Discharges with Reduced-Volume Plasma Filament in T-15 Upgrade Tokamak

The formation in the T-15 Upgrade tokamak of plasma filaments with a smaller volume than in the base discharge scenario, keeping the total plasma current constant, has been studied by numerical simulation. The purpose of such operating regimes is to raise the specific power of additional plasma heating. These regimes are of interest for attaining highest possible temperatures under limited additional heating power, e.g., for attaining AT (Advanced Tokamak) regimes. Additionally, these operating regimes can be investigated in the early stage of the T-15 Upgrade experiments when the total available heating power is low. Calculations with the Tokameq code have produced stationary equilibrium configurations for reduced plasma volume regimes. Three variants of plasma-volume reduction have been considered: displacing the plasma filament to the strong magnetic field region near the inner chamber wall while maintaining the filament center in the equatorial plane, and also displacing the plasma filament up or down. Numerical calculations have shown that such regimes may reduce the plasma-filament volume by a factor of 2 to 5, thus significantly raising the specific power of additional heating.