An experimental study of lower-hybrid wave driven high-poloidal beta plasmas in the Versator II tokamak
High poloidal beta plasma equilibria have been produced by both toroidally asymmetric and symmetric lower-hybrid rf injection in the Versator II tokamak. (Here [beta][sub p] is the ratio of the plasma pressure to the poloidal magnetic field pressure, and [epsilon] = a/R[sub 0] is the inverse aspect ratio). In both cases the plasma current was fully sustained by the rf, with the loop voltage negligibly small. The rf-created high energy electron distribution function, which provides a large fraction of plasma current and pressure in these plasmas, is studied by means of X-ray spectroscopy of the electron-ion perpendicular to the toroidal magnetic field and emission measurements at a full range of angles to the toroidal magnetic field have been carried out. For low plasma current equilibria, [beta][sub p] is enhanced, and an outward shift in major radius of the X-ray emission profile peak was observed, corresponding to a Shafranov shift of the magnetic axis. The LHCD equilibrium current profiles was determined from the X-ray emission profile. The LHCD X-ray data indicate a highly anisotropic energetic electron distribution function with a density approximately 1% of the bulk electron density at the center. The stored energy of this distribution is much larger than the bulk energy and the global energy confinement time scales in agreement with the Kaye-Goldston L-mode scaling. At high values of [beta][sub p] [approximately] 3, LHH generates nearly the same plasma current as LHCD. The LHH equilibria has a reduction of up to a factor of four in the high energy X-ray emission flux, as compared to LHCD. Modeling of the electron distribution function in the LHH case indicates that only one third of the current is carried by the high energy electrons. At lower values of [beta][sub p] [approximately] 1.5, LHH requires the assistance of a small applied loop voltage to maintain the plasma current and the high energy electrons carry a majority of the plasma current.
- Research Organization:
- Massachusetts Inst. of Tech., Cambridge, MA (United States)
- OSTI ID:
- 7000494
- Resource Relation:
- Other Information: Thesis (Ph.D.)
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
HIGH-BETA PLASMA
LOWER HYBRID CURRENT DRIVE
VERSATOR TOKAMAK
BOOTSTRAP CURRENT
EXPERIMENTAL DATA
CLOSED PLASMA DEVICES
CURRENTS
DATA
ELECTRIC CURRENTS
INFORMATION
NON-INDUCTIVE CURRENT DRIVE
NUMERICAL DATA
PLASMA
THERMONUCLEAR DEVICES
TOKAMAK DEVICES
700350* - Plasma Production
Heating
Current Drive
& Interactions- (1992-)