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Title: Spatial profiles of electron and metastable atom densities in positive polarity fast ionization waves sustained in helium

Fast ionization waves (FIWs), often generated with high voltage pulses over nanosecond timescales, are able to produce large volumes of ions and excited states at moderate pressures. The mechanisms of FIW propagation were experimentally and computationally investigated to provide insights into the manner in which these large volumes are excited. The two-dimensional structure of electron and metastable densities produced by short-pulse FIWs sustained in helium were measured using laser-induced fluorescence and laser collision-induced fluorescence diagnostics for times of 100–120 ns after the pulse, as the pressure was varied from 1 to 20 Torr. A trend of center-peaked to volume-filling to wall-peaked electron density profiles was observed as the pressure was increased. Instantaneous FIW velocities, obtained from plasma-induced emission, ranged from 0.1 to 3×10⁹cm s⁻¹, depending on distance from the high voltage electrode and pressure. Predictions from two-dimensional modeling of the propagation of a single FIW correlated well with the experimental trends in electron density profiles and wave velocity. Results from the model show that the maximum ionization rate occurs in the wavefront, and the discharge continues to propagate forward after the removal of high voltage from the powered electrode due to the potential energy stored in the space charge. Asmore » the pressure is varied, the radial distribution of the ionization rate is shaped by changes in the electron mean free path, and subsequent localized electric field enhancement at the walls or on the centerline of the discharge.« less
Authors:
;  [1] ; ;  [2]
  1. Sandia National Laboratories, Albuquerque, New Mexico 87185-1423 (United States)
  2. Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan 48109-2122, USA. (United States)
Publication Date:
OSTI Identifier:
22305931
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 116; Journal Issue: 10; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ATOMS; DENSITY; ELECTRIC FIELDS; ELECTRIC POTENTIAL; ELECTRODES; ELECTRON DENSITY; ELECTRONS; EXCITED STATES; FLUORESCENCE; FORECASTING; HELIUM; IONIZATION; LASER RADIATION; MEAN FREE PATH; PLASMA; POTENTIAL ENERGY; SIMULATION; SPACE CHARGE; SPATIAL DISTRIBUTION; TWO-DIMENSIONAL CALCULATIONS