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Thermal Fluctuations: Modes versus the Continuum

Gould, Roy W. (2003) Thermal Fluctuations: Modes versus the Continuum. In: Non-Neutral Plasma Physics V. American Institute of Physics Conference Proceedings. No.692. American Institute of Physics , pp. 15-21. ISBN 073540165 http://resolver.caltech.edu/CaltechAUTHORS:GOUaipcp03

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Abstract

The thermal fluctuation spectrum of the signal received on a patch electrode is examined and it is shown that the spectrum shows both the modes of the plasma and a continuous spectrum related to the independent-particle motions of plasma electrons. Modes whose axial phase velocity are more than 3–4 times the electron thermal speed are lightly Landau-damped and are clearly separated from the continuum. Long wavelength modes are "acoustic" in nature. If the axial phase velocity of a mode becomes less than 1–2 times the electron thermal speed, then the mode becomes strongly Landau-damped and it merges into the continuum. The mode velocities are of the order of wpa , where a is the plasma radius, so that the plasma radius must be at least several deBye lengths in order to have lightly damped modes. In general, the spectrum is a mixture of a continuous spectrum together with a finite number of modes which are Landau-damped by varying amounts, depending on their phase velocity relative to the electron thermal speed. Only in the extreme limit, wpa << vth does the continuous spectrum tend to a Gaussian of width k vth, characteristic of independent particles. The effect of the "load impedance" on the measurements is also discussed.


Item Type:Book Section
Additional Information:©2003 American Institute of Physics The author is grateful to N. Shiga, F. Anderegg, and other members of the U.C.S.D. group for stimulating discussions of their results.
Subject Keywords:electrons; plasma fluctuations; spectral analysis; vibrational modes; velocity; magnetic fields; axial symmetry
Record Number:CaltechAUTHORS:GOUaipcp03
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:GOUaipcp03
Alternative URL:http://dx.doi.org/10.1063/1.1635152
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:1810
Collection:CaltechAUTHORS
Deposited By: Archive Administrator
Deposited On:19 Feb 2006
Last Modified:26 Dec 2012 08:46

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