摘要
偶极磁场约束等离子体特性及其与带电粒子束的相互作用研究是近地空间磁层等离子体研究领域关心的一类重要问题.本研究采用粒子模拟(particle in cell, PIC)方法,通过开源的Smilei程序,研究了电子束注入偶极磁场约束等离子体的三维动力学演化行为.模拟了不同注入角度电子束对等离子体的影响,给出了电子束及等离子体的时空演化过程和行为解释.结果显示,偶极磁场中的等离子体沿磁场线形成“新月形”壳结构分布,壳中形成内外相反方向的环形电流.当电子束的注入角度与磁场方向的夹角过大(超过20°),且漂移速度方向未对准偶极场中心时,大多数电子束粒子将在偶极磁场中漂移,散射并弹出模拟区域,无法与偶极磁场约束的等离子体发生相互作用.未来我国的偶极磁场约束等离子体研究装置在开展电子束与等离子体相互作用的实验时,有必要选择适当的电子束入射方向,以确保电子束能够进入偶极磁场的核心区域并与原来约束的等离子体进行相互作用.同时模拟结果显示电子束注入会使得等离子体环形电流在环向上变得不均匀.本研究有助于深入了解偶极磁场中的等离子体动力学行为特性,对于保障我国空间等离子体研究装置完成预期科学目标具有实际价值.
Research into the characteristics of dipole magnetic field-confined plasmas and their interaction with charged particle beams is critical for understanding near-Earth magnetospheric plasma.In this paper,a fully relativistic electromagnetic particle-in-cell(PIC)method,implemented with the open-source code Smilei,is used to perform three-dimensional kinetic simulations of the evolution of electron beams injected into the dipole magnetic field confined plasmas.The simulation adopts a uniform grid with 256 cells in each spatial direction,neglects collisional effects,and considers a plasma consisting only of electrons and ions.The initial plasma with a number density of 1×1012 m–3 is configured as a rectangular toroidal structure with a square cross-section.An externally prescribed dipole magnetic field is applied to the simulation domain.This field is generated by an ideal current loop centered in the grid’s x-y plane,with a loop radius of 1/8 the grid length a current magnitude of 4000 A,and a maximum magnetic field strength of 6000 G.Under these conditions,the ratio of electron plasma frequency to gyrofrequency ranges from 5.3×10–4 to 3.2,and the plasma beta varies from 2.24×10–10 to 8×10–3.The grid cell size is set to 0.05 times the electron Debye length,and the time step is 0.95 times the CFL time step.The simulation runs for a total of 20000 steps to achieve a quasi-steady state.The electron beams with a temperature of 10 eV and a drift velocity of 1×107 m/s are injected from the x-min boundary of the grid at angles of 0°,30°,and 60°relative to the positive x-axis,to explore the influence of electron beams with varying injection angles on the dipole magnetic field confined plasma.The simulation results demonstrate the spatiotemporal evolution and behavior of the electron beam and plasma.Specifically,the plasma confined by a dipole magnetic field forms a crescent-shaped shell structure that aligns with magnetic field lines,with toroidal currents of opposite directions generated inside and outside the shell.When the electron beam is injected at incident angles of 0°and 30°,drift effects cause most of beam particles to concentrate along a specific magnetic field line on the x+y=250△x plane.Additionally,the drift current induced by electron beam injection changes the distribution of the central toroidal current in the main plasma,resulting in localized enhancement and attenuation of the toroidal current.In contrast,at an injection angle of 60°,the vast majority of beam particles are scattered by the dipole magnetic field,and fail to reach the central region to interact with the main plasma.Simulation findings further indicate that when the electron beam’s injection angle relative to the magnetic field direction exceeds 20°and its drift velocity is misaligned with the dipole field center,most of beam particles scatter and are ejected from the simulation domain,precluding interaction with the dipole-confined plasma.For future experimental devices studying the interactions between electron beam and plasma in dipole magnetic field confinement systems,choosing an appropriate beam injection direction is critical to ensure that the electrons can reach the core region of the dipole field and interact with the confined plasma.This study offers valuable insights into the dynamic behavior of plasma in dipole magnetic fields,aiding space plasma research facilities in achieving their designed scientific objectives.
作者
潘宇浩
王志斌
†陈坚
叶卓晖
易祖宁
肖青梅
毛傲华
张仲麟
聂秋月
PAN Yuhao;WANG Zhibin;CHEN Jian;YE Zhuohui;YI Zuning;XIAO Qingmei;MAO Aohua;ZHANG Zhonglin;NIE Qiuyue(Sino-French Institute of Nuclear Engineering and Technology,Sun Yat-sen University,Zhuhai 519082,China;State Key Laboratory of Space Environment Interaction with Matters,Harbin Institute of Technology,Harbin 150001,China;School of Electrical Engineering and Automation,Harbin Institute of Technology,Harbin 150001,China)
出处
《物理学报》
北大核心
2025年第23期225-238,共14页
Acta Physica Sinica
基金
国家自然科学基金(批准号:12175322,12305223)资助的课题。
关键词
等离子体
电子束
偶极磁场
粒子模拟
plasma
electron beam
dipole magnetic field
particle-in-cell
