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Volume 20, Issue 3, March 2013
In the past, long-time evolution of an initial perturbation in collisionless Maxwellian plasma (q = 1) has been simulated numerically. The controversy over the nonlinear fate of such electrostatic perturbations was resolved by Manfredi [Phys. Rev. Lett. 79, 2815–2818 (1997)] using long-time simulations up to . The oscillations were found to continue indefinitely leading to Bernstein-Greene-Kruskal (BGK)-like phase-space vortices (from here on referred as “BGK structures”). Using a newly developed, high resolution 1D Vlasov-Poisson solver based on piecewise-parabolic method (PPM) advection scheme, we investigate the nonlinear Landau damping in 1D plasma described by toy q-distributions for long times, up to . We show that BGK structures are found only for a certain range of q-values around q = 1. Beyond this window, for the generic parameters, no BGK structures were observed. We observe that for values of where velocity distributions have long tails, strong Landau damping inhibits the formation of BGK structures. On the other hand, for where distribution has a sharp fall in velocity, the formation of BGK structures is rendered difficult due to high wave number damping imposed by the steep velocity profile, which had not been previously reported. Wherever relevant, we compare our results with past work.
20(2013); http://dx.doi.org/10.1063/1.4798397View Description Hide Description
Internal fluctuations arising from energetic-particle-driven instabilities, including both density and radial magnetic field, are measured in a reversed-field-pinch plasma. The fluctuations peak near the core where fast ions reside and shift outward along the major radius as the instability transits from the n = 5 to n = 4 mode. During this transition, strong nonlinear three-wave interaction among multiple modes accompanied by enhanced fast-ion transport is observed.