High-beta plasma effects in a low-pressure helicon plasma
Date
2007
Authors
Corr, C. S.
Boswell, R. W.
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Publisher
American Institute of Physics (AIP)
Abstract
In this work, high-beta plasma effects are investigated in a low-pressure helicon plasma source
attached to a large volume diffusion chamber. When operating above an input power of 900 W and
a magnetic field of 30 G a narrow column of bright blue light due to Ar II radiation is observed
along the axis of the diffusion chamber. With this blue mode, the plasma density is axially very
uniform in the diffusion chamber; however, the radial profiles are not, suggesting that a large
diamagnetic current might be induced. The diamagnetic behavior of the plasma has been
investigated by measuring the temporal evolution of the magnetic field Bz and the plasma kinetic
pressure when operating in a pulsed discharge mode. It is found that although the electron pressure
can exceed the magnetic field pressure by a factor of 2, a complete expulsion of the magnetic field
from the plasma interior is not observed. In fact, under our operating conditions with magnetized
ions, the maximum diamagnetism observed is 2%. It is observed that the magnetic field displays
the strongest change at the plasma centre, which corresponds to the maximum in the plasma kinetic
pressure. These results suggest that the magnetic field diffuses into the plasma sufficiently quickly
that on a long time scale only a slight perturbation of the magnetic field is ever observed.
Description
Keywords
high-beta plasma, low-pressure helicon plasma source, large volume diffusion chamber, input power of 900 W, magnetic field of 30 G, Ar II radiation, blue light
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Physics of Plasmas
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Journal article
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