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Title: Comment on 'Shock-wave-induced enhancement of optical emission in nitrogen afterglow plasma'

Abstract

Sieffert et al. [Phys. Rev. E 72, 066402 (2005)] have recently presented experimental results on optical emission enhancement at the front of shockwaves propagating in nitrogen afterglow. They claim that their results point to local heating of electrons at the shock front. In this Comment it is shown that the observed emission enhancement can be explained on the basis of a commonly accepted model of nitrogen discharge and afterglow, so that the use of unfounded assumption of local electron heating is not required.

Authors:
 [1]
  1. Institute for High Temperatures, Russian Academy of Sciences, Moscow 125412 (Russian Federation)
Publication Date:
OSTI Identifier:
21072286
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. E, Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics; Journal Volume: 75; Journal Issue: 1; Other Information: DOI: 10.1103/PhysRevE.75.018401; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; AFTERGLOW; ELECTRONS; EMISSION; NITROGEN; PLASMA; PLASMA HEATING; SHOCK WAVES; WAVE PROPAGATION

Citation Formats

Naidis, G. V. Comment on 'Shock-wave-induced enhancement of optical emission in nitrogen afterglow plasma'. United States: N. p., 2007. Web. doi:10.1103/PHYSREVE.75.018401.
Naidis, G. V. Comment on 'Shock-wave-induced enhancement of optical emission in nitrogen afterglow plasma'. United States. doi:10.1103/PHYSREVE.75.018401.
Naidis, G. V. Mon . "Comment on 'Shock-wave-induced enhancement of optical emission in nitrogen afterglow plasma'". United States. doi:10.1103/PHYSREVE.75.018401.
@article{osti_21072286,
title = {Comment on 'Shock-wave-induced enhancement of optical emission in nitrogen afterglow plasma'},
author = {Naidis, G. V.},
abstractNote = {Sieffert et al. [Phys. Rev. E 72, 066402 (2005)] have recently presented experimental results on optical emission enhancement at the front of shockwaves propagating in nitrogen afterglow. They claim that their results point to local heating of electrons at the shock front. In this Comment it is shown that the observed emission enhancement can be explained on the basis of a commonly accepted model of nitrogen discharge and afterglow, so that the use of unfounded assumption of local electron heating is not required.},
doi = {10.1103/PHYSREVE.75.018401},
journal = {Physical Review. E, Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics},
number = 1,
volume = 75,
place = {United States},
year = {Mon Jan 15 00:00:00 EST 2007},
month = {Mon Jan 15 00:00:00 EST 2007}
}
  • This paper reports measurements of optical emission enhancement at the shock front of Mach 1.5 to Mach 3.5 shockwaves propagating in the afterglow of a 0.75 Torr nitrogen glow discharge. Electrically-generated shocks pass through the afterglow and create noticeable enhancements of the B {sup 3}{pi}{sub g}-A {sup 3}{sigma}{sub u}{sup +} and C {sup 3}{pi}{sub u}-B {sup 3}{pi}{sub g} transitions of nitrogen. Under our discharge conditions, the electron Debye length was approximately the same magnitude as the shock thickness; this allows the possibility of a space-charge region extending beyond the neutral shockwave discontinuity. Previous researchers have measured enhancement in the Bmore » {sup 3}{pi}{sub g}-A {sup 3}{sigma}{sub u}{sup +} optical emission at the shock front, but only in the active discharge. Fibers connected to photomultipler tubes measure the optical emission from the discharge. Laser deflection measures the shock velocity. The data reveals that the emission enhancement increases with Mach number, and also indicates that the emission enhancement decreases exponentially with time in the afterglow. Since the discharge voltage has already been shut off, the energy needed to create the emission enhancement cannot come from the power supply. We conclude that under our discharge conditions there is an increase in the already non-equilibrium energy of the electrons at the shock front via a shockwave-induced strong double layer.« less
  • No abstract prepared.
  • Kinetic modeling of propagating and stationary normal shocks in nonequilibrium nitrogen afterglow plasma is used to simulate the results of shock emission measurements in nitrogen afterglow. Emission intensity overshoot behind the shock predicted by the model is in satisfactory agreement with the experimental results and is consistent with previous analytic estimates. The model demonstrates that the first and the second positive band emission overshoot behind the shock are produced by energy transfer processes among the triplet electronic states of nitrogen generated in the electric discharge. On the other hand, charge separation and ambipolar electric field produced across the shock layermore » do not result in electron heating and additional electron impact excitation of electronic states. The calculations show that emission overshoot makes possible accurate detection of a stationary shock layer in supersonic flowing afterglow experiments.« less
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  • In laser shock cleaning (LSC), the shock wave is generated by laser-induced breakdown of the ambient gas. The shock wave intensity has thus been a factor limiting the performance of the LSC process. In this work, a novel method of amplifying a laser-induced plasma-generated shock wave by the breakdown of a liquid column is proposed and analyzed. When the laser beam is focused on a microscale liquid column, a shock wave having a significantly amplified intensity compared to that generated by air breakdown alone can be generated in air. Therefore, substantially amplified cleaning force can be obtained. The dynamics ofmore » a shock wave induced by a Q-switched Nd:YAG laser was analyzed by laser flash shadowgraphy. The peak pressure of the laser-induced shock wave was approximately two times greater than that of air breakdown at the same laser fluence. The proposed method of shock wave generation is expected to be useful in various applications of laser shock processing, including surface cleaning.« less