|icc06_v3_jk.pdf||2006-03-08 13:45:12||Jay Kesner|
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
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Cambridge, Ma 02139
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.
Please group LDX abstracts together in the order Mauel et al, Kesner et al, Garnier et al, Hansen et al.