Langmuir wave self-focusing versus decay instability
- Los Alamos National Laboratory, MS-B213, Los Alamos, New Mexico 87545 (United States)
Electron trapping in a finite amplitude Langmuir wave (LW) leads to a frequency shift, {delta}{omega}{sub TP}<0, and reduced Landau damping. These may lead to modulational instability. Its growth rate and damping threshold, due to escape of trapped electrons at rate {nu}, are calculated in the short wavelength regime. If the background plasma is in thermal equilibrium, it is shown that this trapped particle modulational instability (TPMI) is not possible when k{lambda}{sub D}>0.46, while for 0.33<k{lambda}{sub D}<0.46 TPMI requires that the fluctuation wave vector has a component perpendicular to k, the LW wave vector, with {lambda}{sub D} being the electron Debye length. Its nonlinear evolution leads to self-focusing. Comparison is made with a reevaluated LW ion acoustic decay instability (LDI): compared to classical estimates, the new linear LDI threshold is lowered by primary LW {delta}{omega}{sub TP} since frequency matching leads to wave number and hence damping reduction of the daughter LW. For parameter estimates relevant to a recent stimulated Raman scatter experiment [Kline et al., Phys. Rev. Lett. (submitted)], the LDI and TPMI thresholds cross in the range 0.29<k{lambda}{sub D}<0.33, consistent with the observed LDI regime change. However, if {nu} exceeds a critical value, estimated to be order 1% of the electron plasma frequency, then TPMI is not possible at any wave number.
- OSTI ID:
- 20657961
- Journal Information:
- Physics of Plasmas, Vol. 12, Issue 1; Other Information: DOI: 10.1063/1.1829066; (c) 2005 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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