Time-resolved measurements of arcing in the DITE tokamak

Abstract

Time-resolved arcs have been observed in the DITE tokamak using three independent techniques, the observation of the current flowing to a probe, the spectral emission from the probe material, and the arc tracks on a rotating disc. The results obtained with the different methods are in good agreement and show that arcing typically occurs in DITE during the first 20 ms of the discharge. This short period of arcing is consistent with measurements of the metal impurity flux at the wall, which show a similar time dependence. Observations of the arc current as a function of radial position show that arcing is negligible 3 cm beyond the radius of the fixed limiter, in good agreement with the observed arc tracks on projecting surfaces of the torus. The erosion of a probe was estimated from the charge flowing in the arcs and is consistent with previous measurements of the metal impurities deposited at the torus wall.