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