等离子体屏蔽对He2+与H原子碰撞电离微分截面的影响

应用经典径迹Monte Carlo（CTMC）方法研究了He²⁺与H原子在等离子体环境下的碰撞电离过程，计算了在5—400 keV/u的能区随等离子体屏蔽作用变化的碰撞电离总截面和一阶微分截面.等离子体中带电粒子之间的相互作用采用Debye-Hückel模型来描述.由于等离子体屏蔽效应的存在，靶中束缚态电子能级及其经典微正则分布以及入射离子与靶电子的相互作用都发生了变化，而这些变化会直接影响碰撞电离过程.研究发现，碰撞电离总截面随等离子屏蔽的增加而增大，特别是在10 keV/u以下的低能区电离截面有量级的增加.对随能量变化的一阶微分截面，在低能碰撞过程中，屏蔽作用增加，微分截面呈量级增加，高能碰撞微分截面呈倍数增加.同时，屏蔽作用导致电离电子向高能方向移动，随着碰撞能量的增加两体碰撞机制的贡献越来越大，并在较高的出射电子能量出现了一个新的峰.对无屏蔽的自由原子碰撞过程，CTMC方法计算出的电离总截面在碰撞能量大于70 keV/u的较高能区在实验误差内与实验测量结果符合很好，而在较低的能区比实验值小30%—50%. 关键词： 重粒子碰撞电离 等离子体屏蔽效应 经典径迹Monte Carlo方法 Debye-Hückel模型

Plasma screening effect on the differential cross sections of collision ionization of H by He~(2+)

A classical trajectory Monte Carlo method is used to investigate the collision ionization of H by He~(2+) in Debye plasma, and the total and differential cross sections are obtained for collision energies of 5-400 keV/u in a large plasma parameter range. The interaction between charged particles is described by the Debye-Hückel model. Plasma screening changes the ionization energy and classical microcanonical distribution of bound electrons and the interaction between electron and the projectile, which result in the modification of ionization cross sections. It is found that both the total and differential cross sections increase with the increasing of screening interaction, and especially for energies below 10 keV/u, the cross sections are one to two magnitudes larger than those in the unscreened case. The emitted electron moves to the higher energy range, and the binary-encounter ionization mechanism becomes more important and a new hump appears due to the screening effect. Our unscreened cross section is in a good agreement with the experimental measurement for collision energies beyond 70 keV/u.