Nonambipolar electron source

Abstract

A radio frequency (rf) plasma-based electron source that does not rely on electron emission at a cathode surface has been constructed. All of the random electron flux incident on an exit aperture is extracted through an electron sheath resulting in total nonambipolar flow within the 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 100G at the extraction aperture that results in a uniform plasma potential across the aperture, allowing the extraction of all the incident electron flux without the use of grids. A prototype NES has produced 15A of continuous electron current, using 15SCCM (SCCM denotes cubic centimeter per minute at STP) Ar, 1200W rf power at 13.56MHz, and 6 times gas utilization. Alternatively 8A of electron current can be produced, using 3SCCM Ar at 1200W rf and 20 times gas utilization. NES could replace hollow cathode electron sources in a wide variety of applications.