NEW HIGH-POWER FAST ATOM BEAM SOURCE

This article describes a new high-power fast atom beam (FAB) source incorporating an electromagnet. The electromagnet increases the total path length of electrons entering the source, enabling this source to produce higher plasma densities. Beam current densities up to 1 mA/cm2, which is about ten times that of a conventional FAB source, are obtained by using an electromagnet and a multiaperture grid. The beam current density can also be controlled by adjusting the flux density of the electromagnet and the gas pressure in the source. The beam neutralization coefficient is more than 90% almost independent of the flux density, discharge current, and source configuration. This coefficient does, however, strongly depend on the gas pressure of the FAB source, rapidly increasing as gas pressure increases. Most of the fast atoms have a kinetic energy about equal to the discharge voltage. Ions generated in the glow discharge are accelerated, and collisions with gas molecules near the cathode convert these ions into fast atoms without loss of kinetic energy.