Beam 142 is interrupted by an injection mirror 144, which is positioned to intersect {HEAD ~ one half} of {TAIL ~ the beam} 142  
of
Beam 142 is interrupted by an injection mirror 144 , which is positioned to intersect { HEAD ~ one half } of { TAIL ~ the beam } 142
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH