Determination of the electron velocity distribution from the soft and hard x-ray emission during lower-hybrid current drive on PLT
During lower-hybrid heating in low-density-tokamak discharges, a nonMaxwellian tail of high-energy electrons is formed. This tail carries the plasma current. Utilizing the fact that relativistic electrons emit bremsstrahlung predominantly in the forward direction, we investigate the shape of the electron distribution by measuring the dependence of the x-ray emission on the angle between the magnetic field and the line of sight. The experimental data indicate that the distribution function is predominantly peaked in the forward direction, although a small fraction of the electrons is in the backward cone. The energy dependence of the x-ray spectra is consistent with that of a velocity distribution which has a plateau extending out to several hundred kiloelectron volts. Radial profiles show that the hot electrons are located in the central plasma region and form a high-conductivity plasma with the current profile frozen in. The slope of the spectrum depends on the rf power and on the phasing of the waveguide grill, but not on the externally applied plasma voltage. Relaxation oscillations occur shortly after switching the rf off. They also appear during the rf for low rf power and at the high-density limit of the lower-hybrid current drive. The x-ray spectra confirm that parallel energy is transferred to perpendicular energy during the instability, suggesting an instability due to the anomalous Doppler effect.
- Research Organization:
- Princeton Univ., NJ (USA). Plasma Physics Lab.
- DOE Contract Number:
- AC02-76CH03073
- OSTI ID:
- 6087405
- Report Number(s):
- PPPL-2012; CONF-830210-19; ON: DE83013720
- Resource Relation:
- Conference: 5. topical conference on radio frequency plasma heating, Madison, WI, USA, 21 Feb 1983
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
PLT DEVICES
CURRENT-DRIVE HEATING
LOWER HYBRID HEATING
X-RAY SPECTRA
DISTRIBUTION FUNCTIONS
ELECTRON DENSITY
SOFT X RADIATION
ELECTRIC HEATING
ELECTROMAGNETIC RADIATION
FUNCTIONS
HEATING
HIGH-FREQUENCY HEATING
IONIZING RADIATIONS
JOULE HEATING
PLASMA HEATING
RADIATIONS
RESISTANCE HEATING
SPECTRA
THERMONUCLEAR REACTORS
TOKAMAK TYPE REACTORS
X RADIATION
700104* - Fusion Energy- Plasma Research- Plasma Kinetics-Experimental- (-1987)