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Title: Excitation by fast atoms at very high electric field to gas-density ratios in argon

Abstract

Measurements of transient and steady-state light emission and of current transients from Ar at very high electric field to gas-density ratios {ital E}/{ital n} and low gas densities show that the excitation of the 811-nm lines of Ar is primarily by fast neutral Ar atoms. A drift tube with parallel-plane electrodes produces a spatially uniform electric field. Pulsed laser irradiation at 266 nm of the semitransparent cathode produces current pulses of {approx}10 mA and {approx}10 ns width. The time and spatial dependences of the line emission at 811{plus minus}1 and 750{plus minus}1 nm were measured for {ital E}/{ital n} in the range 280 townsend (Td) to 84 kTd at gas densities from 1.3{times}10{sup 23} to 9{times}10{sup 20} m{sup {minus}3}, where 1 Td=10{sup {minus}21} V m{sup 2}. At {ital E}/{ital n}{lt}4 kTd the time dependence of the 811-nm emission is consistent with direct and cascade excitation due to electron collisions with Ar. At {ital E}/{ital n}{gt}18 kTd the emission transient consists of an early peak caused by the initial electron avalanche followed by a delayed peak that moves toward the cathode with an apparent velocity of about twice that of the ions. Steady-state 811-nm emission is also observed in a regionmore » of very low electric field near the cathode where the Ar{sup +} ions have insufficient energy for excitation and the fast atoms are injected from a high-field region. These observations of 811-nm emission, plus previous measurements of steady-state spatial distributions of emission, are interpreted as demonstrating that excitation of the 811-nm lines is primarily by fast Ar atoms formed by charge transfer in Ar{sup +-}Ar collisions. For 750-nm emission the prompt portion is much larger and the delayed portion is much weaker than for 811-nm emission showing the importance of excitation by electrons even at these high {ital E}/{ital n} values.« less

Authors:
;  [1]
  1. Joint Institute for Laboratory Astrophysics, University of Colorado National Institute of Standards and Technology, Boulder, Colorado 80309 (US)
Publication Date:
OSTI Identifier:
5622155
Resource Type:
Journal Article
Journal Name:
Physical Review, A; (USA)
Additional Journal Information:
Journal Volume: 43:6; Journal ID: ISSN 1050-2947
Country of Publication:
United States
Language:
English
Subject:
74 ATOMIC AND MOLECULAR PHYSICS; ARGON; ATOM-ATOM COLLISIONS; DRIFT TUBES; ELECTRIC FIELDS; EMISSION SPECTRA; EXCITATION; ATOM COLLISIONS; COLLISIONS; ELEMENTS; ENERGY-LEVEL TRANSITIONS; FLUIDS; GASES; NONMETALS; RARE GASES; SPECTRA; 640304* - Atomic, Molecular & Chemical Physics- Collision Phenomena

Citation Formats

Scott, D A, and Phelps, A V. Excitation by fast atoms at very high electric field to gas-density ratios in argon. United States: N. p., 1991. Web. doi:10.1103/PhysRevA.43.3043.
Scott, D A, & Phelps, A V. Excitation by fast atoms at very high electric field to gas-density ratios in argon. United States. https://doi.org/10.1103/PhysRevA.43.3043
Scott, D A, and Phelps, A V. 1991. "Excitation by fast atoms at very high electric field to gas-density ratios in argon". United States. https://doi.org/10.1103/PhysRevA.43.3043.
@article{osti_5622155,
title = {Excitation by fast atoms at very high electric field to gas-density ratios in argon},
author = {Scott, D A and Phelps, A V},
abstractNote = {Measurements of transient and steady-state light emission and of current transients from Ar at very high electric field to gas-density ratios {ital E}/{ital n} and low gas densities show that the excitation of the 811-nm lines of Ar is primarily by fast neutral Ar atoms. A drift tube with parallel-plane electrodes produces a spatially uniform electric field. Pulsed laser irradiation at 266 nm of the semitransparent cathode produces current pulses of {approx}10 mA and {approx}10 ns width. The time and spatial dependences of the line emission at 811{plus minus}1 and 750{plus minus}1 nm were measured for {ital E}/{ital n} in the range 280 townsend (Td) to 84 kTd at gas densities from 1.3{times}10{sup 23} to 9{times}10{sup 20} m{sup {minus}3}, where 1 Td=10{sup {minus}21} V m{sup 2}. At {ital E}/{ital n}{lt}4 kTd the time dependence of the 811-nm emission is consistent with direct and cascade excitation due to electron collisions with Ar. At {ital E}/{ital n}{gt}18 kTd the emission transient consists of an early peak caused by the initial electron avalanche followed by a delayed peak that moves toward the cathode with an apparent velocity of about twice that of the ions. Steady-state 811-nm emission is also observed in a region of very low electric field near the cathode where the Ar{sup +} ions have insufficient energy for excitation and the fast atoms are injected from a high-field region. These observations of 811-nm emission, plus previous measurements of steady-state spatial distributions of emission, are interpreted as demonstrating that excitation of the 811-nm lines is primarily by fast Ar atoms formed by charge transfer in Ar{sup +-}Ar collisions. For 750-nm emission the prompt portion is much larger and the delayed portion is much weaker than for 811-nm emission showing the importance of excitation by electrons even at these high {ital E}/{ital n} values.},
doi = {10.1103/PhysRevA.43.3043},
url = {https://www.osti.gov/biblio/5622155}, journal = {Physical Review, A; (USA)},
issn = {1050-2947},
number = ,
volume = 43:6,
place = {United States},
year = {Fri Mar 15 00:00:00 EST 1991},
month = {Fri Mar 15 00:00:00 EST 1991}
}