Neutral beamline with improved ion energy recovery

Claim 1

In a neutral particle beam injector system wherein a neutral particle beam is generated and directed along a beamline, including a substantially ground-potential-operated ion source from which ions of a selected isotopic species are accelerated to a desired kinetic energy level along said beamline through a neutralizer, said neutralizer being operated at a selected ion acceleration potential relative to said ion source to provide said desired kinetic energy level and wherein a significant portion of said ions are converted into energetic neutral particles together with electrons, full kinetic energy atomic ions and fractional kinetic energy atomic ions derived from molecular ions of said selected species accelerated into said neutralizer, an ion energy recovery system including a magnetic field generating means for producing a magnetic field (B) transverse to said beamline in a beam exit region at the beam exit end of said neutralizer and of sufficient strength to substantially block electrons from exiting said neutralizer and deflecting said full energy ions from said beamline along a separate path, and at least one ground potential full energy ion charge collector surface disposed in the path of said full energy ions deflected from said beamline for collecting the charge from said full energy ions directed to said ion collector, the improvement in said ion energy recovery system comprising; an electrically conductive, nonmagnetic, ground potential operated box-like structure surrounding a portion of said beam exit end of said neutralizer and insulatably spaced from said neutralizer, said box-like structure having a downstream end surface disposed transverse to said beam exit end of said neutralizer, said end surface of said box-like structure having an opening in a central region thereof for restricted passage of said neutral particle beam and said full energy ions from said exit region of said neutralizer so that the rmaining downstream end surface of said box-like structure produces a strong electric field gradient (E f ) in conjunction with the accelerating voltage applied to said neutralizer which is transverse to said magnetic field (B), thereby forcing said fractional energy ions to be deflected back into said neutralizer and forcing any electrons in said beam exit region between said neutralizer and said end surface of said box-like structure to drift in a direction perpendicular to said electric field (E f ) and said magnetic field (B) within said box-like structure; and an electron collector disposed within said box-like structure, said electron collector surrounding and extending past said exit end of said neutralizer into the drift path of said electrons, said electron collector being disposed in an insulatably spaced relation to said neutralizer and said box-like structure and biased sufficiently positive with respect to said neutralizer to collect said electrons forced to drift toward said electron collector.