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Title: A Lagrangian model for laser-induced fluorescence and its application to measurements of plasma ion temperature and electrostatic waves

Abstract

Extensive information can be obtained on wave-particle interactions and wave fields by a direct measurement of perturbed ion distribution functions using laser-induced fluorescence (LIF). For practical purposes, LIF is frequently performed on metastable states that are produced from neutral gas particles and ions in other electronic states. If the laser intensity is increased to obtain a better LIF signal, then optical pumping can produce systematic effects depending on the collision rates which control metastable population and lifetime. We numerically simulate the ion velocity distribution measurement and wave-detection process using a Lagrangian model for the LIF signal for the case where metastables are produced directly from neutrals. This case requires more strict precautions and is important for discharges with energetic primary electrons and a high density of neutrals. Some of the results also apply to metastables produced from pre-existing ions. The simulations show that optical pumping broadening affects the ion velocity distribution function f 0(v) and its first-order perturbation f 1(v,t) when the laser intensity is increased above a certain level. The results also suggest that ion temperature measurements are only accurate when the metastable ions can live longer than the ion-ion collision mean free time. For the purposes of wavemore » detection, the wave period has to be significantly shorter than the lifetime of metastable ions for a direct interpretation. It is more generally true that metastable ions may be viewed as test-particles. Finally, as long as an appropriate model is available, LIF can be extended to a range of environments.« less

Authors:
ORCiD logo [1];  [1]
  1. Univ. of Iowa, Iowa City, IA (United States). Dept. of Physics and Astronomy
Publication Date:
Research Org.:
Univ. of Iowa, Iowa City, IA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1515034
Alternate Identifier(s):
OSTI ID: 1416463
Grant/Contract Number:  
FG02-99ER54543
Resource Type:
Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 25; Journal Issue: 1; Journal ID: ISSN 1070-664X
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY

Citation Formats

Chu, Feng, and Skiff, F. A Lagrangian model for laser-induced fluorescence and its application to measurements of plasma ion temperature and electrostatic waves. United States: N. p., 2018. Web. doi:10.1063/1.5020088.
Chu, Feng, & Skiff, F. A Lagrangian model for laser-induced fluorescence and its application to measurements of plasma ion temperature and electrostatic waves. United States. doi:10.1063/1.5020088.
Chu, Feng, and Skiff, F. Wed . "A Lagrangian model for laser-induced fluorescence and its application to measurements of plasma ion temperature and electrostatic waves". United States. doi:10.1063/1.5020088. https://www.osti.gov/servlets/purl/1515034.
@article{osti_1515034,
title = {A Lagrangian model for laser-induced fluorescence and its application to measurements of plasma ion temperature and electrostatic waves},
author = {Chu, Feng and Skiff, F.},
abstractNote = {Extensive information can be obtained on wave-particle interactions and wave fields by a direct measurement of perturbed ion distribution functions using laser-induced fluorescence (LIF). For practical purposes, LIF is frequently performed on metastable states that are produced from neutral gas particles and ions in other electronic states. If the laser intensity is increased to obtain a better LIF signal, then optical pumping can produce systematic effects depending on the collision rates which control metastable population and lifetime. We numerically simulate the ion velocity distribution measurement and wave-detection process using a Lagrangian model for the LIF signal for the case where metastables are produced directly from neutrals. This case requires more strict precautions and is important for discharges with energetic primary electrons and a high density of neutrals. Some of the results also apply to metastables produced from pre-existing ions. The simulations show that optical pumping broadening affects the ion velocity distribution function f0(v) and its first-order perturbation f1(v,t) when the laser intensity is increased above a certain level. The results also suggest that ion temperature measurements are only accurate when the metastable ions can live longer than the ion-ion collision mean free time. For the purposes of wave detection, the wave period has to be significantly shorter than the lifetime of metastable ions for a direct interpretation. It is more generally true that metastable ions may be viewed as test-particles. Finally, as long as an appropriate model is available, LIF can be extended to a range of environments.},
doi = {10.1063/1.5020088},
journal = {Physics of Plasmas},
number = 1,
volume = 25,
place = {United States},
year = {2018},
month = {1}
}

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