{HEAD ~ The next step} is pumping down {TAIL ~ the plasma cleaning chamber interior region} down to a pre determined pressure, with hydrogen as the ambient gas 
is pumping down
{ HEAD ~ The next step } is pumping down { TAIL ~ the plasma cleaning chamber interior region } down to a pre determined pressure , with hydrogen as the ambient gas
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH