射频负离子源中氢负离子产生机制的数值模拟研究

A high energy radio frequency (RF) negative ion source has attracted increasing attention for use in the next generation fusion devices such as the International Thermonuclear Experimental Reactor (ITER). However, there is still a lack of an effective numerical model covering the discharge process, diffusion process, as well as the surface reactions. In this work, a self consistent fluid-Monte Carlo (fluid-MC) hybrid model is developed for the simulation of the Inductively coupled plasma (ICP) negative ion source, which includes the reactor geometry and chemical properties. The emphasis of this project is to investigate the influence of the discharge parameters and reactor geometry on the H negative production and plasma spatial uniformity. In addition, the experimental study is also presented via a newly designed neutral beam ion source. Measurements of the electron density, electron temperature, etc. by Langmuir probe, ICCD and OES are used for the model vertification. The results of this work will be helpful for the designation and optimization of the neutral beam ion sources.

在面向ITER计划的研究工作中，大功率射频(RF)负离子源作为应用于下一代聚变装置的主要中性束离子源得到越来越多的关注。然而目前尚缺乏一个有效的数学模型对射频离子源的放电过程、扩散过程及表面过程进行完整的仿真模拟。本项目将建立一套自洽的流体力学-蒙特卡洛（MC）混合模型，结合实际腔室结构及H2放电物理化学性质对射频感性耦合等离子体(ICP)负离子源放电进行数值模拟研究。通过对射频源参数及腔室结构条件等参数的调节，重点考察其对于氢负离子产额、空间均匀性等方面的影响。同时基于现有的中性束等离子体源装置开展前期实验诊断工作，通过Langmuir探针、ICCD、光谱等检测手段将得到的电子密度、温度等与数值模型进行对比验证。研究结果可以为离子源设计优化等提供一定的参考及解决方案。

本项目主要通过搭建一套2D柱坐标的射频ICP离子源流体仿真模型，研究了H2、He及其混合气体在ICP离子源的放电模式及加热机理，同时采用COMSOL商业软件和实验诊断等手段进行模型验证。在实验方面，搭建了一套大功率中性束离子源及有铯注入的氢负离子源系统，采用Langmuir探针等工具研究了功率、线圈结构、腔室尺寸等参数对放电的影响。对于氢负离子产生机制，提出了新型的射频离子源模型结构，该模型可以有效的避免电子在磁场中的漂移作用而引起的不对称性及束流逸出，有望为下一代的负离子源设计提供可行方案。