An apparatus in accordance 6 wherein said supply means comprises an annular chamber surrounding said evacuation chamber, means for supplying said drive medium to said annular chamber under pressure and a ring nozzle means for feeding {HEAD ~ the drive medium} from said annular chamber to {TAIL ~ said evacuation chamber} at a supersonic speed 
to
An apparatus in accordance 6 wherein said supply means comprises an annular chamber surrounding said evacuation chamber , means for supplying said drive medium to said annular chamber under pressure and a ring nozzle means for feeding { HEAD ~ the drive medium } from said annular chamber to { TAIL ~ said evacuation chamber } at a supersonic speed
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