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The Levitated Dipole Experiment: Experiment and Theory

Author: Jay Kesner
Requested Type: Poster Only
Submitted: 2009-12-04 14:33:57

Co-authors: M. DAVIS, J. ELLSWORTH, D.T. GARNIER, B. KARDON, M. MAUEL, P. MICHAEL, P. WOSKOV

Contact Info:
MIT PSFC
175 Albany St NW17-213
Cambridge, Ma   02446
USA

Abstract Text:
A closed field line confinement system such as a levitated dipole is shear-free and the plasma compressibility provides stability. Theoretical considerations indicate the possibility of both MHD and electrostatic instability that can create turbulent driven transport. Importantly, the resulting transport is expected to create ``stationary", inwardly-peaked density and pressure profiles. The particle and energy confinement times in a dipole can be simply understood in terms of the stationary profiles and the energy confinement time can substantially exceed the particle time. The implications for a power source will be discussed.

In LDX, ECH is used to create a low density hot-electron species embedded in a background plasma which, during levitation, is seen to contain approximately half of the stored energy. When the floating coil is levitated, competing along-the-field-line losses are not present (all losses become cross-field) and near-stationary density profiles are observed. For edge fueling this inwardly peaked density requires an inward pinch which is also observed. Low frequency (kHz range) fluctuations appear that presumably maintain these profiles and the pinch time is consistent with a measured diffusion coefficient. The plasma edge is turbulent and for stationary profiles the edge parameters provide boundary conditions which determine the core parameters.

Characterization: A2,A5

Comments:
1) Kesner, 2) Davis, 3) Woskov, 4) Worstell, 5) Senter