Development of a field desorption ion source for neutron generator applications

Field desorption is a process in which external electric fields are used to promote the ionization and ejection of atoms chemisorbed on the outer surface of an electrode. This process occurs in the presence of a high electric field (10-40 V/nm) and can be used to desorb hydrogen or its isotopes from a metal substrate, producing 100% atomic ions in the high field region surrounding the emitting surface. Electrostatic modeling and simulations have been performed to study design parameters for nanoscale metal desorption tips intended to be used in a high density emitter arrays as a field desorption ion source within a sealed tube neutron generator. The radius of the emission tip and the proximity of the emitting cone to the edge of the gate hole are of particular importance; for maximal desorption region fields the optimal position of the emission tip is within the plane of the gate film. An important design challenge is to ensure fields at the tip are sufficient for desorption while ensuring fields at the gate are not large enough for electron emission.