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RSS2017 Vol. 29, No. 08
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2017,
29: 080201.
doi: 10.11884/HPLPB201729.170045
Abstract:
The micro-mechanical resonance accelerometer(MMRA) is used to measure the acceleration by detecting the change of resonant frequency of the sensitive element．This kind of sensor has become one of the important development direction of micro-sensors because it has many advantages such as frequency signal output，high stability, sensitivity and precision．This paper describes the key technologies, difficulties and corresponding solutions, development trends of MMRA. The key technologies include mechanical structure, excitation and detection methods, and methods of changing the resonator stiffness. The three mechanical structures of the resonator and the asymmetry caused by the error of the micro-lever process are analyzed; according to the piezoelectric properties of the resonators materials, MMRA can be divided into piezoelectric MMRA and non-piezoelectric MMRA, piezoelectric MMRA employs piezoelectric excitation/piezoelectric detection and non-piezoelectric are mainly electrostatic excitation/capacitance detection; there are two main methods to change the stiffness of the resonator: axial stress method and electrostatic stiffness method, whose principles and scopes are analyzed and compared. Development of MMRA mainly includes four technical difficulties: mechanical coupling, temperature characteristics, process error, assembly and packaging, and the corresponding solutions are given. Integration, static stiffness, new materials, multi-axis and higher performance will be the main development trends for MMRA in the future.
The micro-mechanical resonance accelerometer(MMRA) is used to measure the acceleration by detecting the change of resonant frequency of the sensitive element．This kind of sensor has become one of the important development direction of micro-sensors because it has many advantages such as frequency signal output，high stability, sensitivity and precision．This paper describes the key technologies, difficulties and corresponding solutions, development trends of MMRA. The key technologies include mechanical structure, excitation and detection methods, and methods of changing the resonator stiffness. The three mechanical structures of the resonator and the asymmetry caused by the error of the micro-lever process are analyzed; according to the piezoelectric properties of the resonators materials, MMRA can be divided into piezoelectric MMRA and non-piezoelectric MMRA, piezoelectric MMRA employs piezoelectric excitation/piezoelectric detection and non-piezoelectric are mainly electrostatic excitation/capacitance detection; there are two main methods to change the stiffness of the resonator: axial stress method and electrostatic stiffness method, whose principles and scopes are analyzed and compared. Development of MMRA mainly includes four technical difficulties: mechanical coupling, temperature characteristics, process error, assembly and packaging, and the corresponding solutions are given. Integration, static stiffness, new materials, multi-axis and higher performance will be the main development trends for MMRA in the future.
2017,
29: 081001.
doi: 10.11884/HPLPB201729.170067
Abstract:
In order to correct the defocus aberration in the thin-disk laser resonant cavity, a special water-cooled deformable mirror named as defocus-correction deformable mirror was designed and manufactured. The defocus-correction deformable mirror has 5 piezoelectric ceramic actuators, one located in the center of the round mirror surface and the other four arranged symmetrically on the mirrors circular periphery. The simulation of relationship between mirror thickness and surface deformation was carried out to gain the best defocus-correction result. Testing results show that, the deformable mirror, with optical surface quality better than 034 m PV, has extremely large stroke up to 16 m. In the wavefront correction experiments of thin-disk laser systems, the optical quality ( factor) of laser was improved from 19.5 to 6.5, which gives the vivid proof of the capability and effect of the defocus-correction deformable mirror.
In order to correct the defocus aberration in the thin-disk laser resonant cavity, a special water-cooled deformable mirror named as defocus-correction deformable mirror was designed and manufactured. The defocus-correction deformable mirror has 5 piezoelectric ceramic actuators, one located in the center of the round mirror surface and the other four arranged symmetrically on the mirrors circular periphery. The simulation of relationship between mirror thickness and surface deformation was carried out to gain the best defocus-correction result. Testing results show that, the deformable mirror, with optical surface quality better than 034 m PV, has extremely large stroke up to 16 m. In the wavefront correction experiments of thin-disk laser systems, the optical quality ( factor) of laser was improved from 19.5 to 6.5, which gives the vivid proof of the capability and effect of the defocus-correction deformable mirror.
2017,
29: 081002.
doi: 10.11884/HPLPB201729.170033
Abstract:
In the Nd: YAG thin disk laser system, there is a hydraulic entrance distance when the fluid flows through the gain medium. By using the Ansys simulation software, the influence of the different hydraulic entrance distances on the heat transfer coefficient of the fluid was discussed. The influence of the hydraulic entrance distance on the thermal stress and the beam transmission was analyzed. The cooling effect of different coolant is simulated. When the fluid was in different flow state, the relationship between the hydraulic entrance distance and the heat transfer coefficient of the fluid was studied, while the relationship between the hydraulic entrance distance and the temperature of the medium was also studied. The range of the optimal hydraulic entrance distance was obtained in the high power laser cooling system. The results show that when the fluid flows through the gain medium, the different hydraulic entrance distance only moves the heat transfer coefficient curve of the fluid regularly. Therefore, it can realize small temperature gradient in the medium, while reducing the thermal stress as well as the wavefront distortion by avoiding the distance region (0-2.25 mm) where the heat transfer coefficient curve changes greatly, and finally, achieve a better cooling effect.
In the Nd: YAG thin disk laser system, there is a hydraulic entrance distance when the fluid flows through the gain medium. By using the Ansys simulation software, the influence of the different hydraulic entrance distances on the heat transfer coefficient of the fluid was discussed. The influence of the hydraulic entrance distance on the thermal stress and the beam transmission was analyzed. The cooling effect of different coolant is simulated. When the fluid was in different flow state, the relationship between the hydraulic entrance distance and the heat transfer coefficient of the fluid was studied, while the relationship between the hydraulic entrance distance and the temperature of the medium was also studied. The range of the optimal hydraulic entrance distance was obtained in the high power laser cooling system. The results show that when the fluid flows through the gain medium, the different hydraulic entrance distance only moves the heat transfer coefficient curve of the fluid regularly. Therefore, it can realize small temperature gradient in the medium, while reducing the thermal stress as well as the wavefront distortion by avoiding the distance region (0-2.25 mm) where the heat transfer coefficient curve changes greatly, and finally, achieve a better cooling effect.
2017,
29: 081003.
doi: 10.11884/HPLPB201729.170091
Abstract:
Two-pulse bidirectional propagating amplification architecture, which has great application value in the field of inertial confinement fusion laser driver, is a new type of multi-pass amplification. To solve the problem of correcting two-pulse wavefront distortion with deformable mirrors in cavity position, this paper presents a coupling correcting method with double deformable mirrors and double Hartman-Shack sensors by the way of stitching two-pulse wavefront before compensating. Numerical simulations is carried out with the data of Shenguang-Ⅲ facility. As the result, the coupling correcting technology can effectively control both of two-pulse wavefront distortion and far-field energy distributions in spatial filter pinholes. The conclusion will provide theoretical guidance for designing and building adaptive optics system with two-pulse bidirectional propagating amplification architecture.
Two-pulse bidirectional propagating amplification architecture, which has great application value in the field of inertial confinement fusion laser driver, is a new type of multi-pass amplification. To solve the problem of correcting two-pulse wavefront distortion with deformable mirrors in cavity position, this paper presents a coupling correcting method with double deformable mirrors and double Hartman-Shack sensors by the way of stitching two-pulse wavefront before compensating. Numerical simulations is carried out with the data of Shenguang-Ⅲ facility. As the result, the coupling correcting technology can effectively control both of two-pulse wavefront distortion and far-field energy distributions in spatial filter pinholes. The conclusion will provide theoretical guidance for designing and building adaptive optics system with two-pulse bidirectional propagating amplification architecture.
2017,
29: 082001.
doi: 10.11884/HPLPB201729.170020
Abstract:
Reflector module is an important part of the laser facility, the rotation stability of which has a direct effect on the beams propagation. In order to obtain the rotations of reflectors due to ambient vibration, the finite element analysis is adopted. Finite model of a laser facility with mirror mount is built by the finite element analysis software based on full-structure and sub-structure methods. Then, the random vibration analysis is carried out, and the rotation angles of two reflectors are calculated. The result differences between these two methods are 3.99%,11.84%, which indicates that the analysis is reasonable based on sub-structure method when calculating the stability of large laser facility with mirror mount.
Reflector module is an important part of the laser facility, the rotation stability of which has a direct effect on the beams propagation. In order to obtain the rotations of reflectors due to ambient vibration, the finite element analysis is adopted. Finite model of a laser facility with mirror mount is built by the finite element analysis software based on full-structure and sub-structure methods. Then, the random vibration analysis is carried out, and the rotation angles of two reflectors are calculated. The result differences between these two methods are 3.99%,11.84%, which indicates that the analysis is reasonable based on sub-structure method when calculating the stability of large laser facility with mirror mount.
2017,
29: 082002.
doi: 10.11884/HPLPB201729.170564
Abstract:
Liquid hydrogen and deuterium have abundant electrical and optical properties at high pressure. A simple model to calculate the conductivity of low-Z materials was constructed. Combining the model with experiment, this paper introduces the study of the ionization and conductivity of liquid deuterium at around 70 GPa. The results show that, deuterium at this range of pressure has an ionization about 0.067%, conductivity about 2.87105（Wm)-1, which means the shocked deuterium reaches a conducting state with characteristic of metallic fluid. Apparently, the transition from the insulating molecular state to metallic state of deuterium begins at a lower pressure.
Liquid hydrogen and deuterium have abundant electrical and optical properties at high pressure. A simple model to calculate the conductivity of low-Z materials was constructed. Combining the model with experiment, this paper introduces the study of the ionization and conductivity of liquid deuterium at around 70 GPa. The results show that, deuterium at this range of pressure has an ionization about 0.067%, conductivity about 2.87105（Wm)-1, which means the shocked deuterium reaches a conducting state with characteristic of metallic fluid. Apparently, the transition from the insulating molecular state to metallic state of deuterium begins at a lower pressure.
2017,
29: 082003.
doi: 10.11884/HPLPB201729.170138
Abstract:
Laser-driven electrons can produce high-quality X-ray source with broad applications including measurement of shock-compressed matters, inertial confinement fusion and laboratory astrophysics. For high energy density experiments, bright high-resolution diagnosis radiation is required. To meet the requirement, it is decisive to optimize the production of hot electrons and radiation emission. In this paper, we combine the Particle-In-Cell and Monte Carlo simulation, firstly use near-critical-density plasma to accelerate high-charge energetic electrons (exceeds 600 nC, 15 MeV) by direct laser acceleration in self-focusing channel, then get enhanced energy conversion between electrons and photons, finally obtain brilliant micro-spot (FWHM200 m) high-energy X-rays via parameter optimization. Our findings provide a promising access to high-spatial-resolution (200 m) diagnostics, and it is hopeful to realize single-pulse transient imaging based on laser-plasma bremsstrahlung source.
Laser-driven electrons can produce high-quality X-ray source with broad applications including measurement of shock-compressed matters, inertial confinement fusion and laboratory astrophysics. For high energy density experiments, bright high-resolution diagnosis radiation is required. To meet the requirement, it is decisive to optimize the production of hot electrons and radiation emission. In this paper, we combine the Particle-In-Cell and Monte Carlo simulation, firstly use near-critical-density plasma to accelerate high-charge energetic electrons (exceeds 600 nC, 15 MeV) by direct laser acceleration in self-focusing channel, then get enhanced energy conversion between electrons and photons, finally obtain brilliant micro-spot (FWHM200 m) high-energy X-rays via parameter optimization. Our findings provide a promising access to high-spatial-resolution (200 m) diagnostics, and it is hopeful to realize single-pulse transient imaging based on laser-plasma bremsstrahlung source.
2017,
29: 083201.
doi: 10.11884/HPLPB201729.170093
Abstract:
Polytetrafluoroethylene(PTFE) is often used in spacecraft cable production for its excellent insulation and chemical stability. To study the surface flashover characteristics of PTFE, we conducted experiments under normal atmospheric pressure, with the DC voltage applied at the two ends of the PTFE samples, and the discharge voltage value, voltage and current waveform were obtained. The results show that with the increase of the number of flashovers, the discharge voltage increases at first and then stabilizes, and the average field strength is reduced. It is concluded that the change of the surface roughness and the chemical properties of the surface are important factors that influence the surface flashover voltage. According to the influence of the number of flashovers on the voltage, a method to describe the PTFE flashover voltage is proposed.
Polytetrafluoroethylene(PTFE) is often used in spacecraft cable production for its excellent insulation and chemical stability. To study the surface flashover characteristics of PTFE, we conducted experiments under normal atmospheric pressure, with the DC voltage applied at the two ends of the PTFE samples, and the discharge voltage value, voltage and current waveform were obtained. The results show that with the increase of the number of flashovers, the discharge voltage increases at first and then stabilizes, and the average field strength is reduced. It is concluded that the change of the surface roughness and the chemical properties of the surface are important factors that influence the surface flashover voltage. According to the influence of the number of flashovers on the voltage, a method to describe the PTFE flashover voltage is proposed.
2017,
29: 083202.
doi: 10.11884/HPLPB201729.160541
Abstract:
This paper investigates the thermal run away mechanism of metal oxide semiconductor field effect transistors (MOSFETs) in RS triggers. Simulations are performed to study the RS trigger damage threshold under different gate input and rising time, and the internal temperature distribution is plotted. Through the analysis, this paper concludes that the strong electromagnetic pulses with longer rise time should have higher peak intensity and longer time to damage RS triggers.
This paper investigates the thermal run away mechanism of metal oxide semiconductor field effect transistors (MOSFETs) in RS triggers. Simulations are performed to study the RS trigger damage threshold under different gate input and rising time, and the internal temperature distribution is plotted. Through the analysis, this paper concludes that the strong electromagnetic pulses with longer rise time should have higher peak intensity and longer time to damage RS triggers.
2017,
29: 083203.
doi: 10.11884/HPLPB201729.170022
Abstract:
The applicability of four different fast algorithms for shielding effectiveness (SE) prediction of rectangular metallic enclosures with apertures is evaluated, in order to choose appropriate algorithm for practical engineering problem. The SE values of 864 metallic enclosures with different shape, size and apertures are calculated using these four algorithms and compared to FDTD results. According to the variation of absolute error and curvilinear correlation coefficient in terms of dimension sizes of cavity and aperture, the applicable numbers of modes of these four different fast algorithms for shielding effectiveness (SE) prediction is determined eventually. The results show that Modal-MOM has the largest applicable number of modes, ILCM follows, and TLECM has the least applicable number of modes. These results provide a guidance for practical engineering applications.
The applicability of four different fast algorithms for shielding effectiveness (SE) prediction of rectangular metallic enclosures with apertures is evaluated, in order to choose appropriate algorithm for practical engineering problem. The SE values of 864 metallic enclosures with different shape, size and apertures are calculated using these four algorithms and compared to FDTD results. According to the variation of absolute error and curvilinear correlation coefficient in terms of dimension sizes of cavity and aperture, the applicable numbers of modes of these four different fast algorithms for shielding effectiveness (SE) prediction is determined eventually. The results show that Modal-MOM has the largest applicable number of modes, ILCM follows, and TLECM has the least applicable number of modes. These results provide a guidance for practical engineering applications.
2017,
29: 084101.
doi: 10.11884/HPLPB201729.170074
Abstract:
In order to compare the properties of nanoparticles synthesized from gaseous detonation and condensed explosives detonation, we carried out the investigation utilizing XRD, Raman and TEM methods. Condensed explosives detonation used cupric citrate xerogel as material, and detonated in the protection of nitrogen atmosphere; gaseous detonation used acetylacetone copper as material, detonated under the negative oxygen conditions with the explosion sources of H2 and O2, H2 and air. The results of XRD, Raman and TEM analyses show that the carbon encapsulated copper nanoparticles with good dispersibility can be obtained by both two detonation methods, and the degree of graphitization of carbon shell is high. Gaseous detonation can synthesize nanocrystals below 10 nm, and the size of nanocrystals by condensed explosives detonation is between 20-40 nm, and there are more empty shells. The gaseous detonation product has a carbon shell size between 2 and 3 nm, and the condensed explosive detonation product has a carbon shell size between 2 and 5 nm.
In order to compare the properties of nanoparticles synthesized from gaseous detonation and condensed explosives detonation, we carried out the investigation utilizing XRD, Raman and TEM methods. Condensed explosives detonation used cupric citrate xerogel as material, and detonated in the protection of nitrogen atmosphere; gaseous detonation used acetylacetone copper as material, detonated under the negative oxygen conditions with the explosion sources of H2 and O2, H2 and air. The results of XRD, Raman and TEM analyses show that the carbon encapsulated copper nanoparticles with good dispersibility can be obtained by both two detonation methods, and the degree of graphitization of carbon shell is high. Gaseous detonation can synthesize nanocrystals below 10 nm, and the size of nanocrystals by condensed explosives detonation is between 20-40 nm, and there are more empty shells. The gaseous detonation product has a carbon shell size between 2 and 3 nm, and the condensed explosive detonation product has a carbon shell size between 2 and 5 nm.
2017,
29: 084102.
doi: 10.11884/HPLPB201729.170015
Abstract:
The detection and classification of a large number of microspheres is a very important step in inertial confinement fusion experiments. The traditional manual detection and classification method has low efficiency and poor precision, which is difficult to meet the actual needs. This paper proposes a new algorithm of defect detection and classification based on computer vision. After obtaining the image of the microspheres to be measured, the gray histogram is drawn with the inner pixels extracted from the region of interest. Then the cumulative distribution function is calculated, normalized and fitted piecewise and linearly. According to the distribution function after fitting, two parameters, homogeneity and transparency, are proposed to quantitatively express the surface quality of microspheres, and the classification of three types of microspheres, which are smooth, rough and malformed, can be realized. The experimental results show that the accuracy of the proposed algorithm is over 90%. It only takes 300 ms to process an image about 20 microspheres with 1280960 resolution, which is accurate, efficient and extensible.
The detection and classification of a large number of microspheres is a very important step in inertial confinement fusion experiments. The traditional manual detection and classification method has low efficiency and poor precision, which is difficult to meet the actual needs. This paper proposes a new algorithm of defect detection and classification based on computer vision. After obtaining the image of the microspheres to be measured, the gray histogram is drawn with the inner pixels extracted from the region of interest. Then the cumulative distribution function is calculated, normalized and fitted piecewise and linearly. According to the distribution function after fitting, two parameters, homogeneity and transparency, are proposed to quantitatively express the surface quality of microspheres, and the classification of three types of microspheres, which are smooth, rough and malformed, can be realized. The experimental results show that the accuracy of the proposed algorithm is over 90%. It only takes 300 ms to process an image about 20 microspheres with 1280960 resolution, which is accurate, efficient and extensible.
2017,
29: 084103.
doi: 10.11884/HPLPB201729.170054
Abstract:
Accurate high-frequency noise model of nanoscale MOSFET is essential for the low-power design of millimeter-wave integrated circuit. However, the existing high-frequency drain-current noise models do not consider the effect of device substrate and gate resistance, and the dependence of frequency and bias. To solve this problem, based on the physical characteristics of nanoscale MOSFET devices and considering the drift-diffusion equation and the effective gate overdrive, this paper proposes unified drain noise models to characterize the frequency and bias dependence from the strong reverse region to the weak region. The models are effective to the application to advanced design system(ADS) simulation design by predicting the dependency of frequency and bias accurately. The simulation results of the model are compared with the experimental results to verify the accuracy of the model. At the same time, this paper compares the practicability of the models for two different process devices of 130 nm and 40 nm MOSFETs, and verifies that the millimeter-wave noise characteristic of the 40 nm MOSFET is superior.
Accurate high-frequency noise model of nanoscale MOSFET is essential for the low-power design of millimeter-wave integrated circuit. However, the existing high-frequency drain-current noise models do not consider the effect of device substrate and gate resistance, and the dependence of frequency and bias. To solve this problem, based on the physical characteristics of nanoscale MOSFET devices and considering the drift-diffusion equation and the effective gate overdrive, this paper proposes unified drain noise models to characterize the frequency and bias dependence from the strong reverse region to the weak region. The models are effective to the application to advanced design system(ADS) simulation design by predicting the dependency of frequency and bias accurately. The simulation results of the model are compared with the experimental results to verify the accuracy of the model. At the same time, this paper compares the practicability of the models for two different process devices of 130 nm and 40 nm MOSFETs, and verifies that the millimeter-wave noise characteristic of the 40 nm MOSFET is superior.
2017,
29: 085001.
doi: 10.11884/HPLPB201729.170086
Abstract:
This paper present the detailed analysis of the principle of chopper power supply of China Spallation Neutron Source (CSNS ) linear accelerator. The rising edge and the falling edge of the chopped beam bunch are important indexes of the performance of the chopper power supply. Based on the research, a chopper power supply with pulse amplitude of 6 kV and nanosecond grade edge is developed. The method of pure hardware circuit instead of software is used to realize the synchronization and AND processing of high frequency and low frequency signals, which can make the power supply output stable and reliable high voltage pulse. The power supply has two modes (multi pulse and single pulse) to meet the requirements of single beam or multi beam injection into the Rapid Cycling Synchrotron(RCS) ring. The results of the CSNS linac beam chop experiment show that the power supply meets all the design requirements.
This paper present the detailed analysis of the principle of chopper power supply of China Spallation Neutron Source (CSNS ) linear accelerator. The rising edge and the falling edge of the chopped beam bunch are important indexes of the performance of the chopper power supply. Based on the research, a chopper power supply with pulse amplitude of 6 kV and nanosecond grade edge is developed. The method of pure hardware circuit instead of software is used to realize the synchronization and AND processing of high frequency and low frequency signals, which can make the power supply output stable and reliable high voltage pulse. The power supply has two modes (multi pulse and single pulse) to meet the requirements of single beam or multi beam injection into the Rapid Cycling Synchrotron(RCS) ring. The results of the CSNS linac beam chop experiment show that the power supply meets all the design requirements.
2017,
29: 085002.
doi: 10.11884/HPLPB201729.170047
Abstract:
The discharge plasma in the rectangular micro hollow cathode (RMHCD) under high pressure has a multiple negative glow region structure, and the negative glow regions have a tendency of fusion, which can significantly increase the ionization efficiency. The gas is confined in the cavity, which can be effectively heated, and thus can be applied to micro-electric plasma thruster (MPT). In this paper, the 2D x-y cross-section of a rectangular micro-discharge plasma thruster (RMPT) is simulated and analyzed, and a self-consistent fluid model with non-equilibrium state is adopted in the method. The ion current heating and the three-body collision are also considered. The results show that the RMPT has two stable negative glow regions under low current conditions. When a certain current threshold is exceeded, the two negative glow regions will merge at the center of the cavity. Corresponding analysis suggests that the fusion process is essentially a hollow cathode conduction process, whether or not the fusion of negative glow regions occurs is related to sheath voltage.
The discharge plasma in the rectangular micro hollow cathode (RMHCD) under high pressure has a multiple negative glow region structure, and the negative glow regions have a tendency of fusion, which can significantly increase the ionization efficiency. The gas is confined in the cavity, which can be effectively heated, and thus can be applied to micro-electric plasma thruster (MPT). In this paper, the 2D x-y cross-section of a rectangular micro-discharge plasma thruster (RMPT) is simulated and analyzed, and a self-consistent fluid model with non-equilibrium state is adopted in the method. The ion current heating and the three-body collision are also considered. The results show that the RMPT has two stable negative glow regions under low current conditions. When a certain current threshold is exceeded, the two negative glow regions will merge at the center of the cavity. Corresponding analysis suggests that the fusion process is essentially a hollow cathode conduction process, whether or not the fusion of negative glow regions occurs is related to sheath voltage.
2017,
29: 085101.
doi: 10.11884/HPLPB201729.170073
Abstract:
The measurement of electron beam envelope at different position in the anode pipe of injector with a large area thermionic cathode for a linear induction accelerator is very important. It can help to know the emission characteristic of the thermionic cathode for multi pulsed beam and to debug a matched magnetic field for the electron beam transmission in the anode pipe. Dragon-Ⅱ injector adopts a large area thermionic cathode. The period time for heating up or cooling down is very long and the demand of vacuum in the injector is very high especially during operation. It is a problem to destroy the vacuum frequently in order to measure the electron beam envelope in the injector with some ready-made measurement. A multi pulsed electron beam envelope measurement system mainly consists of an extendible and retractile sleeve and a high speed multi framing camera and an optical transition radiation target has been developed to achieve the measurement in the injector without destroying the vacuum. This system can measure envelope at different position in the whole range of the anode pipe and obtain some time-resolved results. This measurement ability has improved greatly the debugging efficiency of Dragon-Ⅱ injector.
The measurement of electron beam envelope at different position in the anode pipe of injector with a large area thermionic cathode for a linear induction accelerator is very important. It can help to know the emission characteristic of the thermionic cathode for multi pulsed beam and to debug a matched magnetic field for the electron beam transmission in the anode pipe. Dragon-Ⅱ injector adopts a large area thermionic cathode. The period time for heating up or cooling down is very long and the demand of vacuum in the injector is very high especially during operation. It is a problem to destroy the vacuum frequently in order to measure the electron beam envelope in the injector with some ready-made measurement. A multi pulsed electron beam envelope measurement system mainly consists of an extendible and retractile sleeve and a high speed multi framing camera and an optical transition radiation target has been developed to achieve the measurement in the injector without destroying the vacuum. This system can measure envelope at different position in the whole range of the anode pipe and obtain some time-resolved results. This measurement ability has improved greatly the debugging efficiency of Dragon-Ⅱ injector.
2017,
29: 085102.
doi: 10.11884/HPLPB201729.170070
Abstract:
There is presently a growing demand for CW high current proton and deuteron linear accelerators based on superconducting technology to better support various fields of science. Up to now, high order modes (HOMs) studies induced by ion beams with current higher than 10 mA and even 100 mA accelerated by low non-elliptical superconducting RF (SRF) cavities are very few. Peking University has recently designed and fabricated a =0.09, 162.5 MHz half wave resonator(HWR) cavity to study the key physics problems in low beta HWR cavity accelerating beam with current of about 100 mA. This paper focuses on the study of the HOM-induced power in this cavity. The incoherent beam energy loss induced by 100 mA beam through the HWR SRF cavity were obtained by both time domain solver and frequency domain eigenmodes spectrum method. The possibility of coherent excitation of this cavity considering manufacture errors was also analysed.
There is presently a growing demand for CW high current proton and deuteron linear accelerators based on superconducting technology to better support various fields of science. Up to now, high order modes (HOMs) studies induced by ion beams with current higher than 10 mA and even 100 mA accelerated by low non-elliptical superconducting RF (SRF) cavities are very few. Peking University has recently designed and fabricated a =0.09, 162.5 MHz half wave resonator(HWR) cavity to study the key physics problems in low beta HWR cavity accelerating beam with current of about 100 mA. This paper focuses on the study of the HOM-induced power in this cavity. The incoherent beam energy loss induced by 100 mA beam through the HWR SRF cavity were obtained by both time domain solver and frequency domain eigenmodes spectrum method. The possibility of coherent excitation of this cavity considering manufacture errors was also analysed.
2017,
29: 085103.
doi: 10.11884/HPLPB201729.170051
Abstract:
In the control system of linear induction accelerator (LIA), Programmable Logic Controller (PLC) is widely used as front end controller in personal protection system (PPS). It is necessary to integrate PLC into input/output controller (IOC) based on EPICS. This paper introduces a new communication method between IOC and PLC based on S7nodave device support and asynchronous communication module, which can achieve the transparent access of IOC to S7 PLC process image area and memory variables without establishing communication buffer, thus keep the independence of the PLC programs. This paper also presents the development procedures and operating interface for PPS.
In the control system of linear induction accelerator (LIA), Programmable Logic Controller (PLC) is widely used as front end controller in personal protection system (PPS). It is necessary to integrate PLC into input/output controller (IOC) based on EPICS. This paper introduces a new communication method between IOC and PLC based on S7nodave device support and asynchronous communication module, which can achieve the transparent access of IOC to S7 PLC process image area and memory variables without establishing communication buffer, thus keep the independence of the PLC programs. This paper also presents the development procedures and operating interface for PPS.
2017,
29: 085104.
doi: 10.11884/HPLPB201729.160527
Abstract:
In high energy flash radiography, the blur is a key problem seriously affecting the accuracy of diagnosis. Due to blurring the detected boundary from the image has a deviation from the true value. The larger the blur size, the larger the boundary deviation with the radiographic layout and the structure of object fixed. On this basis, a new method for determining the blur size of the radiographic system from boundary deviation is presented in this paper. The principle of the method is explained from the physical process of flash radiography. The method is applied to the simulated images, and the measurement of the blur size is validated by means of radiographing the step object. It is shown that the FWHM error of the fuzzy function is less than one pixel, and the backward cone collimator used to photographing the spherical object is recommended.
In high energy flash radiography, the blur is a key problem seriously affecting the accuracy of diagnosis. Due to blurring the detected boundary from the image has a deviation from the true value. The larger the blur size, the larger the boundary deviation with the radiographic layout and the structure of object fixed. On this basis, a new method for determining the blur size of the radiographic system from boundary deviation is presented in this paper. The principle of the method is explained from the physical process of flash radiography. The method is applied to the simulated images, and the measurement of the blur size is validated by means of radiographing the step object. It is shown that the FWHM error of the fuzzy function is less than one pixel, and the backward cone collimator used to photographing the spherical object is recommended.
2017,
29: 085105.
doi: 10.11884/HPLPB201729.160498
Abstract:
According to magnetic field properties and the eddy currents in AC dipole magnet, magnet design and the thermal simulation are performed by the electromagnetic field analysis software and the schemes of key technology are determined. The Rogowski curve and the harmonic chamfering method are applied to improve the magnetic field quality. Slit arrangement on the end plates of the dipole can cut down the eddy currents effectively and lessen the temperature rise. Coils of dipole magnet are made of Al-stranded conductors for the reduction of AC eddy losses. The measurement results and the temperature test of the prototype magnet are described and discussed. The magnetic fields of the prototype meet the requirements and the temperature rise is in the safety range.
According to magnetic field properties and the eddy currents in AC dipole magnet, magnet design and the thermal simulation are performed by the electromagnetic field analysis software and the schemes of key technology are determined. The Rogowski curve and the harmonic chamfering method are applied to improve the magnetic field quality. Slit arrangement on the end plates of the dipole can cut down the eddy currents effectively and lessen the temperature rise. Coils of dipole magnet are made of Al-stranded conductors for the reduction of AC eddy losses. The measurement results and the temperature test of the prototype magnet are described and discussed. The magnetic fields of the prototype meet the requirements and the temperature rise is in the safety range.
2017,
29: 085106.
doi: 10.11884/HPLPB201729.160553
Abstract:
The main Cooling Storage Ring (CSRm) of HIRFL-CSR is used to accumulate, accelerate and extract the charged ion beam to experimental terminal. During accumulation in CSRm, the Multiple Multiturn Injection method with electron cooling is applied at the injection energy to increase beam intensity. Theoretical analysis suggests that the cooling rate and beam lifetime have a strong influence on the beam intensity. On the one hand, electron cooling can quickly shrink the size, divergence and the momentum spread of stored ion beams, which is also used to reduce beam loss caused by Intra Beam Scattering (IBS). On the other hand, the recombination effects between electrons and ions will result in the beam loss. Some experiments on C6+ beam and Ar15+ beam were carried out in CSRm to investigate the relationship between electron cooling and beam lifetime. The beam lifetime was remarkably increased when electron cooling was applied. The effects of the electron beam parameters (density, current, energy and expansion factor) on the ion beam lifetime were measured. The results of the measurement were analyzed based on the electron cooling and recombination theory, and how the electron cooling affect the beam lifetime was studied. According to the measurement results and the analysis, the electron beam parameters were optimized to increase the beam lifetime and the ion beam intensity could be increased to a high level accordingly.
The main Cooling Storage Ring (CSRm) of HIRFL-CSR is used to accumulate, accelerate and extract the charged ion beam to experimental terminal. During accumulation in CSRm, the Multiple Multiturn Injection method with electron cooling is applied at the injection energy to increase beam intensity. Theoretical analysis suggests that the cooling rate and beam lifetime have a strong influence on the beam intensity. On the one hand, electron cooling can quickly shrink the size, divergence and the momentum spread of stored ion beams, which is also used to reduce beam loss caused by Intra Beam Scattering (IBS). On the other hand, the recombination effects between electrons and ions will result in the beam loss. Some experiments on C6+ beam and Ar15+ beam were carried out in CSRm to investigate the relationship between electron cooling and beam lifetime. The beam lifetime was remarkably increased when electron cooling was applied. The effects of the electron beam parameters (density, current, energy and expansion factor) on the ion beam lifetime were measured. The results of the measurement were analyzed based on the electron cooling and recombination theory, and how the electron cooling affect the beam lifetime was studied. According to the measurement results and the analysis, the electron beam parameters were optimized to increase the beam lifetime and the ion beam intensity could be increased to a high level accordingly.
2017,
29: 085107.
doi: 10.11884/HPLPB201729.170080
Abstract:
The optical transition radiation (OTR) shows a distinct directional property with respect to the incident charged particle. The beam divergence angle can be measured by curve fitting of the OTR spatial distribution. The method of theoretical calculation is used to analyze the impact of the variation of the incident angle on the two-dimensional spatial distribution of the OTR when the electron incidents at the metal-dielectric boundary. Theoretical calculations indicate that the OTR distribution in a specific polarization is determined not only by the divergence angle component in the polarization direction but also by that in the perpendicular direction. The difference between the OTR distributions based on one-dimensional modeling and two-dimensional modeling of the divergence angle of the electron beam is calculated. It is demonstrated that the RMS divergence angle of the electron beam based on one-dimensional modeling is generally smaller than that based on two-dimensional modeling.
The optical transition radiation (OTR) shows a distinct directional property with respect to the incident charged particle. The beam divergence angle can be measured by curve fitting of the OTR spatial distribution. The method of theoretical calculation is used to analyze the impact of the variation of the incident angle on the two-dimensional spatial distribution of the OTR when the electron incidents at the metal-dielectric boundary. Theoretical calculations indicate that the OTR distribution in a specific polarization is determined not only by the divergence angle component in the polarization direction but also by that in the perpendicular direction. The difference between the OTR distributions based on one-dimensional modeling and two-dimensional modeling of the divergence angle of the electron beam is calculated. It is demonstrated that the RMS divergence angle of the electron beam based on one-dimensional modeling is generally smaller than that based on two-dimensional modeling.
2017,
29: 086001.
doi: 10.11884/HPLPB201729.160328
Abstract:
Nuclear design and fuel management of submarine reactors and NPP reactors are based on solving 3D multi-group neutron diffusion equation accurately and efficiently. One of the methods for this equation is finite difference method (FDM), which is simple, accurate and mature. However, the computation burden of FDM is huge and the memory requirement is high, thus limiting FDMs scale and application scope. In this paper, FDM for 3D multi-group neutron diffusion equation based on large-scale parallel computation is researched. Mesh-centered FDM is used to discrete the neutron diffusion equation. Large-scale parallel computation is realized by domain decomposition based on MPI, and its accelerated with multi-group multi-domain coupled PGMRES algorithm. ParaFiDi code is developed on high performance cluster and verified by several benchmarks such as IAEA3D and PHWR. Numerical results demonstrate that ParaFiDi code could obtain good efficiency and accuracy.
Nuclear design and fuel management of submarine reactors and NPP reactors are based on solving 3D multi-group neutron diffusion equation accurately and efficiently. One of the methods for this equation is finite difference method (FDM), which is simple, accurate and mature. However, the computation burden of FDM is huge and the memory requirement is high, thus limiting FDMs scale and application scope. In this paper, FDM for 3D multi-group neutron diffusion equation based on large-scale parallel computation is researched. Mesh-centered FDM is used to discrete the neutron diffusion equation. Large-scale parallel computation is realized by domain decomposition based on MPI, and its accelerated with multi-group multi-domain coupled PGMRES algorithm. ParaFiDi code is developed on high performance cluster and verified by several benchmarks such as IAEA3D and PHWR. Numerical results demonstrate that ParaFiDi code could obtain good efficiency and accuracy.
2017,
29: 086002.
doi: 10.11884/HPLPB201729.170057
Abstract:
In order to acquire time resolution image of -ray while impulse pulse width is under 20 ns, a new scintillator named Yb:YAG is developed, and its characteristics of luminescence decay time, excited luminescence spectrum of X-ray, relative luminescence efficiency and spatial resolution are measured. The measurement shows that there are three decay components. The fast decay constant comes to 1.2 ns, but the slow decay constant depends on radiation category. The excited luminescence spectrum ranges from 250 nm to 800 nm, and three peaks, 320 nm, 380 nm, 500 nm, exist. Meanwhile, the strongest intensity spectrum is located at 320 nm. The relative luminescence efficiency reaches 1900 ph/MeV. The spatial resolution is 2 lp/mm in the test with W resolution chart. The frequency is 0.7 lp/mm when the MTF is 0.5 in the test with edge image. The result shows that the characteristics of Yb:YAG crystal could satisfy the measurement demand.
In order to acquire time resolution image of -ray while impulse pulse width is under 20 ns, a new scintillator named Yb:YAG is developed, and its characteristics of luminescence decay time, excited luminescence spectrum of X-ray, relative luminescence efficiency and spatial resolution are measured. The measurement shows that there are three decay components. The fast decay constant comes to 1.2 ns, but the slow decay constant depends on radiation category. The excited luminescence spectrum ranges from 250 nm to 800 nm, and three peaks, 320 nm, 380 nm, 500 nm, exist. Meanwhile, the strongest intensity spectrum is located at 320 nm. The relative luminescence efficiency reaches 1900 ph/MeV. The spatial resolution is 2 lp/mm in the test with W resolution chart. The frequency is 0.7 lp/mm when the MTF is 0.5 in the test with edge image. The result shows that the characteristics of Yb:YAG crystal could satisfy the measurement demand.
2017,
29: 089001.
doi: 10.11884/HPLPB201729.160550
Abstract:
Micro-scale laser shock peening is a surface treatment technology, which utilizes laser pulse with spot-size in micro-scale, low energy and short duration to induce shock wave acting on the metals. In order to improve mechanical properties of DZ17G directionally-solidified alloy without effects on the columnar crystals, micro-scale laser shock peening was suggested. The surface morphology, microstructure and micro-hardness were studied to analyze the effects on surface integrity by X-ray diffractometer, scanning electron microscope, transmission electron microscope and micro-hardness tester. The experiment showed that the alloy surface was ablated and melted by micro-laser shock peening underwater without ablating layer. There was smooth region generated with one laser impact, but the ablation degree increased with laser impacts, generating lots of ablation holes and infusible particles. The material still consisted of phases of and . High-density dislocations and dislocation tangles were generated in material surface after LSP, but without grains refined. The micro-hardness decreased with depth, with an affected depth of 100 m and a maximal value 503 HV in the surface, increased by above 20%, under one laser impact. The micro-hardness and hardened layer depth increased with laser impacts.
Micro-scale laser shock peening is a surface treatment technology, which utilizes laser pulse with spot-size in micro-scale, low energy and short duration to induce shock wave acting on the metals. In order to improve mechanical properties of DZ17G directionally-solidified alloy without effects on the columnar crystals, micro-scale laser shock peening was suggested. The surface morphology, microstructure and micro-hardness were studied to analyze the effects on surface integrity by X-ray diffractometer, scanning electron microscope, transmission electron microscope and micro-hardness tester. The experiment showed that the alloy surface was ablated and melted by micro-laser shock peening underwater without ablating layer. There was smooth region generated with one laser impact, but the ablation degree increased with laser impacts, generating lots of ablation holes and infusible particles. The material still consisted of phases of and . High-density dislocations and dislocation tangles were generated in material surface after LSP, but without grains refined. The micro-hardness decreased with depth, with an affected depth of 100 m and a maximal value 503 HV in the surface, increased by above 20%, under one laser impact. The micro-hardness and hardened layer depth increased with laser impacts.
