What is turn-around time of accelerator? I was looking today through pdg table of collider parameters and I saw that some turn-around time for LHC is $\approx 200$ min. I tried to search on it, but everywhere it is kind of assumed that you already know what it is. In pdg review on accelerator physics, it was barely mentioned in Tevatron description 

The route to high integrated luminosity in the Tevatron was governed by
  the antiproton production rate, the turn-around time to produce another store, and the
  resulting optimization of store time

Could anyone explain to me what does this turn-around time means? 
 A: From the paper that estimates the mentioned number:
"In  the  following  we  define  the  turnaround  time  of  an  accelerator  storage  ring  as  the  time  between  the  end  of   one   and   the   start   of   the   next   physics   run.   For   an    accelerator    storage    ring     the    measurement    of    the     turnaround time starts with the beam at top energy of the  accelerator  and  comprises  the  ramp  down  of  the  magnet   system  to  the  injection  energy  settings  after  the  beam
extraction,  the  time  required  for  setting  up  the  machine   for the next injection, the time required for injecting new  beams  into  the  machine,  the  time  required  for  the  beam   acceleration  (ramp),  the  optics   transition  for  the  physics  run  (squeeze)  and  the  time  required  for  adjusting  the   beam conditions so that the detectors can start again data  taking."
Source: https://cds.cern.ch/record/1133125/files/p34.pdf
Essentially, it's the amount of time you need to stop the beam and start it again. The reason this is necessary is because, as particles collide, the intensity of the beam starts decreasing; at some point, the intensity (and therefore the collision rate) drops to the point where it would be more efficient to just stop, dump the rest, and refill the beam, rather than continue on collecting data at a lower rate. The precise point at which this happens is determined by how much time you lose when you have to stop and restart (i.e. the turn-around time).
