Runaway electrons in an air gap in the presence of a magnetic field

Abstract

The divergence of the runaway electron flow generated in an air-filled discharge gap with a sharp conical cathode can be essentially reduced by applying a guiding axial magnetic field, which opens up prospects for the practical use of formed dense paraxial bunches of fast electrons. In the present work, we consider factors that determine the radial scale of the bunch. Our analysis shows that the main factor is the diffusion of electrons across the magnetic field lines due to collisions with gas molecules. Calculations of the dependence of the runaway electron beam radius on the magnitude of the applied magnetic field, taking this phenomenon into account, agree with the experimental data.