EAST上中性束注入和离子回旋共振加热下快离子分布函数层析反演

Tomography of fast ion distribution function under neutral beam injection and ion cyclotron resonance heating on EAST

聚变等离子体中快离子分布函数的速度空间层析反演(tomography)是研究磁约束核聚变装置中快离子分布和输运的重要手段.在东方超环(experimental advanced superconducting tokamak,EAST)中性束注入(neutral beam injection,NBI)与离子回旋共振加热(ion cyclotron range of frequencies heating,ICRF)协同加热实验中,快离子诊断测量信号以及TRANSP模拟获得的快离子分布函数中观测到协同效应产生的高于中性束注入能量的高能粒子.为了研究快离子分布行为,获得不同加热条件下诊断测量的快离子分布函数,采用不同的正则化方法,增加先验信息以及将快离子D_(α)光谱诊断(fast-ion D_(α)spectroscopy,FIDA)与中子发射谱仪(neutron emission spectrometers,NES)相结合等方式,有效提高快离子诊断信噪比以及在速度空间权重覆盖率,实现在单独NBI加热以及NBI和ICRF协同加热条件下基于诊断测量的层析反演,获得真实可靠的快离子分布函数.这为下一步提高NBI与ICRF协同加热效率,研究协同加热机制以及相关的快离子分布和输运行为奠定基础.

In magnetic confinement fusion devices,velocity-space tomography of fast-ion velocity distribution function is crucial for investigating fast-ion distribution and transport.In the neutral beam injection(NBI)and ion cyclotron resonance heating(ICRF)synergistic heating experiments in Experimental Advanced Superconducting Tokamak(EAST),high-energy particles with energy exceeding the particle energy in NBI are observed.Simulations of synergistic effect on fast-ion velocity distribution function given by TRANSP also show the existence of particles with energy higher than the particle energy in NBI.To investigate the behaviors of fast ion distribution and calculate the velocity distribution functions under different heating conditions,the first-order Tikhonov regularization tomographic inversion method with higher inversion accuracy is introduced by comparing various regularization techniques.The limitations of the dual-view fast-ion D_(α)(FIDA)diagnostic measurements in velocity space are addressed by incorporating prior information such as null measurement and the known peaks and effectively mitigate the occurrence of artifacts.This method is first employed in the case of NBI heating.The NBI peak is successfully reconstructed at the expected location in velocity space,which shows significant improvement in the inversion results.In order to further validate the synergistic effect of NBI-ICRF heating and study the mechanism of fast ion distribution under synergistic heating,the combination of FIDA and neutron emission spectrometer(NES)is applied to the first-order Tikhonov regularization tomographic inversion method for enhancing the coverage of velocity space,through which the issue of artifacts in the inversion results is significantly improved,and thus the precision of the obtained fast-ion velocity distribution functions is enhanced.Based on the benefit described above,the method of combining NES diagnosis and FIDA diagnosis is used to obtain fast-ion velocity distribution functions in the NBI and ICRF synergistic heating discharge.The synergistic heating effect is manifested in the fast-ion velocity distribution.The availability of this inversion method in reconstructing fast-ion velocity distribution functions during high-performance operation of NBI-ICRF synergistic heating in the EAST experiment is confirmed.In the next-step EAST research,high performance discharge will demand more efficiency NBI and ICRF synergistic heating,the present work builds the stage for investigating the underlying mechanism of synergistic heating and the intricate behaviors associated with fast ion distribution and transport.