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