Kinetic Effects in Nonlinear Plasma Waves

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This award supports a program of experiments, simulations, and theory on a new type of instability of large amplitude plasma waves - waves in a gas of freely interacting electrically charged particles. The studies will focus on and characterize novel 'kinetic' effects that appear to dominate this instability in waves that propagate with nearly constant wave speed. Such waves are ubiquitous in both naturally-occurring and laboratory plasmas. The new instability mechanism is quite simple and general, and therefore has application to a range of scenarios, including space plasmas and fusion plasmas for power generation.Experiments will be performed on non-neutral plasmas, utilizing an electron trap and an ion trap with a broad range of operating regimes and diagnostics. The simplicity of these systems allows a depth of understanding and a precision of comparison between theory and experiment which is rarely possible for quasi-neutral plasmas in complex geometry. The goal is to verify applicability of the theory, and to stimulate new theory where needed. Recent analysis has found that, surprisingly, standard fluid theory is inadequate to describe parametric instability for near-acoustic Trivelpiece-Gould [TG] plasma waves. A new kinetic instability mechanism, involving a small fraction of plasma that is trapped in the wave troughs, will be studied and applied to understand parametric instabilities observed both in TG waves and in electron-acoustic waves. Experiments and simulations will be used to characterize the particle distribution under the action of the wave, including trapped particles, for direct comparison to theory.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.