Investigations of the start up phase in the TM 1 tokamak

The avalanche phase of the plasma discharge in the TM-1-MH tokamak was investigated. Basic parameters of the discharge, the position of the plasma ring, and Langmuir probe characteristics were measured. Following experimental results, the plasma density increases exponentially during the initial stage, the time constant being determined by the balance between carrier production and losses. Carrier production is controlled by the electron drift in the toroidal electric field and not by thermal ionization. Carrier losses are determined by auxiliary perpendicular magnetic fields and by internal fields caused by various imperfections of the tokamak geometry. A theoretical model describing electrodynamical properties of the avalanche phase of the discharge was set up. The model makes it possible to calculate important plasma parameters from simple measurements of loop voltage and plasma current. The calculated values are in good agreement with experimental data. (J.U.)