Excitation of Electrostatic Waves Near Electron Cyclotron Harmonic Frequencies

Abstract

The problem considered is that of excitation of electrostatic waves in a plasma in a magnetic field by non-relativistic fast electrons. The plasma is assumed to be uniform and to have a velocity distribution that differs slightly from Maxwellian by the presence of the fast electrons. Collisions and ion motion are neglected. The "dressed"-test-particle approach is used to calculate the electric field in the plasma associated with the fast electrons and, from this, the energy lost by the fast electrons. The Fourier decomposition of the energy-loss rate gives the spectrum. The electrostatic dispersion relation limits the emission (by Landau damping) to directions nearly perpendicular to the magnetic field. Solutions of the dispersion relation for these directions are presented, and typical emission lines for monoenergetic fast electrons are shown. For a suitable choice of fast-electron velocities, the positions and widths of the peaks are shown to agree with experimental observations of electromagnetic emission.