Breakdown of gases in crossed electric and magnetic fields with loss mechanisms

Abstract

The paper is concerned with the importance of electron and ion losses in uniform-electric-field breakdown in gases at low pressure. The function of a transverse magnetic field and the walls of the containing vessel in increasing these losses is investigated. Measurements are described of static breakdown potentials in hydrogen, helium, nitrogen and argon in a configuration of crossed electric and magnetic fields, where particles are swept to the walls by the E×B drift. The construction of the discharge tube is described. The design is intended to ensure a uniform electric field which is everywhere crossed with an azimuthal magnetic field produced by the current in a central conductor. The criteria adopted for the definition of breakdown are discussed, and curves of breakdown potential as a function of gas pressure and magnetic field are presented for the four gases in the pressure range from a few millitorr to about 500 mtorr. Break-down potentials are shown to be increased very significantly by the magnetic field. Simple quantitative arguments are presented which suggest that gross deflection of the initiatory avalanches to the walls is probably the main loss mechanism causing the increases in breakdown potential. The precise mechanism by which final breakdown occurs is not understood.