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Inverse bremsstrahlung cross section estimated within evolving plasmas using effective ion potentials

Published online by Cambridge University Press:  01 June 2009

F. WANG ,
E. WECKERT  and
B. ZIAJA
F. WANG
Affiliation:
Hamburger Synchrotronstrahlungslabor, Deutsches Elektronen-Synchrotron, Notkestraße 85, D-22603 Ham burg, Germany
E. WECKERT
Affiliation:
Hamburger Synchrotronstrahlungslabor, Deutsches Elektronen-Synchrotron, Notkestraße 85, D-22603 Ham burg, Germany
B. ZIAJA
Affiliation:
Hamburger Synchrotronstrahlungslabor, Deutsches Elektronen-Synchrotron, Notkestraße 85, D-22603 Ham burg, Germany Department of Theoretical Physics, Institute of Nuclear Physics, Radzikowskiego 152, 31-342 Cracow, Poland ([email protected])
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Abstract

We estimate the total cross sections for field-stimulated photoemissions and photoabsorptions by quasi-free electrons within a non-equilibrium plasma evolving from the strong coupling to the weak coupling regime. Such a transition may occur within laser-created plasmas, when the initially created plasma is cold but the heating of the plasma by the laser field is efficient. In particular, such a transition may occur within plasmas created by intense vacuum ultraviolet (VUV) radiation from a free-electron laser (FEL) as indicated by the results of the first experiments performed by Wabnitz at the FLASH facility at DESY. In order to estimate the inverse bremsstrahlung cross sections, we use point-like and effective atomic potentials. For ions modelled as point-like charges, the total cross sections are strongly affected by the changing plasma environment. The maximal change of the cross sections may be of the order of 75 at the change of the plasma parameters: inverse Debye length, κ, in the range κ = 0 − 3 Å−1 and the electron density, ρe, in the range ρe = 0.01 − 1 Å−3. These ranges correspond to the physical conditions within the plasmas created during the first cluster experiments performed at the FLASH facility at DESY. In contrast, for the effective atomic potentials the total cross sections for photoemission and photoabsorption change only by a factor of seven at most in the same plasma parameter range. Our results show that the inverse bremsstrahlung cross section estimated with the effective atomic potentials is not affected much by the plasma environment. This observation validates the estimations of the enhanced heating effect obtained by Walters, Santra and Greene. This is important as this effect may be responsible for the high-energy absorption within clusters irradiated with VUV radiation.

Type
Papers
Information
Journal of Plasma Physics , Volume 75 , Issue 3 , June 2009 , pp. 289 - 301
Copyright
Copyright © Cambridge University Press 2008

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