An ion source has shorter central magnetic pole than {HEAD ~ regular closed drift ion source} with {TAIL ~ magnetic screens} that provide positive magnetic gradient in an ion sources discharge channel 
with
An ion source has shorter central magnetic pole than { HEAD ~ regular closed drift ion source } with { TAIL ~ magnetic screens } that provide positive magnetic gradient in an ion sources discharge channel
OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH