Transport of electron bunches in a magnetized plasma

Krasovitskii and Dorofeenko have found the conditions for self-focusing of a strongly modulated electron beam in a dense plasma. The effect occurs if the modulation frequency of the bunches ωm = 2πν/l (here ν and l are the velocity and spatial period of the beam modulation) is less than the plasma frequency ωp = (4πe2np/m)1/2 (here np is the plasma density and e and m are the electron charge and mass), and the dielectric permittivity var-epsilon = 1 - ωp2/ωm2 < 0 changes the sign of the Coulomb interaction between electrons in the bunches. In other words, the modulated electron beam creates moving potential wells in the plasma in which the electron bunches are confined by the excess ion charge of the plasma. Here the authors investigate the effect of an external magnetic field on the conditions for transport of a modulated beam in a plasma. The magnetic field manifests itself in changes in the waveguide properties of the plasma and the action of the Lorentz force F = (e/c)[vB] on the electrons of the bunches. In a longitudinal field, F = 0, the plasma anisotropy produces an increase in the bunch radius without changing the longitudinal dimensions. The appearance of a transverse magnetic field component B perpendicular is accompanied by a displacement of the beam electrons due to the force F, i.e., an analog of the Hall effect in a conductor. But since the boundaries of the conductor at which charge accumulates are absent here and the role of the walls is played by the smoothly decaying potential of the bunch at its periphery, the result of a constant force acting on the current is to empty out part of the electrons from the potential wells