a pressure vessel surrounding the outside wall of {TAIL ~ the reaction chamber}, thus forming {HEAD ~ a first annulus} 
a pressure vessel surrounding the outside wall of { TAIL ~ the reaction chamber } , thus forming { HEAD ~ a first annulus }
OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD