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Title: Collisional absorption of laser light in under-dense plasma: The role of Coulomb logarithm

In this work, we re-examine collisional absorption of 800 nm wavelength laser pulses in under-dense plasma. For a given temperature and density of the plasma, most of the conventional models of the electron-ion collision frequency ν{sub ei}, with a Coulomb logarithm independent of the electron-ponderomotive velocity, show that ν{sub ei} and the corresponding fractional laser absorption α remain almost constant (or decrease slowly) up to a value I{sub c} of the peak intensity I{sub 0} of the laser pulse, and then ν{sub ei} and α decrease as ≈I{sub 0}{sup −3/2} when I{sub 0} is increased beyond I{sub c}. On the contrary, below some temperature (≲10 eV) and density, with a total-velocity (thermal velocity plus the ponderomotive velocity) dependent Coulomb logarithm, we find that ν{sub ei} and α grow hand in hand up to a maximum value around I{sub c} followed by the conventional I{sub 0}{sup −3/2} decrease when I{sub 0}>I{sub c}. Such a non-conventional anomalous variation of α with I{sub 0} was observed in some earlier experiments, but no explanation has been given so far. The modified Coulomb logarithm considered in this work may be responsible for those experimental observations. With increasing temperature and density, the anomalous behavior is found to disappearmore » even with the modified Coulomb logarithm, and the variation of ν{sub ei} and α with I{sub 0} approach to the conventional scenario.« less
Authors:
 [1]
  1. Institute for Plasma Research, Bhat, Gandhinagar 382 428, Gujarat (India)
Publication Date:
OSTI Identifier:
22252156
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 21; Journal Issue: 1; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ABSORPTION; ELECTRON-ION COLLISIONS; LASERS; PEAKS; PLASMA; PONDEROMOTIVE FORCE; VELOCITY; WAVELENGTHS