Lower-hybrid current-drive experiments on the Alcator C and the Versator II tokamaks

Conference · Fri Apr 01 04:00:00 EST 1983

OSTI ID:5956928

Lloyd, B; Porkolab, M; Schuss, J J

On the Alcator C tokamak, lower-hybrid current-drive experiments are being carried out using two sixteen-waveguide array couplers. With the first antenna up to 650 kW of RF power has been injected at 4.6 GHz into the plasma for time durations up to 200 ms. The plasma current can be maintained at a constant level of 160 kA with zero loop voltage at a maximum electron density of anti n/sub e/ = 5.5 x 10/sup 13/ cm/sup -3/ by injecting 600 kW of RF power into the plasma. The RF current drive is strongly dependent on the phasing of adjacent waveguides, with maximum current drive efficiency obtained at ..delta..phi approx. = 60/sup 0/ to 90/sup 0/. The flat-top current drive efficiency obtained in these experiments was eta = R(m) anti n/sub e/(10/sup 14/ cm/sup -3/)I(MA)/P(MW) approx. = 0.12 at B = 10 T and eta approx. = 0.08 at B = 8 T. Current ramping was also observed. Using two sixteen-waveguide arrays, up to 1 MW of RF power was injected and RF driven currents have been produced up to a density of anti n/sub e/ approx. = 1 x 10/sup 14/ cm/sup -3/. However, for anti n/sub e/ > 7 x 10/sup 13/ cm/sup -3/, RF injection has maintained the plasma current constant for only 30 to 40 ms, at which time the molybdenum radiation level increases significantly in the presence of the high RF power. At anti n/sub e/ = 3.5 x 10/sup 13/ cm/sup -3/ and B/sub T/ = 8T in hydrogen discharges, constant plasma currents of 125 kA have been maintained by 600 kW ofRF power for more than 300 ms. During such shots the loop voltage was zero and (..beta../sub theta/ + l/sub i//2) was constant. Measurements of the hard x-ray spectrum at a density of anti n/sub e/ approx. = 5 x 10/sup 13/ cm/sup -3/ indicated an RF produced energetic tail component with photon energies up to 300 keV. In the absence of the RF power, there is no measurable level of x-ray emission above 30 keV.

• Research Organization: Massachusetts Inst. of Tech., Cambridge (USA). Plasma Fusion Center
• DOE Contract Number: AC02-78ET51013
• OSTI ID: 5956928
• Report Number(s): DOE/ET/51013-79; PFC/CP-83-8; CONF-830452-3; ON: DE83013852
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
700101* -- Fusion Energy-- Plasma Research-- Confinement
Heating
& Production
ALCATOR DEVICE
ANTENNAS
CLOSED PLASMA DEVICES
CURRENT-DRIVE HEATING
ELECTRIC HEATING
ELECTRICAL EQUIPMENT
EQUIPMENT
HEATING
HIGH-FREQUENCY HEATING
JOULE HEATING
LOWER HYBRID HEATING
PLASMA HEATING
RESISTANCE HEATING
SPECTRA
THERMONUCLEAR DEVICES
TOKAMAK DEVICES
X-RAY SPECTRA