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12Complex Systems of Charged Particles and their Interactions with Electromagnetic Radiation 2016
EFFECT OF ANISOTROPY OF ELECTRON VELOSITY DISTRIBUTION IN PLASMA
ON THE FREQUENCY AND DAMPING OF POTENTIAL SURFACE WAVES
Yu.M. Aliev, K.Yu. Vagin, S.A. Uryupin, A.A. Frolov*
P.N. Lebedev Physical Institute of RAS, Moscow, Russia, e-mail: uryupin@sci.lebedev.ru,
vagin@sci.lebedev.ru
*Joint institute for High Temperatures RAS, Moscow, Russia, e-mail: frolov@ihed.ras.ru
Gas ionization in the field of laser radiation creates nonequilibrium plasma in which velocity distribution of photoelectrons differs substantially from Maxwellian. In the strong radiation field, such plasma forms on a time scale that is several orders of magnitude shorter that the characteristic times of collisional relaxation of the photoelectron distribution function, plasma expansion, and the development of aperiodic instability. Therefore, there is a relatively long time interval within which the nonequilibrium photoionized plasma exists and its properties should be investigated.
In this report we analyze surface potential waves in photoionized plasma in which velocity distribution of photoelectrons created by tunnel ionization of atoms in the field of a linearly polarized radiation is approximated by an anisotropic bi-Maxwellian electron distribution. The dispersion relation for surface potential waves in semi-infinite photoionized plasma under the assumptions that the distribution function of photoelectrons is an even function of the velocity and that electrons undergo mirror reflection from the plasma boundary was found. The dispersion relation for the case of a bi-Maxwellian distribution of photoelectrons is derived in an explicit form. The dependences of the frequency and damping rate of a potential surface wave on the wavenumber and the degree of anisotropy of electron distribution characterized by different temperatures along and across the plasma surface are established. The frequency and damping rate of surface potential waves are numerically calculated. The calculations are complemented by relatively simple approximate formulas. A qualitative difference of the influence of electron thermal motion along and across the plasma surface on dispersion and damping characteristics of the potential surface waves is revealed. The influence of electron motion along the plasma surface is similar to the influence of thermal motion on the bulk Langmuir waves. On the contrary, thermal electron motion across the surface leads to qualitatively new dependences. Contributions to both the dispersion relation and the damping rate proportional to the effective thermal velocity across the surface appear in the range of relatively small wavenumbers. When electrons move predominantly across the surface, their thermal motion leads to reverse dispersion and the damping rate decreases with increasing wavenumber.
This work was supported by the Russian Foundation for Basic Research, project no. 15-0207490.
