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