On the role of ion temperature anisotropy in the growth and propagation of shear‐modified ion‐acoustic waves

Abstract

Oblique ion‐acoustic waves, excited by the combination of magnetic field‐aligned (parallel) electron drift and sheared parallel ion flow, are investigated in magnetized laboratory plasma that is characterized by ion temperature anisotropy. Direct measurements of the parallel and perpendicular ion temperatures, parallel and perpendicular ion drift velocities, electron temperature and parallel electron drift velocity, parallel and perpendicular wave vector components, and mode frequency and growth rate are used to elucidate the shear‐modified ion‐acoustic (SMIA) instability mechanism and document an observed correlation between ion temperature anisotropy and wave propagation angle. Experimental measurements show that anisotropy significantly influences the growth rate and propagation angle of oblique ion‐acoustic waves. These results support the ion‐acoustic wave interpretation of broadband waves in the auroral energization region where shear and anisotropy are known to exist and may have ramifications for many space plasmas in which anisotropy exists in the electron temperature or ion temperature.