in China.Initial full-beam implosion experiment of this hohlraum was carried out on the laser facility.Integral experimental data with the convergence ratio from 10 to 20 were successfully obtained, and the best YOC2D of the implosion was demonstrated up to 80.4%.
2018,
30: 110102.
doi: 10.11884/HPLPB201830.180250
Abstract:
A high power 30/600 μm ytterbium doped double-cladding fiber with excellent power stability was fabricated by MCVD in-situ vapor phase/solution doping technology. The dopants of the silica fiber core include Yb2O3, Al2O3 and P2O5. The master oscillator power amplifier configuration based on back pump was constructed to test the Yb-doped fiber performance. In the experiment, the power of the seed was 189 W, the total power of the pump power was 4767 W, and the maximum output power was 4120 W with a slope efficiency of 85%. In addition, no stimulated Raman scattering was found in the output laser spectrum, and the 3dB band width was measured to be 1.6 nm. The fiber laser continued to work for one hour, the output power was stable at 4.1 kW.
A high power 30/600 μm ytterbium doped double-cladding fiber with excellent power stability was fabricated by MCVD in-situ vapor phase/solution doping technology. The dopants of the silica fiber core include Yb2O3, Al2O3 and P2O5. The master oscillator power amplifier configuration based on back pump was constructed to test the Yb-doped fiber performance. In the experiment, the power of the seed was 189 W, the total power of the pump power was 4767 W, and the maximum output power was 4120 W with a slope efficiency of 85%. In addition, no stimulated Raman scattering was found in the output laser spectrum, and the 3dB band width was measured to be 1.6 nm. The fiber laser continued to work for one hour, the output power was stable at 4.1 kW.
2018,
30: 111001.
doi: 10.11884/HPLPB201830.180177
Abstract:
In view of the cooling problem of high power lasers, the existing traditional working fluids are replaced by the latent functionally thermal fluid. The laminar flow and heat transfer characteristics of the latent heat functionally thermal fluid and that of deionized water in a piece of pin-fin micro channels with height of 4 mm, width 2 mm and spacing 1 mm were experimentally studied. The results show that when Reynolds Number ranges 625-1125, the latent functionally thermal fluid shows better cooling performance and lower wall temperature than the deionized water, and it has an optimum concentration value; Its average Nusselt number is greater than that of the deionized water, and the average Nusselt number increases with the Reynolds number. To clearly demonstrate the relationship between the average Nusselt number, Reynolds number, mass concentration and Prandtl number, an experimental formula was further fitted based on the experimental data, the maximum relative deviation is 16.9%, which is acceptable for experiments. Along the length in the direction of flow, there exists an optimal length for a stable local heat transfer enhancement section.
In view of the cooling problem of high power lasers, the existing traditional working fluids are replaced by the latent functionally thermal fluid. The laminar flow and heat transfer characteristics of the latent heat functionally thermal fluid and that of deionized water in a piece of pin-fin micro channels with height of 4 mm, width 2 mm and spacing 1 mm were experimentally studied. The results show that when Reynolds Number ranges 625-1125, the latent functionally thermal fluid shows better cooling performance and lower wall temperature than the deionized water, and it has an optimum concentration value; Its average Nusselt number is greater than that of the deionized water, and the average Nusselt number increases with the Reynolds number. To clearly demonstrate the relationship between the average Nusselt number, Reynolds number, mass concentration and Prandtl number, an experimental formula was further fitted based on the experimental data, the maximum relative deviation is 16.9%, which is acceptable for experiments. Along the length in the direction of flow, there exists an optimal length for a stable local heat transfer enhancement section.
2018,
30: 111002.
doi: 10.11884/HPLPB201830.180063
Abstract:
To get the best results in the simulation of designing a hollow-duct pump-coupling system, we measured the actual directivity of bars of laser diode arrays. Compared to the model with an ideal directivity of bars, the decrease in the coupling efficiency is as large as 11.2% in our model with the actual directivity of bars. A larger transmission loss and a worse intensity distribution of the pump field are got at the same time. The results of the simulation are well matched with that of the experiment. It is concluded that simulating with the actual directivity of bars is essential and more accurate.
To get the best results in the simulation of designing a hollow-duct pump-coupling system, we measured the actual directivity of bars of laser diode arrays. Compared to the model with an ideal directivity of bars, the decrease in the coupling efficiency is as large as 11.2% in our model with the actual directivity of bars. A larger transmission loss and a worse intensity distribution of the pump field are got at the same time. The results of the simulation are well matched with that of the experiment. It is concluded that simulating with the actual directivity of bars is essential and more accurate.
2018,
30: 111003.
doi: 10.11884/HPLPB201830.180262
Abstract:
Electron optical injection is an efficient all-optical injection scheme in laser wakefield accelerations. However, low-charge and large emittance electron beam is still not suitable for many practical applications. This paper presents a novel injection scheme by colliding a tightly focused super-Gaussian laser with a Gaussian pump laser. It is found that the emittance of electron beam becomes almost an order of magnitude lower than that of all-Gaussian case, while the charge of electron bunch is conserved. It is also found that the electron emittance is mainly attributed to off-axis injected electrons by a Hamiltonian model. This unique ability will pave the way towards the generation of high-quality electron beams and extend the applications of laser-plasma accelerators.
Electron optical injection is an efficient all-optical injection scheme in laser wakefield accelerations. However, low-charge and large emittance electron beam is still not suitable for many practical applications. This paper presents a novel injection scheme by colliding a tightly focused super-Gaussian laser with a Gaussian pump laser. It is found that the emittance of electron beam becomes almost an order of magnitude lower than that of all-Gaussian case, while the charge of electron bunch is conserved. It is also found that the electron emittance is mainly attributed to off-axis injected electrons by a Hamiltonian model. This unique ability will pave the way towards the generation of high-quality electron beams and extend the applications of laser-plasma accelerators.
2018,
30: 111004.
doi: 10.11884/HPLPB201830.180013
Abstract:
The gain generator assembly is the core component which influences the recovered pressure of high energy deuterium fluoride(DF) chemical laser. The recovered pressure of DF laser exhaust gas using traditional gain generator assembly is about 6.7 kPa. A compact type of TRIP gain generator assembly was designed, with breakthroughs on the key techniques of running with high cavity pressure, primary stream curtain and restraining regurgitant stream of the laser cavity boundary wall. The recovered pressure of the DF laser was increased obviously. The test results show that the recovered pressure of the laser exhaust gas and the power flux were both increased effectively with the increase of the mass flow rate in the range of 1.3~3.3 g·s-1·cm-2. When the mass flow rate was 3.3 g·s-1·cm-2, the DF laser could operate efficiently at 26.7 kPa background pressure (air pressure of 10 km altitude).
The gain generator assembly is the core component which influences the recovered pressure of high energy deuterium fluoride(DF) chemical laser. The recovered pressure of DF laser exhaust gas using traditional gain generator assembly is about 6.7 kPa. A compact type of TRIP gain generator assembly was designed, with breakthroughs on the key techniques of running with high cavity pressure, primary stream curtain and restraining regurgitant stream of the laser cavity boundary wall. The recovered pressure of the DF laser was increased obviously. The test results show that the recovered pressure of the laser exhaust gas and the power flux were both increased effectively with the increase of the mass flow rate in the range of 1.3~3.3 g·s-1·cm-2. When the mass flow rate was 3.3 g·s-1·cm-2, the DF laser could operate efficiently at 26.7 kPa background pressure (air pressure of 10 km altitude).
2018,
30: 112001.
doi: 10.11884/HPLPB201830.180184
Abstract:
Poly-α-methylstyrene (PAMS) is one of the most important mandrel materials used in the fabrication of laser inertial confinement fusion (ICF) targets. The effects of the molecular weight on the degradation products and degradation temperature of PAMS were investigated using fast pyrolysis gas chromatography-mass spectrometry (Py-GC-MS), thermogravimetric analysis (TG/DTG) and isothermal degradation activation energy of PAMS was calculated by Arrhenius equations. The Py-GC-MS results show that the pyrolysis of PAMS was found to yield α-methylstyrene monomer exclusively.Moreover, it also suggested that the effect of molecular weight on the degradation products of PAMS can be neglected. The TG results indicate that the thermal degradation temperature decreases as the molecular weight of PAMS increases, and the main thermal degradation temperature ranges from 240 to 450 ℃.Finally, with the decrease of molecular weight and the increase of thermal degradation rate, the activation energy of thermal degradation of PAMS increases.
Poly-α-methylstyrene (PAMS) is one of the most important mandrel materials used in the fabrication of laser inertial confinement fusion (ICF) targets. The effects of the molecular weight on the degradation products and degradation temperature of PAMS were investigated using fast pyrolysis gas chromatography-mass spectrometry (Py-GC-MS), thermogravimetric analysis (TG/DTG) and isothermal degradation activation energy of PAMS was calculated by Arrhenius equations. The Py-GC-MS results show that the pyrolysis of PAMS was found to yield α-methylstyrene monomer exclusively.Moreover, it also suggested that the effect of molecular weight on the degradation products of PAMS can be neglected. The TG results indicate that the thermal degradation temperature decreases as the molecular weight of PAMS increases, and the main thermal degradation temperature ranges from 240 to 450 ℃.Finally, with the decrease of molecular weight and the increase of thermal degradation rate, the activation energy of thermal degradation of PAMS increases.
2018,
30: 112002.
doi: 10.11884/HPLPB201830.180207
Abstract:
To design the monochorator beamlines of synchrotron radiation, develop X-FELs and make X-ray diagnoses of inertia confinement fusion as well as simulate dynamic process in extreme physical conditions, a useful tool and a platform, X-LAB, for optical design, optimization and simulation with the independent intellectual property rights was developed. With friendly interface, X-LAB has the functions of sequence ray-tracing, vector diffraction simulation and layout drawing of complex micro-structure optical elements. Also, it is easy to operate and can provide accustomed service, characteristic functions for users to freely design, optimize an optical system. Currently, X-LAB has been applied in designs and simulations of the 3B1 monochromatic beamline in Beijing Synchrotron Radiation Facility with spectral resolution 1000 and spectral range 10~100 eV, the X-ray diagnosis optical systems of inertia confinement fusion and dynamic process in extreme physical conditions, the KB microscope with spatial resolution up to 6 μm, and the layout drawing of photon sieves.
To design the monochorator beamlines of synchrotron radiation, develop X-FELs and make X-ray diagnoses of inertia confinement fusion as well as simulate dynamic process in extreme physical conditions, a useful tool and a platform, X-LAB, for optical design, optimization and simulation with the independent intellectual property rights was developed. With friendly interface, X-LAB has the functions of sequence ray-tracing, vector diffraction simulation and layout drawing of complex micro-structure optical elements. Also, it is easy to operate and can provide accustomed service, characteristic functions for users to freely design, optimize an optical system. Currently, X-LAB has been applied in designs and simulations of the 3B1 monochromatic beamline in Beijing Synchrotron Radiation Facility with spectral resolution 1000 and spectral range 10~100 eV, the X-ray diagnosis optical systems of inertia confinement fusion and dynamic process in extreme physical conditions, the KB microscope with spatial resolution up to 6 μm, and the layout drawing of photon sieves.
2018,
30: 113001.
doi: 10.11884/HPLPB201830.180086
Abstract:
For calculating microwave breakdown electric field in air simply and instantly, we give a new formula adopting characteristic diffusion length, which is combined with basic parameters in gas discharge and based on electron diffusion model. We fit the relationship between equivalent direct-current electric field and characteristic diffusion length from experiment recorded by A D Macdonald (1966), thus to avoid the influence of uncertainty of gas parameters on calculation accuracy. According to the definition of equivalent direct-current electric field, we give another formula to calculate breakdown electric field, which applies to a high air pressure. Also, in consideration of electric diffusion model and vacuum multipactor discharge based on secondary electron emission, we further give a formula applicable to a wide air pressure range by using a rational equivalent diffusion length. Compared with the formula by Yu Ming (2007), our results are more consistent with Macdonald's experimental value.
For calculating microwave breakdown electric field in air simply and instantly, we give a new formula adopting characteristic diffusion length, which is combined with basic parameters in gas discharge and based on electron diffusion model. We fit the relationship between equivalent direct-current electric field and characteristic diffusion length from experiment recorded by A D Macdonald (1966), thus to avoid the influence of uncertainty of gas parameters on calculation accuracy. According to the definition of equivalent direct-current electric field, we give another formula to calculate breakdown electric field, which applies to a high air pressure. Also, in consideration of electric diffusion model and vacuum multipactor discharge based on secondary electron emission, we further give a formula applicable to a wide air pressure range by using a rational equivalent diffusion length. Compared with the formula by Yu Ming (2007), our results are more consistent with Macdonald's experimental value.
2018,
30: 113002.
doi: 10.11884/HPLPB201830.180172
Abstract:
This paper presents the design of a novel dual-mode dual-band bandpass filter with good selectivity. The resonant structure of the filter consists of two short-circuited stub loaded resonators (SSLRs) connected to the same grounded metal column. Firstly, the resonant frequency of a single SSLR is analyzed by odd-/even-mode analysis method and the variation regulation of single SSLR resonant frequency is obtained. Secondly, in order to realize the miniaturization of the filter, two SSLRs are connected to the same metal column and then the microstrip line is folded, and the change in the passband of the filter is analyzed by adjusting the length of the branch. Thirdly, in the design, double-stub feeders are used to feed the two resonators separately and the source-load coupling is introduced, so that an additional transmission zero can be provided in the upper stopband to increase the stop-band suppression. Finally the transmission zeros of the filter are analyzed and the rules of variation are summarized to improve the selection characteristics of the filter. Based on this analysis, the filter is simulated, processed and tested, and the final physical measurement results are consistent with the software simulation results.
This paper presents the design of a novel dual-mode dual-band bandpass filter with good selectivity. The resonant structure of the filter consists of two short-circuited stub loaded resonators (SSLRs) connected to the same grounded metal column. Firstly, the resonant frequency of a single SSLR is analyzed by odd-/even-mode analysis method and the variation regulation of single SSLR resonant frequency is obtained. Secondly, in order to realize the miniaturization of the filter, two SSLRs are connected to the same metal column and then the microstrip line is folded, and the change in the passband of the filter is analyzed by adjusting the length of the branch. Thirdly, in the design, double-stub feeders are used to feed the two resonators separately and the source-load coupling is introduced, so that an additional transmission zero can be provided in the upper stopband to increase the stop-band suppression. Finally the transmission zeros of the filter are analyzed and the rules of variation are summarized to improve the selection characteristics of the filter. Based on this analysis, the filter is simulated, processed and tested, and the final physical measurement results are consistent with the software simulation results.
2018,
30: 113003.
doi: 10.11884/HPLPB201830.180246
Abstract:
The tilt of inner conductor unavoidably occurs in coaxial gyrotrons. The effects of tilted inner conductor on eigenvalue, quality factor Q, resonant frequency, transverse electric field, mode competition and electronic efficiency are presented. The theory is illustrated in a 170 GHz TE31, 12 corrugated coaxial-gyrotron. The results indicate that eigenvalue and quality factor Q increase slightly when the tilt angle θ of inner conductor increases. However, within the range of 0-0.5°, the electronic efficiency decreases slightly when θ grows. If θ increases to 1.3°, the efficiency of beam-wave interaction reduces to 5% because mode competition becomes serious and the transverse electric field is distorted severely. Effected by the tilted inner conductor, the resonant frequency of cavity increases slightly with θ rising.
The tilt of inner conductor unavoidably occurs in coaxial gyrotrons. The effects of tilted inner conductor on eigenvalue, quality factor Q, resonant frequency, transverse electric field, mode competition and electronic efficiency are presented. The theory is illustrated in a 170 GHz TE31, 12 corrugated coaxial-gyrotron. The results indicate that eigenvalue and quality factor Q increase slightly when the tilt angle θ of inner conductor increases. However, within the range of 0-0.5°, the electronic efficiency decreases slightly when θ grows. If θ increases to 1.3°, the efficiency of beam-wave interaction reduces to 5% because mode competition becomes serious and the transverse electric field is distorted severely. Effected by the tilted inner conductor, the resonant frequency of cavity increases slightly with θ rising.
2018,
30: 113101.
doi: 10.11884/HPLPB201830.180247
Abstract:
Electron trajectory center deviation and magnetic field errors of undulator have a great influence on the performances of CTFEL facility, which were limited in the range of specification requirements by preliminary design and post measurement and optimization. In the preliminary design, the global system errors were avoided as far as possible: the magnetic structure has a planar anti-symmetric structure to ensure the coincidence of electron trajectory center and undulator magnetic axis; the special design of magnetic structure end weakens the influence of gap on second integral of magnetic field at undulator exit; the beam and frame of the mechanical system have good rigidity and the control system with close-loop configure guarantees high accuracy of the gap control, all of which limit the magnetic field errors caused by the gap inconsistency. The residual global system errors and local random errors of the magnetic field were reduced in the later measurement and optimization: the longitudinal and transverse distributions of magnetic field were measured using magnetic field measurement bench and then the undulator field was shimmed and optimized by adjusting the positions of standard unit components. Finally, the electron trajectory center deviation, peak-to-peak error, phase error and good field range error meet the requirements of specification after optimization.
Electron trajectory center deviation and magnetic field errors of undulator have a great influence on the performances of CTFEL facility, which were limited in the range of specification requirements by preliminary design and post measurement and optimization. In the preliminary design, the global system errors were avoided as far as possible: the magnetic structure has a planar anti-symmetric structure to ensure the coincidence of electron trajectory center and undulator magnetic axis; the special design of magnetic structure end weakens the influence of gap on second integral of magnetic field at undulator exit; the beam and frame of the mechanical system have good rigidity and the control system with close-loop configure guarantees high accuracy of the gap control, all of which limit the magnetic field errors caused by the gap inconsistency. The residual global system errors and local random errors of the magnetic field were reduced in the later measurement and optimization: the longitudinal and transverse distributions of magnetic field were measured using magnetic field measurement bench and then the undulator field was shimmed and optimized by adjusting the positions of standard unit components. Finally, the electron trajectory center deviation, peak-to-peak error, phase error and good field range error meet the requirements of specification after optimization.
2018,
30: 113201.
doi: 10.11884/HPLPB201830.180082
Abstract:
The increased development of information industry and relevant radio communication services is making the spectrum management problem more challenging to solve. A suitable spectrum management method enables transmitters to reuse the frequency efficiently and the user equipment (UE) can select the optimum base station. The radio environment map (REM) concept has been proposed as a tool to solve spectrum scarcity and improve spectrum utilization, making different users share spectrum resource efficiently. The REMs are becoming an increasingly popular method for interference management and resource assignment. The reason for this is that REMs can be constructed without the need for surveys or complex calibration processes which are costly and time consuming. This paper gives Shepard interpolation techniques and modifies it in some respects for estimating radio environments with a limited number of measurement data, thus constructing accurate REMs. Additionally, it presents our systematic investigation of the impact of the number and distribution of measurements using the averaged root mean square error (RMSE) as the performance metric. Simulation results show that increasing the number of measurements with the clustering sampling and the modified Shepard interpolation technique, the most accurate REM is obtained in terms of the performance metric RMSE. And the interpolation accuracy can be improved by almost 14 dB with the modified method, which proves that our approach can effectively determine sharing conditions of radio spectrum use both in time and space.
The increased development of information industry and relevant radio communication services is making the spectrum management problem more challenging to solve. A suitable spectrum management method enables transmitters to reuse the frequency efficiently and the user equipment (UE) can select the optimum base station. The radio environment map (REM) concept has been proposed as a tool to solve spectrum scarcity and improve spectrum utilization, making different users share spectrum resource efficiently. The REMs are becoming an increasingly popular method for interference management and resource assignment. The reason for this is that REMs can be constructed without the need for surveys or complex calibration processes which are costly and time consuming. This paper gives Shepard interpolation techniques and modifies it in some respects for estimating radio environments with a limited number of measurement data, thus constructing accurate REMs. Additionally, it presents our systematic investigation of the impact of the number and distribution of measurements using the averaged root mean square error (RMSE) as the performance metric. Simulation results show that increasing the number of measurements with the clustering sampling and the modified Shepard interpolation technique, the most accurate REM is obtained in terms of the performance metric RMSE. And the interpolation accuracy can be improved by almost 14 dB with the modified method, which proves that our approach can effectively determine sharing conditions of radio spectrum use both in time and space.
2018,
30: 113202.
doi: 10.11884/HPLPB201830.180203
Abstract:
The influence of magnetized stratified plasma sheath on the propagation characteristics of oblique electromagnetic waves is analyzed by the hybrid matrix method. The variation of transmission coefficient of electromagnetic wave with frequency under magnetic field and the polarization characteristics of electromagnetic wave with different incident angles under magnetic field are calculated respectively. Taking the GPS navigation right hand circularly polarized wave as an example, the influence of magnetic field and electron density on the right-hand circular polarization(RCP) electromagnetic wave is studied. The results show that the magnetic field can move the stop-band of the right-handed circular polarization wave towards the high frequency direction in the plasma. In addition, the magnetic field can improve the polarization characteristic of the circular polarization wave at oblique incidence to some extent, which is beneficial to the reception of the GPS signal.
The influence of magnetized stratified plasma sheath on the propagation characteristics of oblique electromagnetic waves is analyzed by the hybrid matrix method. The variation of transmission coefficient of electromagnetic wave with frequency under magnetic field and the polarization characteristics of electromagnetic wave with different incident angles under magnetic field are calculated respectively. Taking the GPS navigation right hand circularly polarized wave as an example, the influence of magnetic field and electron density on the right-hand circular polarization(RCP) electromagnetic wave is studied. The results show that the magnetic field can move the stop-band of the right-handed circular polarization wave towards the high frequency direction in the plasma. In addition, the magnetic field can improve the polarization characteristic of the circular polarization wave at oblique incidence to some extent, which is beneficial to the reception of the GPS signal.
2018,
30: 113203.
doi: 10.11884/HPLPB201830.180257
Abstract:
In order to apply the navigation solution output from the satellite navigation receiver to applications such as aircraft navigation and weapon launching testing, it is necessary to convert the geodetic height of the navigation solution to coarse normal height, but the demands for the coarse normal height in different application fields are different. To meet the normal height estimation requirements of different precisions, and to support the actual satellite navigation receiver application with low running time and storage space overhead, this paper proposes a coarse normal height estimation algorithm based on the simplified EGM96 model. Adopting the 360-degree 360-order EGM96 Earth gravity field model and the 2190-degree 2159-order EGM2008 Earth gravity field model, the running time and calculation accuracy of the coarse normal height estimation algorithm are evaluated. The test and comparative analysis of the grid points in the global region and the Asia-Pacific region show that the coarse normal height estimation algorithm can obtain the coarse normal height at different levels of accuracy, meeting the accuracy and timeliness requirements of the coarse normal height estimation with the satellite navigation receiver in the Asia-Pacific region and the global region.
In order to apply the navigation solution output from the satellite navigation receiver to applications such as aircraft navigation and weapon launching testing, it is necessary to convert the geodetic height of the navigation solution to coarse normal height, but the demands for the coarse normal height in different application fields are different. To meet the normal height estimation requirements of different precisions, and to support the actual satellite navigation receiver application with low running time and storage space overhead, this paper proposes a coarse normal height estimation algorithm based on the simplified EGM96 model. Adopting the 360-degree 360-order EGM96 Earth gravity field model and the 2190-degree 2159-order EGM2008 Earth gravity field model, the running time and calculation accuracy of the coarse normal height estimation algorithm are evaluated. The test and comparative analysis of the grid points in the global region and the Asia-Pacific region show that the coarse normal height estimation algorithm can obtain the coarse normal height at different levels of accuracy, meeting the accuracy and timeliness requirements of the coarse normal height estimation with the satellite navigation receiver in the Asia-Pacific region and the global region.
2018,
30: 114001.
doi: 10.11884/HPLPB201830.180208
Abstract:
The thermal deformation of grids assembly is the main factor affecting the working performance and working life of the ion thruster. In order to study the distribution and variation of the temperature field in the process of grids assembly heating, the method of accurately simulating the grid temperature field is explored. The full size finite element model of the 1/12 grids assembly is established for the heat transfer analysis. Meanwhile, the temperature measurement platform built in the laboratory, the transient temperature changes of the grids assembly in the atmosphere are measured. Comparison between the finite element analysis and test results shows that, the average error of the accelerated grid is 14.4%, the average error of the screen grid is 9.7%, the maximum error of two grids is less than 18.4%, and the credibility and rationality of the finite element model and the method is verified.
The thermal deformation of grids assembly is the main factor affecting the working performance and working life of the ion thruster. In order to study the distribution and variation of the temperature field in the process of grids assembly heating, the method of accurately simulating the grid temperature field is explored. The full size finite element model of the 1/12 grids assembly is established for the heat transfer analysis. Meanwhile, the temperature measurement platform built in the laboratory, the transient temperature changes of the grids assembly in the atmosphere are measured. Comparison between the finite element analysis and test results shows that, the average error of the accelerated grid is 14.4%, the average error of the screen grid is 9.7%, the maximum error of two grids is less than 18.4%, and the credibility and rationality of the finite element model and the method is verified.
2018,
30: 114002.
doi: 10.11884/HPLPB201830.180131
Abstract:
Surface discharge effect of spacecraft insulating material in space irradiation environment is one of the main factors that threaten spacecraft safety. To investigate the pattern and influencing factors of the electrostatic discharge of polytetrafluoroethylene (PTFE) in complex ionization environment, the flashover voltage of PTFE under high voltage direct current (DC) in high vacuum and during low energy electron irradiation were experimentally obtained, the trap density before and after irradiation was tested by isothermal surface potential decay, and the influencing factors of flashover voltage were analyzed. The results show that the surface flashover voltage of PTFE under the irradiation with electron energy of 19~25keV is higher than that under no irradiation. Higher electron energy leads to smaller positive charge density on surface of PTFE and larger trap density, decreasing deformity of surface electric field, increasing the flashover voltage finally. On the condition that electron energy remains the same, the flashover voltage of PTFE would be lower with the increasing electron beam density, number of initial electrons and number of secondary electrons.
Surface discharge effect of spacecraft insulating material in space irradiation environment is one of the main factors that threaten spacecraft safety. To investigate the pattern and influencing factors of the electrostatic discharge of polytetrafluoroethylene (PTFE) in complex ionization environment, the flashover voltage of PTFE under high voltage direct current (DC) in high vacuum and during low energy electron irradiation were experimentally obtained, the trap density before and after irradiation was tested by isothermal surface potential decay, and the influencing factors of flashover voltage were analyzed. The results show that the surface flashover voltage of PTFE under the irradiation with electron energy of 19~25keV is higher than that under no irradiation. Higher electron energy leads to smaller positive charge density on surface of PTFE and larger trap density, decreasing deformity of surface electric field, increasing the flashover voltage finally. On the condition that electron energy remains the same, the flashover voltage of PTFE would be lower with the increasing electron beam density, number of initial electrons and number of secondary electrons.
2018,
30: 114003.
doi: 10.11884/HPLPB201830.180117
Abstract:
Tomography particle image velocimetry (Tomo-PIV) is a laser speed measurement technique that obtains a three-dimensional velocity field in a space. Based on the Tomo-PIV imaging theory, this paper analyzes the relation between optics model of trace particle imaging and the three-dimensional discrete projection method of CT image reconstruction. A new synthetic images computing method which corresponds to the real wind tunnel's parameters are proposed. Then, a simulation laser illumination system with an irradiated volume of 80 mm×100 mm×100 mm is developed. The simulated Tomo-PIV images are obtained from the three-dimensional trace particles imaging model programmed by MATLAB. The factors affecting the imaging quality of PIV system are analyzed. Comparison of the synthetic images with the real particle images in which the number of particles per pixel is 0.007 7 shows the correctness of this simulation method.
Tomography particle image velocimetry (Tomo-PIV) is a laser speed measurement technique that obtains a three-dimensional velocity field in a space. Based on the Tomo-PIV imaging theory, this paper analyzes the relation between optics model of trace particle imaging and the three-dimensional discrete projection method of CT image reconstruction. A new synthetic images computing method which corresponds to the real wind tunnel's parameters are proposed. Then, a simulation laser illumination system with an irradiated volume of 80 mm×100 mm×100 mm is developed. The simulated Tomo-PIV images are obtained from the three-dimensional trace particles imaging model programmed by MATLAB. The factors affecting the imaging quality of PIV system are analyzed. Comparison of the synthetic images with the real particle images in which the number of particles per pixel is 0.007 7 shows the correctness of this simulation method.
Applications of MCMC method based on Bayesian hierarchical model in flash radiography reconstruction
2018,
30: 114004.
doi: 10.11884/HPLPB201830.180123
Abstract:
The Markov chain Monte Carlo(MCMC) method combined with Bayesian theory can not only use prior information flexibly, but also give the uncertainty of solution. There is a bright application prospect in quantitative diagnosis of flash radiography. For the optical path length data of the flash radiographic images, a posterior probability model is built by Bayesian hierarchical model, and the Markov chain is dynamically constructed by Gibbs sampling. Then the statistical results of linear attenuation coefficients and their uncertainty are obtained and compared with the constrained conjugate gradient (CCG) method. The results of numerical experiments show that the reconstruction result of MCMC method is approximately the same as the true data for the ideal FTO optical path length image. In the case of blurring and noise, the reconstructed result is equivalent to that by the CCG method. Even when the blurred optical path length data is interfered by high noise, the result of MCMC is slightly better than that of CCG. More importantly, the uncertainty of the reconstruction can be provided by MCMC method. The related work in this paper verifies the feasibility of MCMC reconstruction of flash radiographic images and lays a good foundation for MCMC reconstruction with blurred and noised transmissivity images.
The Markov chain Monte Carlo(MCMC) method combined with Bayesian theory can not only use prior information flexibly, but also give the uncertainty of solution. There is a bright application prospect in quantitative diagnosis of flash radiography. For the optical path length data of the flash radiographic images, a posterior probability model is built by Bayesian hierarchical model, and the Markov chain is dynamically constructed by Gibbs sampling. Then the statistical results of linear attenuation coefficients and their uncertainty are obtained and compared with the constrained conjugate gradient (CCG) method. The results of numerical experiments show that the reconstruction result of MCMC method is approximately the same as the true data for the ideal FTO optical path length image. In the case of blurring and noise, the reconstructed result is equivalent to that by the CCG method. Even when the blurred optical path length data is interfered by high noise, the result of MCMC is slightly better than that of CCG. More importantly, the uncertainty of the reconstruction can be provided by MCMC method. The related work in this paper verifies the feasibility of MCMC reconstruction of flash radiographic images and lays a good foundation for MCMC reconstruction with blurred and noised transmissivity images.
2018,
30: 114005.
doi: 10.11884/HPLPB201830.180135
Abstract:
This paper uses the technique of particle-in-cell to build an accelerating section model with external circuit to simulate the electron effect of deuterium ion beam bombarding the target surface and analyze the influence of secondary electrons on acceleration voltage, quality of deuterium ion beam and energy beam bombarding the target dynamically. The results indicate that the acceleration voltage will decrease 45% when there is 0.06 A electron current, which then lead to the deterioration of deuterium ion beam's quality. The energy of beam bombarding the target decrease 43.5%, which will influence the neutron yield.
This paper uses the technique of particle-in-cell to build an accelerating section model with external circuit to simulate the electron effect of deuterium ion beam bombarding the target surface and analyze the influence of secondary electrons on acceleration voltage, quality of deuterium ion beam and energy beam bombarding the target dynamically. The results indicate that the acceleration voltage will decrease 45% when there is 0.06 A electron current, which then lead to the deterioration of deuterium ion beam's quality. The energy of beam bombarding the target decrease 43.5%, which will influence the neutron yield.
2018,
30: 114006.
doi: 10.11884/HPLPB201830.180193
Abstract:
China Spallation Neutron Source (CSNS) white neutron source beamline mainly consists of one neutron beam window, one neutron beam shutter, two neutron beam collimators and some vacuum ducts. To guarantee a safe, stable, and reliable operation for the CSNS white neutron source beamline, a CSNS white neutron source beamline control system was developed under the Experimental Physics and Industrial Control System (EPICS) software framework. The system mainly consists of three subsystems: the motion control system of the neutron beam window, the neutron beam shutter and the neutron beam collimators; the vacuum control system; the control room. The remote monitoring and control of the main equipments of the CSNS white neutron source beamline was realized. The test results show that the system has the characteristics of high stability, high reliability and friendly operator interface, which satisfactorily meets operational needs.
China Spallation Neutron Source (CSNS) white neutron source beamline mainly consists of one neutron beam window, one neutron beam shutter, two neutron beam collimators and some vacuum ducts. To guarantee a safe, stable, and reliable operation for the CSNS white neutron source beamline, a CSNS white neutron source beamline control system was developed under the Experimental Physics and Industrial Control System (EPICS) software framework. The system mainly consists of three subsystems: the motion control system of the neutron beam window, the neutron beam shutter and the neutron beam collimators; the vacuum control system; the control room. The remote monitoring and control of the main equipments of the CSNS white neutron source beamline was realized. The test results show that the system has the characteristics of high stability, high reliability and friendly operator interface, which satisfactorily meets operational needs.
2018,
30: 115001.
doi: 10.11884/HPLPB201830.180144
Abstract:
This article mainly introduces a design circuit and control method for a pulse power supply of diode pumped solid state laser(DPSSL). According to the operating characteristics of the semiconductor laser, a circuit structure in which a front-stage capacitor charging circuit and a post-pulse current generating circuit are combined is used. Because the LCC resonant circuit has the characteristics of soft switching and resistance to load short-circuit and open-circuit, it can also realize the function of constant-current charging of the energy storage capacitor. Therefore, it is suitable for the charging circuit of the energy storage capacitor in the pulse power supply; the latter-stage pulse current generating circuit selects a high-power MOSFET as a master control device, utilizes the drain current controllability of the saturation region of the MOSFET, and generates a pulse current through the gate voltage control. The control part adopts a combination of analog and digital control methods to make the pulse power supply control more flexible, and add a given integrator in the pulse current given step, which can effectively control the pulse current rising process, suppress the current overshoot, improve the control accuracy, and make the pulse drive power supply generate a pulse current similar to a rectangular wave. An experimental platform with a pulse power of 28 kW was set up. The experimental parameters were: pulse current amplitude of 80 A, pulse voltage of 350 V, pulse width of 100 μs, and repetition frequency of 100 Hz.
This article mainly introduces a design circuit and control method for a pulse power supply of diode pumped solid state laser(DPSSL). According to the operating characteristics of the semiconductor laser, a circuit structure in which a front-stage capacitor charging circuit and a post-pulse current generating circuit are combined is used. Because the LCC resonant circuit has the characteristics of soft switching and resistance to load short-circuit and open-circuit, it can also realize the function of constant-current charging of the energy storage capacitor. Therefore, it is suitable for the charging circuit of the energy storage capacitor in the pulse power supply; the latter-stage pulse current generating circuit selects a high-power MOSFET as a master control device, utilizes the drain current controllability of the saturation region of the MOSFET, and generates a pulse current through the gate voltage control. The control part adopts a combination of analog and digital control methods to make the pulse power supply control more flexible, and add a given integrator in the pulse current given step, which can effectively control the pulse current rising process, suppress the current overshoot, improve the control accuracy, and make the pulse drive power supply generate a pulse current similar to a rectangular wave. An experimental platform with a pulse power of 28 kW was set up. The experimental parameters were: pulse current amplitude of 80 A, pulse voltage of 350 V, pulse width of 100 μs, and repetition frequency of 100 Hz.
2018,
30: 115002.
doi: 10.11884/HPLPB201830.180230
Abstract:
A dense plasma focus (DPF) device with a Mather chamber was developed. The working principle and system composition of the DPF device are introduced, and the design of the DPF chamber is discussed in detail. The following technical parameters of the device were achieved: average neutron yield greater than 5.0×108 /pulse(D-D) with neutron pulse width(FWHM) (40±5) ns when the charging voltage of the primary capacitors is greater than 19 kV and the deuterium gas pressure is 550-600 Pa. The device can be used for calibration of detector sensitivity in neutron and gamma radiation diagnostics, as well as to carry out researches on fast neutron radiography, neutron activation analysis and single event effect.
A dense plasma focus (DPF) device with a Mather chamber was developed. The working principle and system composition of the DPF device are introduced, and the design of the DPF chamber is discussed in detail. The following technical parameters of the device were achieved: average neutron yield greater than 5.0×108 /pulse(D-D) with neutron pulse width(FWHM) (40±5) ns when the charging voltage of the primary capacitors is greater than 19 kV and the deuterium gas pressure is 550-600 Pa. The device can be used for calibration of detector sensitivity in neutron and gamma radiation diagnostics, as well as to carry out researches on fast neutron radiography, neutron activation analysis and single event effect.
2018,
30: 115003.
doi: 10.11884/HPLPB201830.180181
Abstract:
The rod-pinch diode is a cylindrical pinched beam diode that generates an intense pulsed small diameter bremsstrahlung source for flash radiography. If the pulse power source has the inductive voltage adder structure in vacuum vessels, the mechanical deformation caused by its long cantilever arm and air pressure could induce visible concentricity deviation to the anode and cathode structure. To evaluate that the concentricity of the cathode and anode geometrical centers does have some effect on the physical characteristics of the rod-pinch diode and the gap closure, a positive polarity rod-pinch diode was designed to work at 1 MV, and three different values of eccentricity were used in experiment: less than 1%, 15.06%, 22.92%. The experimental results show that the diode impedance decay rate is increased with a larger concentricity deviation. This implies that the electrode plasma expansion is fast. A larger concentricity deviation results in the impedance mismatch and decrease in energy coupling efficiency between the diode and pulse power source at the magnetically limited phase.
The rod-pinch diode is a cylindrical pinched beam diode that generates an intense pulsed small diameter bremsstrahlung source for flash radiography. If the pulse power source has the inductive voltage adder structure in vacuum vessels, the mechanical deformation caused by its long cantilever arm and air pressure could induce visible concentricity deviation to the anode and cathode structure. To evaluate that the concentricity of the cathode and anode geometrical centers does have some effect on the physical characteristics of the rod-pinch diode and the gap closure, a positive polarity rod-pinch diode was designed to work at 1 MV, and three different values of eccentricity were used in experiment: less than 1%, 15.06%, 22.92%. The experimental results show that the diode impedance decay rate is increased with a larger concentricity deviation. This implies that the electrode plasma expansion is fast. A larger concentricity deviation results in the impedance mismatch and decrease in energy coupling efficiency between the diode and pulse power source at the magnetically limited phase.
2018,
30: 115101.
doi: 10.11884/HPLPB201830.180171
Abstract:
There are eight RF power sources for linac accelerator of China Spallation Neutron Source phase-I project, and each RF power source was controlled by one digital low level RF unit separately. The local control of digital low level RF is a non-EPICS system, which could not directly communicate with EPICS clients. Remote control of the low level RF local control system by EPICS clients is realized by embedding a C# type EPICS server to the upper control application, thus the low level RF local control was ported into the EPICS framework. Since its online deployment for linac low level RF control, the remote control system has been stable and reliable in operation.
There are eight RF power sources for linac accelerator of China Spallation Neutron Source phase-I project, and each RF power source was controlled by one digital low level RF unit separately. The local control of digital low level RF is a non-EPICS system, which could not directly communicate with EPICS clients. Remote control of the low level RF local control system by EPICS clients is realized by embedding a C# type EPICS server to the upper control application, thus the low level RF local control was ported into the EPICS framework. Since its online deployment for linac low level RF control, the remote control system has been stable and reliable in operation.
2018,
30: 116001.
doi: 10.11884/HPLPB201830.180158
Abstract:
Extremely high density neutrons could be produced in inertial confinement fusion, therefore the neutron-neutron collision process can no longer be neglected, especially that it leads to production of super-high energy neutrons of important value for diagnosis technique. For numerical simulation of neutron-neutron collision, Monte Carlo methods generally suffer from low efficiency, while deterministic methods have limited accuracy. In this paper, several measures are taken to improve the accuracy of deterministic method: Firstly, the phase space discretization of neutron transport calculation adopts discontinuous finite element method, and the numbers of angle discretization and the scattering order are relatively large; Secondly, direct Monte Carlo tallying method is used to obtain highly accurate multi-group cross sections; thirdly, a neutron-neutron collision source iteration method that converges to real solution is introduced. At last, numerical verification shows that the enhanced deterministic method has favorable stability and accuracy, the non-linear problem arise from consideration of neutron-neutron collision process can be solved with reliable accuracy.
Extremely high density neutrons could be produced in inertial confinement fusion, therefore the neutron-neutron collision process can no longer be neglected, especially that it leads to production of super-high energy neutrons of important value for diagnosis technique. For numerical simulation of neutron-neutron collision, Monte Carlo methods generally suffer from low efficiency, while deterministic methods have limited accuracy. In this paper, several measures are taken to improve the accuracy of deterministic method: Firstly, the phase space discretization of neutron transport calculation adopts discontinuous finite element method, and the numbers of angle discretization and the scattering order are relatively large; Secondly, direct Monte Carlo tallying method is used to obtain highly accurate multi-group cross sections; thirdly, a neutron-neutron collision source iteration method that converges to real solution is introduced. At last, numerical verification shows that the enhanced deterministic method has favorable stability and accuracy, the non-linear problem arise from consideration of neutron-neutron collision process can be solved with reliable accuracy.
2018,
30: 116002.
doi: 10.11884/HPLPB201830.170525
Abstract:
Lithium oxide (Li2O) is one of the best tritium breeding materials. A new wet process, freeze drying method, was used to prepare Li2O pebbles by Li2CO3 powder. Preliminary fabrication tests including freezing, calcination and decomposition were carried out to investigate the fabrication technique parameter of Li2O pebbles. It is suggested that Li2O pebbles can be fabricated by the decomposition of Li2CO3 pebbles at 720 ℃, which were prepared by freeze drying method and calcinated at 650 ℃. Li2O pebbles sintered at 900 ℃ have a diameter of 0.8 mm, grain size of 9 μm, density of 69.5% theoretical density and porous structure.
Lithium oxide (Li2O) is one of the best tritium breeding materials. A new wet process, freeze drying method, was used to prepare Li2O pebbles by Li2CO3 powder. Preliminary fabrication tests including freezing, calcination and decomposition were carried out to investigate the fabrication technique parameter of Li2O pebbles. It is suggested that Li2O pebbles can be fabricated by the decomposition of Li2CO3 pebbles at 720 ℃, which were prepared by freeze drying method and calcinated at 650 ℃. Li2O pebbles sintered at 900 ℃ have a diameter of 0.8 mm, grain size of 9 μm, density of 69.5% theoretical density and porous structure.
2018,
30: 116003.
doi: 10.11884/HPLPB201830.180204
Abstract:
In order to study the associated particle imaging technique, it is necessary to develop the first-generation associated particle tube with the associated particle detector. Therefore, the key techniques, such as D-T generator, the relationship between neutrons and alpha particles in D-T reaction, associated particle detector and readout circuit, are studied. The performance of the position sensitive photomultiplier (PSPMT)and two readout circuits are tested in the experiment and design of the first-generation associated particle tube with the associated particle detector. It is proved that the SCDC readout circuit has smaller distortion and higher position resolution than the DPC readout circuit. The association between alpha particles and neutrons in time and position is measured, and the neutron angle uncertainty is about 7°, which is consistent with the theory ethical value.
In order to study the associated particle imaging technique, it is necessary to develop the first-generation associated particle tube with the associated particle detector. Therefore, the key techniques, such as D-T generator, the relationship between neutrons and alpha particles in D-T reaction, associated particle detector and readout circuit, are studied. The performance of the position sensitive photomultiplier (PSPMT)and two readout circuits are tested in the experiment and design of the first-generation associated particle tube with the associated particle detector. It is proved that the SCDC readout circuit has smaller distortion and higher position resolution than the DPC readout circuit. The association between alpha particles and neutrons in time and position is measured, and the neutron angle uncertainty is about 7°, which is consistent with the theory ethical value.
Power conversion efficiency of photovoltaic cells in semiconductor laser wireless power transmission
2018,
30: 119001.
doi: 10.11884/HPLPB201830.180097
Abstract:
In order to choose the best laser parameters and the photovoltaic cells (PV cells) parameters to reach a high power conversion efficiency (PCE) of the laser wireless power transmission (LWPT) system, we experimentally studied the output characteristics of the receiving system, the PV cells, under laser irradiation. The GaAs and Si PV cells were irradiated by laser with wavelengths of 808 nm and 915 nm, and the output characteristics and PCE of the PV cells under different conditions were analyzed. These conditions include: laser power intensity, laser incidence angle, temperature and material of the PV cells. In the experiment, when 808 nm laser power intensity increased from 0.06 W/cm2 to 0.37 W/cm2, the maximum output power of Si PV cell increased from 0.12 W to 0.32 W, but its PCE decreased from 50.9% to 21.2%; the maximum output power of GaAs PV cell increased from 0.40 W to 1.07 W, but its PCE decreased from 57.9% to 23.8%. The experimental results show that with the increase of laser power density, the output power of PV cells increases at first and then tends to be stable, but the temperature rise caused by high power intensity laser will lead to the decrease of power conversion efficiency of PV cells. So, the selection of laser power intensity and the temperature control of PV cells are keys to increase the PCE of LWPT system.
In order to choose the best laser parameters and the photovoltaic cells (PV cells) parameters to reach a high power conversion efficiency (PCE) of the laser wireless power transmission (LWPT) system, we experimentally studied the output characteristics of the receiving system, the PV cells, under laser irradiation. The GaAs and Si PV cells were irradiated by laser with wavelengths of 808 nm and 915 nm, and the output characteristics and PCE of the PV cells under different conditions were analyzed. These conditions include: laser power intensity, laser incidence angle, temperature and material of the PV cells. In the experiment, when 808 nm laser power intensity increased from 0.06 W/cm2 to 0.37 W/cm2, the maximum output power of Si PV cell increased from 0.12 W to 0.32 W, but its PCE decreased from 50.9% to 21.2%; the maximum output power of GaAs PV cell increased from 0.40 W to 1.07 W, but its PCE decreased from 57.9% to 23.8%. The experimental results show that with the increase of laser power density, the output power of PV cells increases at first and then tends to be stable, but the temperature rise caused by high power intensity laser will lead to the decrease of power conversion efficiency of PV cells. So, the selection of laser power intensity and the temperature control of PV cells are keys to increase the PCE of LWPT system.
2018,
30: 110000.
