High performance discharges and capabilities in alcator C-Mod

Abstract

Alcator C-Mod is a compact, diverted, shaped, high magnetic field (B = 9 T) tokamak operating at the Massachusetts Institute of Technology Plasma Fusion Center. The machine interior is all metallic, and the walls and divertor region are covered with molybdenum tiles. The vacuum vessel is a continuous, thick wall stainless steel construction, prototypical of future fusion devices (e.g., ITER). Typical discharge cleaning utilizes ECDC, or electron-cyclotron discharge cleaning, in the steady state at low magnetic field (0.0875 T). While its dimensions are compact (R = 0.67 m, a = 0.22 m, K = 1.8), C-Mod is designed to operate up to 2.5 MA at 9.0 T magnetic field. To present date the machine has operated at currents up to 1.5 MA at B = 5.3 T, and magnetic fields up to 8.0 T at I{sub p} = 1.2 MA. Due to the high current density, line average densities of 4.0 x 10{sup 20} m{sup {minus}3} are obtained with gas fueling, and peak densities in excess of 1.0 x 10{sup 21} m{sup {minus}3} have been obtained with pellet fueling. Typical pulse lengths are up to 2.0 seconds, with a flat-top of typically 1.0 sec. Presently the device is equipped withmore » 4.0 MW of ICRF heating power operating at 80 MHz, but this capability is being upgraded to 8.0 MW with the addition of 4.0 MW of tunable ICRF power operating at 40.80 MHz. A 20 pellet/pulse deuterium injector is operational, and a 4 pellet Li injector is also operational. To reduce the influx of metallic impurities during high power operation, recently boronization of the machine interior was begun prior to plasma discharges, this allowed plasma operation with full auxiliary power capability without excessive radiative power losses from the plasma core. 7 refs.« less