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Title: Effects of neutral interactions on velocity-shear-driven plasma waves

In a laboratory experiment, we demonstrate the substantial effects that collisions between charged and neutral particles have on low-frequency (Ω{sub i} ≪ ω ≪ Ω{sub e}) 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.more » 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.« less
Authors:
 [1] ; ; ; ;  [2] ;  [3]
  1. Physics Department, US Air Force Academy, Colorado Springs, Colorado 80840 (United States)
  2. Plasma Physics Division, Naval Research Laboratory, Washington, DC 20375 (United States)
  3. Sensors Directorate, Air Force Research Laboratory, Dayton, Ohio 45433 (United States)
Publication Date:
OSTI Identifier:
22299963
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 21; Journal Issue: 6; Other Information: (c) 2014 U.S. Government; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ELECTRIC FIELDS; IONS; LOWER HYBRID CURRENT DRIVE; LOWER HYBRID HEATING; NUMERICAL SOLUTION; PLASMA DENSITY; PLASMA INSTABILITY; PLASMA WAVES; SHEAR; VELOCITY