Axisymmetric instability in a noncircular tokamak

Thesis/Dissertation · Mon Jan 01 04:00:00 EST 1979

OSTI ID:6630950

Lipschultz, B

The stability of dee, inverse-dee and square crosssection plasmas to axisymmetric modes has been investigated experimentally in Tokapole II, a tokamak with a four-null poloidal divertor. Experimental results are closely compared with predictions of two numerical stability codes - the PEST code (ideal MHD, linear stability) adapted to tokapole geometry and a code which follows the nonlinear evolution of shapes similar to tokapole equilibria. Experimentally, the square is vertically stable and both dee's unstable to a vertical nonrigid axisymmetric shift. The central magnetic axis displacement grows exponentially with a growth time /sup approx./10/sup 3/ poloidal Alfven times/sup approx./ plasma L/R time. Proper initial positioning of the plasma on the midplane allows passive feedback to nonlinearly restore vertical motion to a small stable oscillation about the center. Experimental poloidal flux plots are produced directly from internal magnetic probe measurements. The PEST code, ignoring passive feedback, predicts all equilibria to be vertically unstable with the square having the slowest growth. With passive feedback, all are stable. Thus experiment and code agree that the square is the most stable shape, but experiment indicates that passive feedback is partially defeated by finite plasma resistivity. In both code and experiment square-like equilibria exhibit a relatively harmless horizontal instability.

• Research Organization: Wisconsin Univ., Madison (USA)
• OSTI ID: 6630950
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
700107* -- Fusion Energy-- Plasma Research-- Instabilities
CLOSED PLASMA DEVICES
COMPUTER CALCULATIONS
GEOMETRY
INSTABILITY
INTERNAL RING DEVICES
MATHEMATICS
PLASMA INSTABILITY
SYMMETRY
THERMONUCLEAR DEVICES
TOKAMAK DEVICES
TOKAPOLE DEVICES