Trajectories of nonthermal electrons in the hot spot of a vacuum spark

Abstract

The trajectories of high-energy electrons in the inner part of a micropinch (hot spot) are calculated. It is shown that the collisionless electrons (born, for example, in the tail of Maxwellian distribution) drift to the pinch axis in the current-induced magnetic field and the inductive electric field to form axisymmetric orbits with radial oscillations and a shift along the z-axis to the anode (modified run-away). On average, the time when the electron moves chiefly across the z-axis exceeds the period of its movement along the discharge axis, hence the probability of exciting the ions is higher when the electrons have a relatively larger perpendicular velocity component. This can explain the experimental observations of polarization of x-ray lines emitted from hot spots in a vacuum spark. Modified run-away can also play a crucial role in the energy balance of the micropinch plasma.