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