Abstract Details

Low Frequency Instability in the Levitated Dipole Experiment

Author: Jay Kesner
Submitted: 2005-12-21 16:41:19

Co-authors: A. Boxer, J. Ellsworth, D.T. Garnier, A.K. Hansen, I. Karim, M.E. Mauel, E.E. Ortiz

Contact Info:
MIT PSFC
77 Mass Ave
Cambridge, Ma   02139
USA

Abstract Text:
Plasma that is heated by ECRH can be subject to instability that feeds on the free energy of either the hot component or the thermal plasma component. Confinement a closed field line system such as a levitated dipole imposes particular restrictions on collective effects; notably the plasma compressibility will play an important stabilizing role. Theoretical considerations of thermal plasma driven instability indicate the possibility of MHD-like behavior of the background plasma, including convective cells, drift frequency (entropy mode) fluctuations and ECRH-accessibility related "breather" modes. In experiments in LDX (in the supported mode of operation) we create a 2 component plasma in which a thermal species contains most of the density and an energetic electron species contains most of the plasma stored energy. In addition to high frequency fluctuations reported elsewhere [Garnier et al, submitted to PRL (2005)] we observe low frequency fluctuations that presumably relate to the thermal species. The observed frequencies include modes in the kHz and 100 Hz range. A variation of the frequency spectrum with heating profile and a temporal variation as the plasma approached a steady state indicates a dependence on the imposed plasma profiles and possibly on the relative temperature and density gradients. Both theoretical considerations and experimental observations will be discussed.

Characterization: A2,A5

Comments:
Please group LDX abstracts together in the order Mauel et al, Kesner et al, Garnier et al, Hansen et al.