Why are the Tevatron fill times so long?

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Discussion Overview

The discussion revolves around the long fill times of the Tevatron, which range from 15 to 20 hours, despite a theoretical optimum of around 8 hours. Participants explore the reasons behind the extended fill times, including machine performance, risks associated with attempting shorter fills, and the impact on integrated luminosity.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants note that the optimum fill time is not steep, suggesting that attempting to shorten it could lead to mechanical failures, which would prolong the process.
  • One participant references a document indicating that the peak store duration is 23 hours, with a minimal effect (10%) from a 6-hour shift, supporting the rationale for longer fills.
  • Concerns are raised about the frequency of magnet quenches occurring during the process of putting a store in, which could justify avoiding more frequent fills.
  • A participant questions the relevance of the data presented in the slides regarding integrated luminosity for shorter fill times, indicating a need for more specific information.
  • Another participant mentions that the luminosity lifetime varies as beams decay and disperse, which could influence decisions on fill times.
  • Antiproton production rates are also suggested as a factor in determining optimal fill times.

Areas of Agreement / Disagreement

Participants express various viewpoints on the reasons for the long fill times, with no consensus reached on the optimal strategy. Multiple competing perspectives remain regarding the impact of fill duration on performance and the associated risks.

Contextual Notes

Limitations include the dependence on specific definitions of luminosity and the uncertainty surrounding the effects of magnet quenches on fill time decisions. The discussion also highlights the variability in luminosity lifetime as a factor in optimizing fill times.

jason12345
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The Tevatron is being run with fill times of between 15-20 hours, with a beam half life of 6 hours and machine turnaround times of around 5 hours. Theoretically, the optimum fill time should be around 8 hours, so why are they using fill times so much longer?
 
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Because it's not a very steep optimum, and sometimes things break when you try and shoot again, so there's always a risk it will take longer. If you're running, it's a good idea to keep running as long as you can.
 
Vanadium 50 said:
Because it's not a very steep optimum, and sometimes things break when you try and shoot again, so there's always a risk it will take longer. If you're running, it's a good idea to keep running as long as you can.

Have you worked on an accelerator where this has been a reason? If not, I'll send an email asking about this.

The Tevatron is working so well with these consistent long fills that it'd be interesting to find out just what the difference in integrated luminosity is between 10 and 20 hour fills.
 
Take a look at http://www.c-ad.bnl.gov/pac2011/proceedings/talks/moocn2_talk.pdf" , slide 18, "Optimizing the Store Duration". The red line is relevant. It peaks at 23 hours, but a 6 hour shift makes only a 10% effect.

Also look at slide 15, where it points out that almost half of the magnet quenches (57 vs. 68) occur when putting a store in. That's a good reason to avoid doing this more often than necessary.
 
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Vanadium 50 said:
Take a look at http://www.c-ad.bnl.gov/pac2011/proceedings/talks/moocn2_talk.pdf" , slide 18, "Optimizing the Store Duration". The red line is relevant. It peaks at 23 hours, but a 6 hour shift makes only a 10% effect.

Also look at slide 15, where it points out that almost half of the magnet quenches (57 vs. 68) occur when putting a store in. That's a good reason to avoid doing this more often than necessary.

Thanks for the link to the slides, looks interesting. Slide 18 doesn't show the the integral luminosity for 0 - 15 hours where you can say if a 6 or a 15 hour fill will make much of a difference, which is what I'm after.

Slide 15 is for 1200 stores, 154 quenches, which means close to 1 in 20 quenches occur when putting a store in. To me, that shouldn't have much of an effect on the fill time chosen.

Alexander Valishev kindly emailed me:

Luminosity life time is not constant but increases as the beams
decay and disperse. See e.g.
http://accelconf.web.cern.ch/AccelConf/p05/PAPERS/TPAP038.PDF

For a description of the store length optimization refer to
http://accelconf.web.cern.ch/AccelConf/PAC2009/papers/mo4rac03.pdf

The antiproton production rate is a factor in deciding the fill time.
 
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