Plasma Shaping by Control of Plasma Current, Decay Index and Gas Puffing in Non-Circular Tokamak TNT-A

Abstract

In the non-circular tokamak TNT-A, we have tried to elongate plasma column by the combined operation of rapid rise of plasma current and rapid decrease in the decay index n (=−(R⁄B_z)·(∂B_z⁄∂R)) with gas puffing after the current establishment. The increase in elongation ratio is obtained without deleterious effects on MHD instabilities. Dependence of elongation ratio on plasma parameters is calculated and compared with measurements. The growth rate of positional instabilities in the vertical direction is measured as a function of the decay index, and has good agreement with a calculation.