Effects of neutral interactions on velocity-shear-driven plasma waves
Abstract
In a laboratory experiment, we demonstrate the substantial effects that collisions between charged and neutral particles have on low-frequency (Ωi ≪ ω ≪ Ωe) shear-driven electrostatic lower hybrid waves in a plasma. We establish a strong (up to 2.5 kV/m) highly localized electric field with a length scale shorter than the ion gyroradius, so that the ions in the plasma, unlike the electrons, do not develop the full E × B drift velocity. The resulting shear in the particle velocities initiates the electron-ion hybrid (EIH) instability, and we observe the formation of strong waves in the vicinity of the shear with variations in plasma densities of 10% or greater. Our experimental configuration allows us to vary the neutral background density by more than a factor of two while holding the charged particle density effectively constant. Not surprisingly, increasing the neutral density decreases the growth rate/saturation amplitude of the waves and increases the threshold electric field necessary for wave formation, but the presence of neutrals affects the dominant wave frequency as well. We show that a 50% increase in the neutral density decreases the wave frequency by 20% while also suppressing the electric field dependence of the frequency that is observed when fewer neutrals are present. The majority of these effects, as well as the values of the frequencies we observe, closely match the predictions of previously developed linear EIH instability theory, for which we present the results of a numerical solution.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Jun 01, 2014
- Source ID
- 10.1063/1.4885315
Entities
People
- C L Enloe
- C. Crabtree
- E. M. Tejero
- G. Ganguli
- V. I. Sotnikov
- W. E. Amatucci
Organizations
- Air Force Office of Scientific Research
- Air Force Research Laboratory
- United States Air Force Academy
- United States Naval Research Laboratory