Nonlinearly driven second harmonics of Alfven cascades
- Department of Radio and Space Science, Chalmers University of Technology, SE-412 96 Goeteborg (Sweden)
In recent experiments on Alcator C-Mod [J. A. Snipes et al., Phys. Plasmas 12, 056102 (2005)], measurements of density fluctuations with phase contrast imaging through the plasma core show a second harmonic of the basic Alfven cascade (AC) signal. The present paper presents a theory that describes the second-harmonic perturbation as a nonlinear sideband produced by the AC eigenmode via quadratic terms in the magnetohydrodynamic equations. It is shown that in a low-pressure plasma the nonlinear coupling to compressional Alfven and acoustic perturbations can be neglected when calculating the second-harmonic density. The derived expressions for this density perturbation can potentially be used together with experimental measurements to determine the AC amplitude inside the plasma, rather than just at the edge as with magnetic probes.
- OSTI ID:
- 20782740
- Journal Information:
- Physics of Plasmas, Vol. 13, Issue 4; Other Information: DOI: 10.1063/1.2192500; (c) 2006 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 1070-664X
- Country of Publication:
- United States
- Language:
- English
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Nonlinearly driven harmonics of Alfvén modes