  A one dimensional model of the magnetic multipole volume plasma source has
been developed for use in intense ion/neutral atom beam injectors. The model
uses plasma transport coefficients for particle and energy flow to create a
detailed description of the plasma parameters along an axis parallel to that of
the extracted beam. Primarily constructed for applications to neutral beam
injection systems on fusion devices, the model concentrates on the hydrogenic
isotopes but can be extended to any gas by substitution of the relevant masses,
cross sections and rate coefficients. The model considers the flow of fast
ionizing electrons that create the ratios of the three hydrogenic isotope ion
species, H+, H2 +, H3 + (and similarly for deuterium and tritium) as they flow
towards the beam extraction electrode, together with the production of negative
hydrogenic ions through volume processes. The use of detailed energy balance in
the discharge allows the determination of the fraction of the gas density that
is in an atomic state and also the gas temperature as well as the electron
temperatures and plasma potential. Comparisons are made between the results of
the model and experimental measurements in deuterium from a number of different
filament driven sources used on beam heating facilities.

Plasma Physics