Stabilization of sawteeth by lower hybrid waves in the Alcator C tokamak

PFC / JA - 87 - 32 Stabilization of Sawteeth By Lower Hybrid Waves in the Alcator

Sawteeth have been suppressed by lower hybrid current drive in high density Alcator C plasmas. At a density of 1.1 x 101 4 cm-3 and q(a) = 4.7 the sawteeth were eliminated by application of P,.f = 600 kW at 4.6 GHz, which represents an estimated 30% of the rf power required to fully sustain the discharge in the absence of ohmic power. Strong electron heating is observed with both current drive ...

Dissipative Divertor Operation in the Alcator C-mod Tokamak Dissipative Divertor Operation in the Alcator C-mod Tokamak

The achievement of large volumetric power losses (dissipation) in the Alcator C-Mod divertor region is demonstrated in two operational modes: radiative divertor and detached divertor. During radiative divertor operation, the fraction of SOL power lost by radiation is P R/PSOL0.8 with single null plasmas, n e < 2x10 20 m-3 and I < 1 MA. These plasmas sometimes have very high recycling, with nedi...

Modification of H-mode pedestal structure with lower hybrid waves on Alcator C Mod

The application of lower hybrid waves (LH) in H-mode plasmas on Alcator C-Mod can result in significant reduction of core particle inventory, with no significant degradation of energy confinement. This phenomenon has been observed in steady enhanced Dα (EDA) H-mode targets, which are sustained by ion cyclotron RF auxiliary heating, in which pedestal density nped is usually tied firmly to plasma...

Fully Ionized and Total Abundances in the Alcator-C Tokamak

Pfc/ja-83-37 Impurity Generation during Intense Lower Hybrid Heating Experiments on the Alcator C Tokamak

Experiments are underway on the Alcator C Tokamak with over 1 MW of RF power injected into the plasma at a frequency of 4.6 GHz to study both heating and current drive effects. During these studies, impurity generation from limiter structures has been observed. The RF induced impurity influx is a strongly nonlinear function of net injected power. For Prf < 500 kW, only small effects are seen. A...