How can the intensity be increased?

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jmc2000
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Joined: Sun May 08, 2011 2:51 pm

How can the intensity be increased?

Post by jmc2000 » Sat Jun 11, 2016 11:00 pm

Fill 5013 is another record, yet at constant number of bunches. How are they increasing the intensity, and where can I see the corresponding parameter?

Cheers,

JMc

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terryburton
Posts: 13
Joined: Thu Mar 11, 2010 11:44 am

Re: How can the intensity be increased?

Post by terryburton » Sun Jun 12, 2016 1:24 am

You might find the following calculator interesting, especially the INPUT parameters and the formulae in the OUTPUT section: https://lpc.web.cern.ch/lpc/lumi2.html

I think that this paper provides a quite accessible introduction to how each of these parameters contributes to the resulting luminosity: https://cds.cern.ch/record/941318/files/p361.pdf

These parameters can be changed by updating the filling scheme, but otherwise remain fixed between fills:
  • Colliding bunch pairs
    Number of bunches per beam
These parameters are effectively fixed by the machine's current configuration since they require re-calibration of the machine optics and protection systems after updating:
  • Revolution frequency
    Beam energy
    Beta*
    Full crossing angle
This parameter can be used to reduce luminosity as required:
  • Separation in separation plane
Fixed by nature:
  • Particle mass
    Process cross section
These can be controlled and optimised from fill to fill as is happening at the moment:
  • Bunch population
    Normailised transverse emittance
    Bunch length
The evolution of the beam emittance and bunch length can be seen in the injector performance statistics: https://acc-stats.web.cern.ch/acc-stats/#lhc/injectors

An indication of the instantaneous emittance is can be seen on the "Dashboard" Vistar: https://op-webtools.web.cern.ch/vistar/ ... CDASHBOARD

The bunch population isn't reported directly but can be derived from the total intensity / number of bunches in the ring.

The usual strategy is to work up to the maximum number of bunches for the machine's configuration, spend time optimising the injector chain to provide a low and repeatable emittance and then push up the bunch population. During a production run (such as 2016) the goal is to optimise the total integrated luminosity, i.e. to maximise the amount of collisions data in the experiments. A balance must be sought between achieving high reliability (maximising time spent in stable beams, minimising the outage and turnaround time - roughly what is referred to as the "Hübner factor"), increasing initial beam luminosity and improving beam lifetime.

RocketManKSC
Posts: 37
Joined: Mon Mar 29, 2010 10:09 pm
Location: Titusville Florida

Re: How can the intensity be increased?

Post by RocketManKSC » Sun Jun 12, 2016 3:42 am

I always wondered why the actual time should not be longer then the number given by 7.1.2 Optimization of integrated luminosity. I seams that you need to know what the probability that you will actually run that long on the next run if you dump this run. I f you have a good chance of only running an hour would be better to keep running.

mfb
Posts: 168
Joined: Sat Oct 03, 2015 7:58 pm

Re: How can the intensity be increased?

Post by mfb » Sun Jun 12, 2016 10:55 am

Unplanned dumps in stable beams are usually at random times and don't depend much on the previous time in stable beams. The risk to lose the next fill after an hour is not much larger than the risk of losing the current fill after an hour. Sure, it has to be taken into account because it makes the average run time shorter.

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