电子束透射氮化硅薄膜窗产生低密度等离子体  

Low-density plasmas generated by electron beams passing through silicon nitride window

作　　者：颜劭祺 高继昆 陈越 马尧 朱晓东 Yan Shao-Qi;Gao Ji-Kun;Chen Yue;Ma Yao;Zhu Xiao-Dong(School of Physical Sciences,University of Science and Technology of China,Hefei 230026,China)

机构地区：[1]中国科学技术大学物理学院,合肥230026

出　　处：《物理学报》2024年第14期61-67,共7页Acta Physica Sinica

基　　金：国家重点研发计划(批准号:2018YFE0301102)资助的课题.

摘　　要：低电子密度等离子体源在电离层等离子体的实验室模拟中具有重要的应用.本文利用高能电子束透射氮化硅薄膜窗口,在低气压条件下激发低密度等离子体.采用蒙特卡罗方法对氮化硅薄膜的电子束透射特性进行模拟;利用CCD相机和静电探针对产生的电子束等离子体进行诊断.电子束等离子体呈现出顶点位于氮化硅薄膜窗口的锥状结构.在相同气压下,电子初始能量越高,锥状等离子体锥角越小,等离子体更加向轴线集中,这与氮化硅薄膜的电子透射特性蒙特卡罗模拟定性一致.随着工作气压增大,高能电子与中性粒子碰撞频率变大,电子束散射效应增强导致等离子体锥角变大.等离子体锥状结构是高能电子透射特性以及高能电子与气体分子散射特征的反映.在40 keV条件下,当电子束流从10μA减小到0.5μA时,电子密度减小,变化在10^(5)—10^(6) cm^(-3)范围;而电子温度没有明显的变化,接近1 eV.随气压增大,电子密度有增大趋势.研究工作表明,在工作腔尺寸足够大的情况下,可得到沿电子入射方向随距离增加逐渐衰减的10^(5) cm^(-3)以下更低的电子密度;这是由于射程增加,透射的高能电子与中性气体碰撞产生能量损失增大;同时电子束散射增强导致了等离子体更加发散.In general,more attention is paid to how to improve the characteristic parameters of plasma in plasma applications.However,in some cases,it is necessary to produce plasma with low-electron density,such as in the laboratory simulation of ionospheric plasma in space science.In this study,a low-density plasma is generated by electron beams passing through a silicon nitride transmission window under low pressure condition.The transmission properties of electron beam passing through silicon nitride films are investigated by Monte Carlo simulation,and the plasma feature is studied by a planar Langmuir probe and a digital camera.It is found that the plasma exhibits a conical structure with its apex located at the transmission window.At a constant pressure,the cone angle of conical plasma decreases with the electron energy increasing.This is qualitatively consistent with the Monte Carlo simulation result.The frequency of electron-neutral collisions increases as the working pressure rising,which leads the plasma cone angle to increase.When the beam current is reduced from 10μA to 0.5μA at 40 keV,the electron density decreases,in a range between 10^(5) and 10^(6) cm^(–3),while the electron temperature does not change significantly but approaches 1 eV.It can be inferred that the electron density decreases with the distance z from the transmission window in the incident direction of the electron beam.A low-density plasma of less than 10^(5) cm^(–3) can be obtained further away from the transmission window.

关 键 词：电子束 等离子体产生 等离子体源 电子密度 

分 类 号：O53[理学—等离子体物理]