Halo plasma heating by neutral beam injection in TMX‐U

The electron temperature and density of the halo in TMX‐U have been measured by Langmuir probes to study the heating of the halo plasma by neutral beam injection. This study is motivated by the recent interest in using a pair of halo recyclers to enhance the halo density and thereby increase halo shielding. In present TMX‐U operation, without halo recyclers, a halo density of 2×1012 cm−3 with electron temperature of 20 eV has been measured during the heating phase with neutral beam injection only. A halo power balance model incorporating several heating mechanisms resulting from neutral beam injection is described. The model accurately predicts the measured temperatures. At the halo density range that one expects to achieve with halo recyclers, the model predicts the existing TMX‐U neutral beam sources to heat the halo to at least 30 eV.