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Pure electron plasma dynamics in the CNT stellarator

Author: Thomas Pedersen
Requested Type: Poster Only
Submitted: 2006-12-15 11:07:20

Co-authors: J. Berkery, Q. Marksteiner, M. Hahn, R. G. Lefrancois, J. P. Kremer, H. Himura

Contact Info:
Columbia University
500 W 120th Street, S.W. Mudd
New York, NY   10027
United States

Abstract Text:
The Columbia Non-neutral Torus (CNT) is dedicated to the study of non-neutral plasmas confined on magnetic surfaces. CNT is a simple stellarator created from four circular coils, and has been in operation at Columbia University since Nov 2004. First results include confirmation of small Debye length, stable equilibria (Kremer, PRL, 2006) and studies of particle transport and confinement times (Berkery, this conference). We will discuss recent observations of dynamic plasma behavior in CNT. When the neutral pressure is elevated, CNT has an ion content on the order of 2-10%, and an instability appears, at low B field strengths (~0.02 T). The instability can either appear as repeated bursts or it can saturate to a constant amplitude near-sinusoidal oscillation. The frequency of the instability is in the 10-40 kHz range, which is in good agreement with the electron fluid ExB rotation rate. The orbital motion of ions is complicated - the ion Larmor radius is on the order of the minor radius of CNT for these experiments, and the ions are accelerated as they enter the core of the plasma, due to the electron space charge. However, the typical frequency of the ion motion is also in the 10-40 kHz range. This instability may be a helical analogue of the ion resonant instability seen in electron plasmas confined in Penning traps.
Other experiments performed at high electron density and low B-field show sudden confinement jumps at particular bias voltages of the electron emitter. These observations will be shown and discussed. We will also discuss other ongoing and planned research, including plasma profile studies, electron-positron plasma experiments, and our proposed plan to study magnetic reconnection in neutral plasmas in CNT.

Characterization: A5,E10


University of Maryland

Innovative Confinement Concepts Workshop
February 12-14, 2007
College Park, Maryland

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