Article

Comparison of gridded energy analyzer and laser induced fluorescence measurements of a two-component ion distribution

Department of Physics, West Virginia University, Morgantown, West Virginia 26506-6315, USA.
The Review of scientific instruments (Impact Factor: 1.61). 11/2008; 79(10):10F314. DOI: 10.1063/1.2953411
Source: PubMed

ABSTRACT

We present ion velocity distribution function (IVDF) measurements obtained with a five grid retarding field energy analyzer (RFEA) and IVDF measurements obtained with laser induced fluorescence (LIF) for an expanding helicon plasma. The ion population consists of a background population and an energetic ion beam. When the RFEA measurements are corrected for acceleration due to the electric potential difference across the plasma sheath, we find that the RFEA measurements indicate a smaller background to beam density ratio and a much larger parallel ion temperature than the LIF. The energy of the ion beam is the same in both measurements. These results suggest that ion heating occurs during the transit of the background ions through the sheath and that LIF cannot detect the fraction of the ion beam whose metastable population has been eliminated by collisions.

Download full-text

Full-text

Available from: Alex Hansen, Jul 14, 2014
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We report observations that confirm a theoretical prediction that formation of a current-free double layer in a plasma expanding into a chamber of larger diameter is accompanied by an increase in ionization upstream of the double layer. The theoretical model argues that the increased ionization is needed to balance the difference in diffusive losses upstream and downstream of the expansion region. In our expanding helicon source experiments, we find that the upstream plasma density increases sharply at the same antenna frequency at which the double layer appears.
    Full-text · Article · Feb 2009 · Physical Review Letters
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Observations in steady-state plasmas confirm predictions that formation of a current-free double layer in a plasma expanding into a chamber of larger diameter is accompanied by an increase in ionization upstream of the double layer. The upstream plasma density increases sharply at the same driving frequency at which a double layer appears. For driving frequencies at which no double layer appears, large electrostatic instabilities are observed. Time-resolved measurements in pulsed discharges indicate that the double layer initially forms for all driving frequencies. However, for particularly strong double layers, instabilities appear early in the discharge and the double layer collapses.
    Full-text · Article · Jan 2010 · Physics of Plasmas
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We report detailed studies of a threshold antenna frequency for the creation of an ion beam due to the formation of a stable electric double layer (DL) in an expanding, low pressure, argon helicon plasma. Mutually consistent measurements of ion beam energy and density obtained with a retarding field energy analyzer and laser-induced-fluorescence indicate that a stable ion beam of approximately 15 eV appears for antenna frequencies above 11.5 MHz. At lower antenna frequencies, for which the rf coupling to the plasma improves, large electrostatic instabilities appear downstream of the expansion region and a well-formed ion beam is not observed. Further studies of the low frequency (~17.5 kHz) electrostatic fluctuations suggest that they arise from beam-driven, ion acoustic instabilities. We also observe a sharp increase in the upstream density at the same threshold antenna frequency, confirming a theoretical model that predicts an increase in the upstream density due to enhanced ionization resulting from electrons accelerated upstream by the DL.
    Full-text · Article · Feb 2010 · Plasma Sources Science and Technology
Show more