A computational and experimental investigation of wall loading near the DITE limiters

Abstract

Recycling, from the DITE fixed limiter has been simulated employing a three-dimensional version of the DEGAS Monte Carlo neutral particle transport code. Experimental plasma data are used for input, in conjunction with a reasonable approximation to the DITE geometry. Between basic cases, moments of the neutral distribution function exhibit a scaling with limiter ion flux which becomes increasingly non-linear with order, a prominent instance being the first wall power loading. This reflects principally the influence of charge exchange neutrals sensing the ion temperature profiles. By also modifying the geometry, the neutral distribution is found for the regime investigated to depend primarily on plasma properties in velocity space and confining geometry in configuration space. On DITE, a so-called “energy sensor array” (ESA) of bolometers detects wall loading adjacent to the limiter directly. Supposing a homogeneous radiation background, the computational model agrees with ESA data roughly within a factor of 2.