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: 1.58). 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.

0 Bookmarks
 · 
133 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: Plasma created by an inductive RF discharge is allowed to expand along a diverging magnetic field. Measurement of the axial plasma potential profile reveals the formation of an electric double layer near the throat of the expansion chamber. An accelerated ion beam has been detected in the downstream region, confirming the presence of the double layer. The 2-D nature of the ion energy distribution function of the downstream plasma has been studied by a movable ion energy analyser, which shows that the beam radius increases along the axial distance. The 2-D structure of the plasma potential has been studied by a movable emissive probe. The existence of a secondary lobe in the contour plot of plasma equipotential is a new observation. It is also an interesting observation that the most diverging magnetic field line not intercepting the junction of the discharge tube and the expansion chamber has an electric field aligned with it.
    Physics of Plasmas 09/2012; 19(9). DOI:10.1063/1.4752074 · 2.25 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The ion acoustic beam-plasma instability is known to excite strong solitary waves near the Earth's bow shock. Using a double plasma experiment, tightly coupled with a 1-dimensional particle-in-cell simulation, the results presented here show that this instability is critically sensitive to the experimental conditions. Boundary effects, which do not have any counterpart in space or in most simulations, unavoidably excite parasitic instabilities. Potential fluctuations from these instabilities lead to an increase of the beam temperature which reduces the growth rate such that non-linear effects leading to solitary waves are less likely to be observed. Furthermore, the increased temperature modifies the range of beam velocities for which an ion acoustic beam plasma instability is observed.
    Physics of Plasmas 05/2014; 21(5):052103. DOI:10.1063/1.4875577 · 2.25 Impact Factor
  • 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.
    Physics of Plasmas 01/2010; 17(5). DOI:10.1063/1.3276773 · 2.25 Impact Factor

Full-text (2 Sources)

Download
13 Downloads
Available from
Jul 14, 2014