Negative ion transport inside collisional presheaths.
Modeling of negative ion sources proposed for spallation sources or neutral beam injectors must include several ion production mechanisms, in particular, for wall production, the initially backward ion motion must be reversed in the presheath to obtain extraction. An adequate analytic simplification of the full Vlasov-Boltzmann equations to a one space dimension model for the investigation of the transport effects of the presheath voltage is described here. Integrodifferential collision dominated transport equations are written and solved for typical profiles of the presheath voltage. The results for space charge density improve previous estimates. A transverse magnetic field can be included in the formalism to treat electron transport: principles of its solution are summarized and numerical examples are given; plasma quasineutrality is approximately verified.
Cavenago
M
M
INFN-LNL, viale dell'Universitá n 2, Legnaro (PD), Italy. cavenago@lnl.infn.it