Control of gradient-driven instabilities using shear Alfvén beat waves

Abstract

A new technique for manipulation and control of gradient-driven instabilities through nonlinear interaction with Alfvén waves in a laboratory plasma is presented. A narrow field-aligned density depletion is created in the Large Plasma Device (LAPD), resulting in coherent unstable fluctuations on the periphery of the depletion. Two independent kinetic Alfvén waves are launched along the depletion at separate frequencies, creating a nonlinear beat-wave response at or near the frequency of the original instability. When the beat-wave has sufficient amplitude, the original unstable mode is suppressed, leaving only the beat-wave response at a different frequency, generally at lower amplitude.

Submitted for Publication in Physical Review Letters. Revision 2 reflects changes suggested by referees for PRL submission. One figure removed, several major changes to another figure, and a number of major and minor changes to the text