Helium Transport and Exhaust Studies in the TEXTOR Tokamak

The charge exchange spectroscopic system for TEXTOR provides absolute helium(He) density profiles at 15 spatial locations along the plasma minor radius. Helium transport and exhaust measurements have been made for L-mode discharges as a function of plasma current, neutral beam power, and electron density. Experiments have also been carried out in I-mode discharges with a radiating Ne boundary. After the introduction of helium into the discharge via a gas puff, the total helium inventory is followed from the core (charge exchange spectroscopy) to the edge (emission spectroscopy) and into the ALT-II pumping plenum (modified Penning gauge). From these data the He recycling and transport coefficients (anomalous diffusivity, pinch velocity) are obtained from modeling with a multispecies impurity transport code. Comparisons have been made between the results and various L-mode scaling laws (ITER-89P, Taroni-Jet, Tore Supra-JET). For a typical discharge, the value of τ^*_He/τ_E is about 15.