Experiments on a New Acceleration Mechanism of Electrons

Abstract

Suprathermal electron production in laser fusion experiments is one of the most unfavorable effects because it degrades the target compression caused by increased preheating. Resonance absorption is one of the best known mechanisms for producing the suprathermal component of electrons. 1 However, when there exists in the resonance (or critical) layer a weak magnetic field which is applied externally or generated by the resonance absorption itself, the acceleration mechanism of electrons changes. Recent theoretical and experimental investigations revealed that a new mechanism named Vp× B acceleration (or Surfatron effect) is one of effective acceleration mechanisms which are responsible for producing high energy electrons, 2–7 where Vp is the phase velocity of an electrostatic wave, such as an electron plasma wave, and B is the magnetic field density applied externally. In this mechanism suprathermal electrons observed originally in the direction along the density gradient near the resonance layer, which are presumably accelerated by the localized field, are accelerated more strongly in the direction across the density gradient by applying a weak magnetic field (Ω/ω) ⪅ 10-2) perpendicular to the density gradient and to the plasma wave electric field, Where Ω is the electron cyclotron frequency and ω is the frequency of the applied rf field. The hot electron production has directionality with respect to the magnetic field and is restricted to narrow regions near the resonance layer and the region of slightly lower density side. 2