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