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