EAST辐射偏滤器运行模式下等离子体杂质浓度评估方法

Evaluation of plasma impurity concentration during radiative divertor operation mode on EAST

通过在偏滤器区域充入适量氖气(Ne)或氩气(Ar),东方超环(Experimental Advanced Super-conducting Tokamak,EAST)托卡马克装置实现了辐射偏滤器运行模式。在辐射偏滤器运行模式下,靶板热负荷显著降低,有效缓解了高能粒子流对偏滤器靶板的损伤。但是在偏滤器区域充入过量杂质气体时,杂质粒子会沿着磁力线进入主等离子体,影响主等离子体的约束性能,甚至导致等离子体破裂。因此,有必要研究偏滤器区域等离子体杂质浓度的估算方法,分析充入杂质气体时该区域杂质的定量变化,以此来评估充入的杂质气体对芯部等离子体约束性能的影响。本文针对不同的杂质种类,建立了不同的杂质浓度估算方法。对于钨杂质,通过极紫外光谱(Extreme Ultraviolet Spectroscopy,EUV)诊断系统测量偏滤器区域钨杂质的辐射强度,再根据碰撞-辐射模型对该区域的钨杂质浓度进行了估算。对于Ne杂质,则通过等离子体有效电荷数(Z_(eff))的变化进行了Ne杂质浓度估算。基于估算结果,对辐射偏滤器条件下的芯部杂质行为进行了讨论。上述杂质浓度评估方法对开展辐射偏滤器条件下等离子体约束性能研究,优化辐射偏滤器运行参数有重要意义。

[Background]By injecting gaseous neon(Ne)or argon(Ar)into the divertor region,the radiative divertor operation mode has been successfully realized on experimental advanced superconducting tokamak(EAST).During the radiative divertor operation phase,the damage to divertor plates is effectively mitigated by reducing heat load from high energy particles.However,the injected excess impurity gas may penetrate the last closed flux surface and transport to the core region,causing the degradation of core plasma confinement.[Purpose]This study aims to develop an evaluation method to measure the core impurity concentration for assessment the effects of injected impurity on the confinement of core plasma.[Methods]The absolute intensity of impurity radiation characteristic line was measured and calculated in combination with collisional radiation model(CR model),and different evaluation methods of impurity concentration were developed for different impurity species.The concentration of impurity tungsten(W)was evaluated by combining the radiation intensity measurement from extreme ultraviolet spectroscopy and CR model whilst the concentration of impurity Ne was assessed on the basis of measurement of effective charge number(Zeff).The impurity level in the core region was analyzed in details.[Results]Measurement and model calculation results show that the concentration of Ne and W impurities in the core increases significantly after Ne impurity injected.[Conclusions]The evaluation method in the study is important for evaluating confinement in the core region during radiative divertor and improving plasma performance.