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