EXL-50U球形环中快离子磁场波纹损失的优化模拟研究

Optimizing numerical simulation of beam ion loss due to toroidal field ripple on EXL-50U spherical torus

EXL-50U装置高参数等离子体的实现对中性束注入(NBI)加热的依赖非常敏感,期望NBI快离子约束良好并通过碰撞慢化把能量传给背景等离子体.本文基于集成模拟给出的平衡位形、快离子分布和装置波纹度数据对快离子波纹损失开展了模拟研究.发现快离子波纹损份额约为37%,局域热斑约0.6 MW/m2,对装置实验运行来说不可接受.其优化方案包括移动等离子体位置和加FI(铁素体钢插件)降低波纹度,增大I_(p)(等离子体电流)以及优化NBI角度.结果显示必须控制波纹度分布且增大I_(p)到600 kA以上,才能使快离子损失降低到3%-4%,局域热斑降低一个量级.本文总结了装置设计时快离子波纹损失评估的方法,包括相空间快离子分布和波纹损失区重合度,全要素慢化时间尺度粒子跟踪.还总结了降低波纹损失的工程和物理途径,为集成模拟迭代优化和装置运行提供模拟支持。

Realization of high performance plasma of EXL-50U is very sensitive to NBI(neutral beam injection)heating,and it is expected that the fast ions of NBI are confined well and their energy is transferred to the background plasma by collision moderating.In this paper,the loss of fast ion ripple is simulated based on the equilibrium configuration,fast ion distribution and device waviness data given by the integrated simulation.It is found that the loss fraction of fast ion ripple is about 37%,and the local hot spot is about 0.6 MW/m2,which is unacceptable for the experimental operation of the device.The optimization method includes moving the plasma position and adding FI(ferritic steel plug-in)to reduce the ripple degree,increasing the I_(p)(plasma current)and optimizing the NBI injection angle.The results show that the ripple distribution must be controlled and the I_(p)must be increased to more than 600 kA,so that the fast ion loss can be reduced to 3%−4%and the local heat spot can be reduced by an order of magnitude.In this paper,the evaluation methods of fast ion ripple loss in device design are summarized,including the fast ion distribution in phase space,the overlap degree of ripple loss area,and the particle tracking on the time scale of total factor slowing down.The engineering and physical ways to reduce ripple loss are also summarized to provide simulation support for integrated simulation iterative optimization and plant operation.