The ontogeny of a Tokamak discharge

Abstract

A detailed description of the time behaviour of a hydrogen discharge in the ST-Tokamak is based on measured radial electron temperature and density profiles at 12 different times, together with measurements of the Ohmic-heating current and voltage, the temporal, spatial, and spectral distributions of hydrogen light, the ion temperatures, and impurity concentrations. Early in the discharge the electron temperature profiles show evidence of a skin effect that develops on a time-scale of several milliseconds into a peaked profile of about 2.2 keV maximum. Thereafter the peak temperature stops growing and develops into a flat plateau, the width of which appears to be determined by the Kruskal-Shafranov limit. The average particle confinement time scales with , and reaches a maximum of 13-14 ms. The power balance is dominated by electron loss and re-cycling, rather than ion loss or radiation. The recycling process at the aperture limiter appears to involve sufficiently energetic neutral atoms to provide a fairly flat radial source function for particles, and hence to influence directly the development of the radial distribution of power input and energy balance.