Heating of plasma electrons by laser light

Abstract

The heating of electrons in laser-irradiated plasmas is investigated from the quantum-mechanically extended collisionless Boltzmann equation, which has a term for the rate of the change in the electron distribution due to inverse bremsstrahlung. It is shown that the inverse bremsstrahlung cannot be investigated, in principle, by means of the Vlasov equation. The heating of the electrons is shown to consist of i) the Landau damping of the plasma waves, which are produced by the laser field (classical turbulent heating); ii) the microscopic quantummechanical interaction between each electron and the laser radiation under the influence of the plasma waves (collisionless inverse bremsstrahlung), and iii) the same mechanism as the collisionless inverse bremsstrahlung except that the plasma waves are replaced by the static plasma field (collisional inverse bremsstrahlung). It is found that the collisionless inverse bremsstrahlung is the dominant heating mechanism in laser fusion and is identified as the so-called anomalous heating mechanism. For the situation in which the laser field is weak and the plasma is collisionless, the collisional inverse bremsstrahlung, which is stronger than the collisionless one, is of the order of the classical turbulent heating. In this situation, the plasma field is calculated by the use of the fluid description of the plasma in order to include the finite-pressure effect on the stabilization of the plasma field.