Journal article
Laser-induced fluorescence measurements of ion fluctuations in electron and ion presheaths
Physics of plasmas, Vol.27(5), p.53509
05/01/2020
DOI: 10.1063/1.5142014
Abstract
Electrostatic flow-driven instabilities have been predicted in the presheath region of low-temperature plasmas for both ion and electron rich sheaths. The ion-acoustic fluctuations that arise from these instabilities can influence transport through an enhanced collision rate. In this work, ion fluctuation spectra were measured using laser-induced fluorescence (LIF) in the presheath region for both sheath polarities. The non-invasive nature of LIF compared to that of probes is particularly valuable for these measurements because the sheath and presheath around a probe may generate their own flow-driven instabilities, which obscure the measurement. Measurements were made using a recently implemented field programmable gate array-based system able to measure ion fluctuation spectra up to 1MHz using a two-point correlation function technique. Narrow bandwidth ion fluctuations were observed near 0.46f(pi) (460kHz) for both sheath polarities, where f(pi) is the ion plasma frequency. The observed fluctuations were significantly stronger in the electron sheath case and were observed over a larger volume of plasma. Fluctuations were measured in the ion sheath case at locations far enough from the sheath that linear theory predicts stability, suggesting that ion-acoustic instabilities generated in the relatively small unstable region near the boundary reflect from the sheath and perturb a much larger volume of the plasma. This is expected to affect probes with both ion and electron rich sheaths, meaning any dc biased probe may effectively act as an ion-acoustic wave antenna. These measurements are consistent with the recent theory and particle-in-cell results. Published under license by AIP Publishing.
Details
- Title: Subtitle
- Laser-induced fluorescence measurements of ion fluctuations in electron and ion presheaths
- Creators
- R. Hood - University of IowaS. D. Baalrud - University of IowaR. L. Merlino - University of IowaF. Skiff - University of Iowa
- Resource Type
- Journal article
- Publication Details
- Physics of plasmas, Vol.27(5), p.53509
- Publisher
- AIP Publishing
- DOI
- 10.1063/1.5142014
- ISSN
- 1070-664X
- eISSN
- 1089-7674
- Number of pages
- 8
- Grant note
- DE-SC0016473 / Office of Fusion Energy Sciences at the U.S. Department of Energy
- Language
- English
- Date published
- 05/01/2020
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9984428670202771
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