离子束中性化过程中静电孤波激发和抑制的实验与数值模拟研究

离子束中性化在重离子聚变束物理、离子束表面工程、空间电推进等领域有广泛应用，如何提高中性化率是一个重要物理问题。最近我们同合作者通过数值模拟首次发现，当中性化方式采用电子直接注入或者短等离子体源注入时，中性化过程中会激发长寿命、大尺度静电孤波（ESWs）。ESWs的激发大幅度降低这两种中性化方法的中性化率。本项目计划通过实验来验证中性化过程ESWs激发的可能性。首先通过实验诊断中性化过程中ESWs双极性特征电脉冲信号，研究ESWs激发条件和机制，获得ESWs纵向尺度、电场强度、寿命、运动速度等基本参数；然后通过束测给出离子束的中性化率，评估ESWs的激发对中性化的影响；最后通过实验研究ESWs的抑制方法。除了实验，项目计划通过自编三维并行PIC程序对上述实验进行数值模拟，重点研究中性化过程中电子动理学过程以及ESWs的激发和抑制机制。本项目的实施将为提升离子束中性化率提供全新的思路和策略。

Ion beam neutralization has been widely studied in heavy ion fusion beam physics, ion beam surface engineering, and space electric propulsion, etc. How to increase the degree of ion beam neutralization is a critical physical issue. Recently we've discovered with our collaborator through numerical simulations that, when electron direct injection or short plasma source injection is applied as a neutralization scheme, long-lived and large-amplitude electrostatic solitary waves (ESWs) can be excited during neutralization. The excitation of ESWs dramatically reduces the degree of neutralization of these two schemes. This project is planned to verify the possibility of excitation of ESWs during neutralization through experiments. Firstly, we will diagnose experimentally the bipolar characteristic pulse signals of ESWs, and study the excitation conditions and mechanisms of ESWs, obtaining ESWs basic parameters such as the longitudinal size, the intensity of electric field, the lifetime and the velocity of motion. Secondly, through beam measurements, the degree of neutralization of the ion beam will be given, and the effect of excitation of ESWs on neutralization will be evaluated. Finally, the suppression method of ESWs will be studied experimentally. Besides experiments, in this project we plan to simulate these experiments numerically through a self-made 3D parallel PIC code, focusing on the kinetic process of neutralizing electrons and the excitation and suppression mechanism of ESWs during neutralization. The implementation of this project will provide some totally new ideas and strategies to improve the degree of neutralization of the ion beam.