Electrical Breakdown in Low-Pressure Nitrogen in Parallel Electric and Magnetic Fields

Abstract

The influence of magnetic field on electrical breakdown characteristics for low- pressure nitrogen discharges is investigated by applying a magnetic field B parallel to the electric field E. Paschen curves were obtained (at a fixed value of d and variable p) and the secondary electron emission coefficient (γ), the first Townsend ionization coefficient (α) and the ionization efficiency (η), were plotted with respect to the variation of the reduced field (E/P). To observe the effect of the magnetic field these curves were plotted for fixed values of B=0 T and B=0.072 T. A Helmholtz coil was used to produce a uniform magnetic field (B) parallel to the discharge axis. We observed that the magnetic field B applying along the discharge axis promoted a reduction of the breakdown voltage .The breakdown is facilitated by the magnetic confinement of electron which reduces the electron losses and effectively increases the collision frequency between electrons and the gas particles at a given reduced field, thus increasing the ionization efficiency. The presence of the axial magnetic field does not lead to the variation of Townsend coefficients significantly at the conditions of the B-field and reduced field E/P investigated. Overall it is concluded that the DC electrical breakdown of the gases is facilitated if a longitudinal magnetic field is applied along the discharge axis.