Relativistic Electron Beam Tracking of Reduced Density Channels in Normal Density Air

A high-current relativistic electron beam injected into a uniform background gas will drive a significant return current in the beam induced background plasma. Interaction of the return current with the beam current can drive the beam off axis, possibly resulting in a disruptive beam instability such as the resistive hose. If the beam is injected into a cylindrical, reduced-density channel in normal density air, the return current will preferentially flow in the higher density edges of the channel. The dipole component of this return current distribution will produce a net centering or tracking force on the beam causing it to follow the density channel. This mechanism would provide a means of guiding a beam to a desired target as well as minimizing scattering and energy loss along the way. Preliminary results indicate that at least the first half of the SuperIBEX electron beam pulse has been seen to track the density channel.