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