Plasma sheath behavior in a total nonambipolar radio frequency generated plasma electron source

A Radio Frequency (rf) plasma-based electron source that does not rely on electron emission at a cathode surface has been constructed. Total nonambipolar flow is achieved when all of the random electron flux incident on an exit aperture is extracted through an electron and all of the ion flux incident on an ion sheath is extracted. This situation occurs within the electron source device when the ratio of the ion loss area to the electron loss area is approximately equal to the square-root of the ratio of the ion mass to the electron mass, and the ion sheath potential drop at the chamber walls is much larger than Te/e. The Nonambipolar Electron Source (NES) has an axisymmetric magnetic field of ∼100 gauss at the extraction aperture that results in a uniform plasma potential across the aperture, allowing for the extraction of all the incident electron flux without the use of grids. A prototype NES has produced 30 A of continuous electron beam current, using 2 sccm Xe, 1200 W rf power at 13.56 MHz, and 180x gas utilization. NES could replace hollow cathode electron sources in a wide variety of spacecraft and terrestrial applications.