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