多道电子束流能谱描迹仪

介绍了用一种多条金属靶传感器测量直线加速器电子束流能谱的方法 ,主要讨论其原理和电路设计时应考虑的问题     

Numerical simulation of inducing characteristics of high energy electron beam plasma for aerodynamics applications

The problem of flow active control by low temperature plasma is considered to be one of the most flourishing fields of aerodynamics due to its practical advantages.Compared with other means,the electron beam plasma is a potential flow control method for large scale flow.In this paper,a computational fluid dynamics model coupled with a multi-fluid plasma model is established to investigate the aerodynamic characteristics induced by electron beam plasma.The results demonstrate that the electron beam strongly influences the flow properties,not only in the boundary layers,but also in the main flow.A weak shockwave is induced at the electron beam injection position and develops to the other side of the wind tunnel behind the beam.It brings additional energy into air,and the inducing characteristics are closely related to the beam power and increase nonlinearly with it.The injection angles also influence the flow properties to some extent.Based on this research,we demonstrate that the high energy electron beam air plasma has three attractive advantages in aerodynamic applications,i.e.the high energy density,wide action range and excellent action effect.Due to the rapid development of near space hypersonic vehicles and atmospheric fighters,by optimizing the parameters,the electron beam can be used as an alternative means in aerodynamic steering in these applications.     

Focusing characteristics of the relativistic electron beam transmitting in ion channel

Based on the beam–plasma system model established in this paper, the trajectory of the electron beam in the ion channel is studied quantitatively through the envelope equation. Under different initial system parameters, the focusing transmission conditions of the beam in the ion channel are discussed. Then, a series of particle-in-cell simulations are performed, which generally versifies the theoretical results and shows some further details of the focusing behavior of the beam. It is found that the deceleration of some electrons around the focusing point or the beam–plasma interaction at the ion channel boundary will result in the generation of the residual electrons,which forms the electron return current that leads to the new instabilities influencing the focusing characteristics of the beam.     

High energy electron beam generation during interaction of a laser accelerated proton beam with a gas-discharge plasma

The study of the interaction between ion beam and plasma is very important to the areas of inertial fusion energy and high energy density physics. With detailed one-dimensional electromagnetic particle-in-cell simulations, we investigate here the interaction of a laser-accelerated proton beam assuming an ideal monoenergetic beam with a gas-discharge plasma. After the saturation stage of the two-stream instability excited by the proton beam, significant high energy electrons are observed, with maximum energy approaching 2 MeV, and a new two-stream instability occurs between the high energy electrons and background electrons. The trajectories of plasma electrons are studied, showing the process of electron trapping and de-trapping from the wakefield.     

一种测量辐射加工用加速器电子束能量的方法

根据射程法原理,在上海二级标准剂量学实验室对辐射加工用加速器电子束能量的测量方法进行了实验研究,并在3个辐射工厂对3台3MeV、20mA高频高压型加速器的电子束进行了能量测定.结果表明,在1-3MeV能量范围内,能量测定准确度优于±10%.     

A simulated plasma disruption experiment using an electron beam as a heat source

An experimental study was made on the behavior of a solid surface subjected to an extremely high heat flux similar to that expected during a plasma disruption. An electron beam was used as the heat source to simulate the high heat flux. The beam was defocused in an attempt to give as much uniform heat flux as possible on the test surface. The 5-mm-diameter test pieces were made of 304 stainless steel, aluminum, and zinc. Heat fluxes from 10 to 110 MW/m² were applied on the test pieces for durations of 90 to 180 msec. Special attention was paid to the measurement of the surface heat flux on the test surface. Comparison between experimental and analytical results on melt layer thickness and evaporation loss is made. An improved thermal analysis code (DAT-K) was developed for the analysis. Agreement between the experimental and analytical results on melt layer thickness is good. For evaporation loss, experimental and analytical results are in fair agreement. Features of the experiments and analysis that lead to the differences in the results are discussed.On leave from Kawasaki Heavy Industries, Ltd.     

计算脉冲电子束辐照下能量沉积剖面的新方案

脉冲电子束辐照材料试验研究中,束流电子具有不同的速度和角度分布。但数值模拟计算一般都考虑电子束垂直入射靶材料,这可能导致数值计算结果与试验结果不符。针对该问题,提出了一种计算电子束辐照下能量沉积剖面的新方案,利用MCNP(Monte Carlo N Particle Transport Code)软件对铝、铜、钽金属材料在电子束辐照下的能量沉积进行模拟,分析了电子束垂直入射与带有角度分布入射时能量沉积的差异,为解释电子束辐照试验测量数据与理论计算结果之间的差异提供了依据。     

Development and performance characterization of a compact plasma focus based portable fast neutron generator

The design details and performance characterization results of a newly developed plasma focus based compact and portable system (0.5 m × 0.5 m × 1.2 m, weighing ≈100 kg) that produces an average neutron yield of ~2 × 10⁸ neutrons/shot (of fast D-D neutrons with typical energy ~2.45 MeV) at ~1.8 kJ energy discharge are reported. From the detailed analysis of the experimental characterization and simulation results of this system, it has been conclusively revealed that specifically in plasma focus devices with larger static inductance: (i) pinch current is a reliable and more valid neutron yield scaling parameter than peak current, (ii) the ratio of pinch/peak current improves as static inductance of the system reduces, (iii) the benign role of the higher static/pinch inductance ratio enables the supply of inductively stored energy in densely pinched plasma with a larger time constant and it is well depicted by the extended dip observed in the discharge current trace, (iv) there is the need to redefine existing index values of the pinch (Ipinch ^4.7) and peak (Ipeak ^3.9) currents in neutron yield scaling equations to higher values.     

Influence of two-stream relativistic electron beam parameters on the space-charge wave with broad frequency spectrum formation

We developed a cubic non-linear theory describing the dynamics of the multiharmonic spacecharge wave (SCW),with harmonics frequencies smaller than the two-stream instability critical frequency,with different relativistic electron beam (REB) parameters.The self-consistent differential equation system for multiharmonic SCW harmonic amplitudes was elaborated in a cubic non-linear approximation.This system considers plural three-wave parametric resonant interactions between wave harmonics and the two-stream instability effect.Different REB parameters such as the input angle with respect to focusing magnetic field,the average relativistic factor value,difference of partial relativistic factors,and plasma frequency of partial beams were investigated regarding their influence on the frequency spectrum width and multiharmonic SCW saturation levels.We suggested ways in which the multiharmonic SCW frequency spectrum widths could be increased in order to use them in multiharmonic two-stream superheterodyne free-electron lasers,with the main purpose of forming a powerful multiharmonic electromagnetic wave.     

Analysis of the characteristics of the plasma of an RF driven ion source for a neutral beam injector

A radio frequency(RF)driven ion source is a very important component of a neutral beam injector for large magnetic confinement fusion devices.In order to study the key technology and physics of an RF driven ion source for a neutral beam injector in China,an RF ion source test facility was developed at the Institute of Plasma Physics,Chinese Academy of Sciences.In this paper,a two-dimensional fluid model is used to simulate the fundamental physical characteristics of RF plasma discharge.Simulation results show the relationship of the characteristics of plasma(such as electron density and electron temperature)and RF power and gas pressure.In order to verify the effectiveness of the model,the characteristics of the plasma are investigated using a Langmuir probe.In this paper,experimental and simulation results are presented,and the possible reasons for the discrepancies between them are given.This paper can help us understand the characteristics of RF plasma discharge,and give a basis for further R&D for an RF ion source.     

Measurement of time-varying electron density of the plasma generated from a small-size cylindrical RDX explosion by Rayleigh microwave scattering

It is challenging to measure the electron density of the unsteady plasma formed by charged particles generated from explosions in the air, because it is transient and on a microsecond time scale. In this study, the time-varying electron density of the plasma generated from a small cylindrical cyclotrimethylenetrinitramine(RDX) explosion in air was measured, based on the principle of microwave Rayleigh scattering. It was found that the evolution of the electron density is related to the diffusion of the detonation products. The application of the Rayleigh microwave scattering principle is an attempt to estimate the electron density in explosively generated plasma. Using the equivalent radius and length of the detonation products in the bright areas of images taken by a high-speed framing camera, the electron density was determined to be of the order of 10~(20) m~(-3). The delay time between the initiation time and the start of variation in the electron-density curve was 2.77–6.93 μs. In the time-varying Rayleigh microwave scattering signal curve of the explosively generated plasma, the electron density had two fluctuation processes. The durations of the first stage and the second stage were 11.32 μs and 19.20 μs,respectively. Both fluctuation processes increased rapidly to a peak value and then rapidly attenuated with time. This revealed the movement characteristics of the charged particles during the explosion.     

Development of vacuum ultraviolet spectroscopy for measuring edge impurity emission in the EAST tokamak

The dominant wavelength range of edge impurity emissions moves from the visible range to the vacuum ultraviolet(VUV) range, as heating power increasing in the Experimental Advanced Superconducting Tokamak(EAST). The measurement provided by the existing visible spectroscopies in EAST is not sufficient for impurity transport studies for high-parameters plasmas. Therefore, in this study, a VUV spectroscopy is newly developed to measure edge impurity emissions in EAST. One Seya-Namioka VUV spectrometer(McPherson 234/302) is used in the system, equipped with a concave-corrected holographic grating with groove density of 600 grooves mm~(–1). Impurity line emissions can be observed in the wavelength range ofλ=50–700 nm, covering VUV, near ultraviolet and visible ranges. The observed vertical range is Z=-350–350 mm. The minimum sampling time can be set to 5 ms under full vertical binning(FVB) mode. VUV spectroscopy has been used to measure the edge impurity emission for the 2019 EAST experimental campaign. Impurity spectra are identified for several impurity species, i.e., lithium(Li), carbon(C), oxygen(O), and iron(Fe). Several candidates for tungsten(W) lines are also measured but their clear identification is very difficult due to a strong overlap with Fe lines. Time evolutions of impurity carbon emissions of CII at 134.5 nm and CIII at97.7 nm are analyzed to prove the system capability of time-resolved measurement. The measurements of the VUV spectroscopy are very helpful for edge impurity transport study in the high-parameters plasma in EAST.     

Development of a fast electron bremsstrahlung diagnostic system based on LYSO and silicon photomultipliers during lower hybrid current drive for tokamak

A novel real time fast electron bremsstrahlung (FEB) diagnostic system based on the lutetium yttrium oxyorthosilicate scintillators (LYSO) and silicon photomultipliers (SiPM) has been developed for tokamak. The diagnostic system is dedicated to study the FEB emission in the hard x-ray (HXR) energy range between 10 and 200 keV during the lower hybrid current drive. The system consists of a detection module and three data acquisition and processing (DAP) boards. The detection module consists of annulus LYSO-SiPM detector array and a 12-channel preamplifier module. The DAP boards upload the data to the host computer for displaying and storing through PXI bus. The time and space resolutions of the system are 10 ms and 4cm, respectively. The experimental results can show the evolution over time and the spatial distribution of FEB. This paper presents the system performance and typical discharge results.     

ADS核数据实验测量装置建设及首次测试实验

介绍了基于我国大科学实验装置兰州重离子加速器冷却储存环(HIRFL-CSR)的加速器驱动的次临界系统(ADS)相关核数据实验测量装置建设及首次测试实验。该实验装置探测系统主要包括束流拾取探测器、轻带电粒子谱仪、γ探测器阵列及中子飞行时间谱仪。为了对该实验装置各探测器及相配套的电子学与数据获取系统进行整体性能测试,利用400MeV/u 16 O轰击Pb靶,对出射的中子、γ射线及轻带电粒子等产物的能谱、产额及角分布等物理量进行测量,在国内首次实现了加速器驱动的几MeV至几百MeV宽能量范围的白光中子能谱测量。实验结果表明,该实验装置运行正常,实验方案可靠、正确。     

Exploration of a MgO cathode for improving the intensity of pulsed discharge plasma at atmosphere

With regard to the lower density and energy of electrons in pulsed discharge plasma (PDP) at atmosphere, leading to the lower energy utilization of plasma, we propose a MgO cathode to enhance the plasma intensity according to field emission principle. The MgO cathode is prepared by an electro-depositing MgO film on a stainless steel plate. This way, the positive charges come to the cathode and accumulate on the surface of the MgO film, leading to the enhancement of the electric field intensity between the cathode and MgO film, and result in the strong emission of secondary electrons from the MgO cathode. As a result, the intensity of plasma can be enhanced. Herein, the effect of the MgO cathode on the intensity of PDP is investigated. It was shown that the discharge peak current was improved by 20% compared with that of without the MgO cathode. With increasing the MgO film thickness, discharge intensity, including the peak current, transforming charge and spectrum intensity first increased and then decreased. Higher enhancement of peak current, transforming charge and spectrum intensity were acquired with a higher peak voltage. Compared to a cathode without MgO film, the ozone production is higher with MgO cathode employed. The research proposes a novel approach for improving the intensity of discharge plasma, and also provides a reference for further application of PDP.     

Development of a method for measuring the ortho-positronium quenching rate in low vapor-pressure gases

A new measurement and analysis method for determining the ortho-positronium collisional quenching rate for low vapor-pressure gases is developed. It uses hydrophobic silica aerogels as highly efficient positronium formation media and microchambers. The value of the normalized positronium quenching rate, ¹Z_eff, for CH₃Br measured by this method is 0.70 ± 0.04.