Study of parametric instabilities during the Alcator C lower hybrid wave heating experiments

Technical Report · Sat Oct 01 04:00:00 EDT 1983

OSTI ID:5575466

Takase, Y

Parametric excitation of ion-cyclotron quasi-modes (..omega../sub R/ approx. = n..omega../sub ci/) and ion-sound quasi-modes (..omega../sub R/ approx. = k/sub parallel to/v/sub ti/) during lower hybrid wave heating of tokamak plasmas have been studied in detail. Such instabilities may significantly modify the incident wavenumber spectrum near the plasma edge. Convective losses for these instabilities are high if well-defined resonance cones exist, but they are significantly reduced if the resonance cones spread and fill the plasma volume (or some region of it). These instabilities preferentially excite lower hybrid waves with larger values of n/sub parallel to/ than themselves possess, and the new waves tend to be absorbed near the outer layers of the plasma. Parametric instabilities during lower hybrid heating of Alcator C plasmas have been investigated using rf probes (to study tilde phi and tilde n/sub i/) and CO/sub 2/ scattering technique (to study tilde n/sub e/). At lower densities (anti n/sub e/ less than or equal to 0.5 x 10/sup 14/cm/sup -3/) where waves observed in the plasma interior using CO/sub 2/ scattering appear to be localized, parametric decay is very weak. Both ion-sound and ion-cyclotron parametric decay processes have been observed at higher densities (anti n greater than or equal to 1.5 x 10/sup 14/cm/sup -3/) where waves appear to be unlocalized. Finally, at still higher densities (anti n /sub e/ greater than or equal to 2 x 10/sup 4/cm/sup -3/) pump depletion has been observed. Above these densities heating and current drive efficiencies are expected to degrade significantly.

• Research Organization: Massachusetts Inst. of Tech., Cambridge (USA). Plasma Fusion Center
• DOE Contract Number: AC02-78ET51013
• OSTI ID: 5575466
• Report Number(s): DOE/ET/51013-100; ON: DE84002809
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
700107* -- Fusion Energy-- Plasma Research-- Instabilities
ALCATOR DEVICE
CARBON DIOXIDE LASERS
CLOSED PLASMA DEVICES
CONVECTIVE INSTABILITIES
CYCLOTRON FREQUENCY
ELECTROMAGNETIC RADIATION
GAS LASERS
HEATING
HIGH-FREQUENCY HEATING
INSTABILITY
ION ACOUSTIC WAVES
ION WAVES
LASER RADIATION
LASERS
LOWER HYBRID HEATING
PARAMETRIC INSTABILITIES
PLASMA HEATING
PLASMA INSTABILITY
PLASMA MACROINSTABILITIES
PLASMA WAVES
RADIATIONS
THERMONUCLEAR DEVICES
TOKAMAK DEVICES