Experiments on injecting electrons into helical magnetic field configuration

An experimental study on injecting an electron beam into a helical vacuum magnetic field via stochastic (chaotic) magnetic field region has been conducted on the compact helical system device. Remarkably, despite being launched from the outside of the last closed flux surface (LCFS), the injected electrons move across the LCFS and, moreover, penetrate deeply into the magnetic surfaces. This penetration of electrons occurs in a collisionless process that has never been observed in past studies on toroidal nonneutral plasmas confined in axisymmetric geometry. Data clearly suggest that the stochastic magnetic region, which confines a considerable number of electrons, plays a key role in the observed collisionless penetration.