Nonlinear Amplification and Decay of Phase-mixed Waves in Compressing Plasma
Authors: Paul F. Schmit, I.Y. Dodin, J. Rocks, and N.J. Fisch
Abstract:
Through particle-in-cell simulations, we show that plasma waves carrying trapped electrons can be
amplified manyfold via compressing plasma perpendicularly to the wave vector. These simulations
are the first ab initio demonstration of the conservation of nonlinear action for such waves, which
contains a term independent of the field amplitude. In agreement with the theory, the maximum of
amplification gain is determined by the total initial energy of the trapped-particle average motion
but otherwise is insensitive to the particle distribution. Further compression destroys the wave;
electrons are then untrapped at suprathermal energies and form a residual beam. As compression
continues, the bump-on-tail instability is triggered each time one of the discrete modes comes in
resonance with this beam. Hence, periodic bursts of the electrostatic energy are produced until a
wide quasilinear plateau is formed.
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Submitted to: Physical Review Letters (September, 2012)
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Download PPPL-4817 (pdf KB pp)
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