Study of the fast electron distribution function in lower hybrid and electron cyclotron current driven plasmas in the WT-3 tokamak
- 1 June 1991
- journal article
- Published by IOP Publishing in Nuclear Fusion
- Vol. 31 (6) , 1015-1033
- https://doi.org/10.1088/0029-5515/31/6/002
Abstract
The distribution function f() of fast electrons produced by lower hybrid current drive (LHCD) is investigated in the WT-3 tokamak, using a combination of measurements of the hard X-ray (HXR) angular distribution with respect to the toroidal magnetic field and observations of the HXR radial profile. The data obtained indicate the formation of a plateau-like region in f() which corresponds to a region of resonant interaction between the lower hybrid (LH) wave and the electrons. The energy of the fast electrons in the peripheral plasma region is observed to be higher than that in the central plasma region under operational conditions with a high plasma current (Ip ≥ 80 kA). At low current (Ip 50 kA), however, the energy of fast electrons is constant along the plasma radius. In the current ramp-up phase, fast electrons are generated in the directions normal to and opposite to the LH wave propagation. The latter case is ascribed to a negatively biased toroidal electric field induced by the current ramp-up. To study the characteristic change of f() for various current drive mechanisms, HXR measurements are performed in electron cyclotron current driven (ECCD) plasma and in Ohmic heating (OH) plasma. In ECCD plasma, the perpendicular energy of fast electrons increases, which indicates that fast electrons are accelerated perpendicularly by electron cyclotron heating. In both LHCD and ECCD plasmas, fast electrons flow in the direction opposite to the wave propagation, while no such fast electrons are formed in OH plasma.Keywords
This publication has 33 references indexed in Scilit:
- Toroidal plasma current startup and sustainment by lower hybrid waves in the WT-3 tokamakNuclear Fusion, 1990
- Lower hybrid experiments on PLT using grills with various n∥spectral widthsNuclear Fusion, 1988
- The efficiency of RF current drive in the presence of fast particle lossesNuclear Fusion, 1987
- Cyclic tokamak operation in the WT-2 deviceNuclear Fusion, 1987
- Energy confinement studies of lower hybrid current driven plasmas in the Alcator C tokamakNuclear Fusion, 1987
- High energy X-ray measurements during lower hybrid current drive on the Alcator C tokamakNuclear Fusion, 1986
- Startup and Quasistationary Drive of Plasma Current by Lower Hybrid Waves in a TokamakPhysical Review Letters, 1984
- Formation of a 100-kA Tokamak Discharge in the Princeton Large Torus by Lower Hybrid WavesPhysical Review Letters, 1984
- Toroidal Plasma Current Startup and Sustainment by rf in the WT-2 TokamakPhysical Review Letters, 1983
- Toroidal Plasma Current Sustainment by Lower Hybrid Waves in the WT-2 TokamakPhysical Review Letters, 1981