This study deals with the comparison of impurity behaviour in pellet and gas fuelled JET-ITER like wall pulses with the aim of finding the mechanisms leading to the generally observed higher concentration of tungsten in pellet fuelled plasmas. In fact, tungsten is the main high-Z impurity in the JET-ILW plasmas and is responsible for most of the radiative losses in the plasma core. Analysis of the experimental data pertaining to pulses at different plasma currents, different input power and different electron densities is integrated by numerical modelling with the self-consistent fluid transport code COREDIV. Experimentally, and numerically, the ratio between the radiated power in the divertor and the total one—which results to be an increasing function of the ratio of the electron density at the strike point to the volume average one—is found to be a critical parameter determining impurity accumulation. The higher this value the lower the impurity density in the plasma core. Together with a little higher core impurity residence time, the numerical modelling indicates that the modest divertor screening for the pellet fuelled pulses at low electron flow—characterized by low electron density at the strike point and low perpendicular transport in the SOL—leads to divertor impurity leakage and higher impurity fluxes through the separatrix, in agreement with theory.

本研究涉及颗粒和气体燃料 JET-ITER 壁脉冲中杂质行为的比较，目的是找到导致通常观察到的颗粒燃料等离子体中钨浓度较高的机制。事实上，钨是主要的高ZJET-ILW 等离子体中的杂质，是等离子体核心中大部分辐射损耗的原因。与不同等离子体电流、不同输入功率和不同电子密度下的脉冲有关的实验数据的分析通过数值建模与自洽流体传输代码 COREDIV 进行整合。从实验上和数值上，偏滤器中的辐射功率与总辐射功率之间的比率——结果是撞击点电子密度与体积平均密度的比率的递增函数——被发现是一个关键参数确定杂质积累。该值越高，等离子体核心中的杂质密度越低。再加上稍高的核心杂质停留时间，