2016 should be a standard long year:
- ~150 days of proton physics including intensity ramp-up (down from 160 at start 2016 following schedule review)
- Intensity ramp-up - assume 4 weeks
- Planning on nominal 25 ns beam from the injectors - figures based on 2015 experience shown below
- Usual caveats apply - integrated totals will be largely driven by availability.
- BCMS in 2015 tested but compromised by presence of e-cloud - consider as back-up option to be explored further in 2016
Assumed parameters
| Parameter |
Chamonix 16 |
Actual - July 16 - BCMS |
|
| Energy [TeV] |
6.5 |
6.5 |
|
| Bunch spacing |
25 ns |
25 ns |
288 bunches per injection following TDI replacement |
| β* (1/2/5/8) [m] |
0.4 / 10 / 0.4 / 3 |
0.4 / 10 / 0.4 / 3 |
Tested in 2015 - 0.5 m also an option |
| Ext. half X-angle (1/2/5/8) [μrad] |
-185 / 200 / 185 / -250 |
-185 / 200 / 185 / -250 |
10 sigma in 1&5 assuming 3.75 micron emittance |
| Number of colliding bunches (1/5) |
2736 nominal 25 ns |
2076 |
Limited by SPS dump to 96 bpi as of July 16 |
| Bunch population |
1.2e11 |
1.18e11 |
|
| Emittance into Stable Beams [μm] |
3.5 |
2.6 |
|
| Bunch length [ns] - 4 sigma |
1.25 |
1.05 |
Start of fill |
| Peak Luminosity (L0) [cm-2s-1] |
1.1e34 |
1.1e34 |
BCMS could give around 1.4e34 |
| Peak mean pile-up (inel xsection 80 mb) |
29 |
39 |
cf. ~40 with BCMS |
| Average mean pile-up |
~25 |
27 |
|
| Average luminosity lifetime (tau) |
20 hours |
24 hours |
|
- Taking the fill length distribution from 2015 - phase 2 25 ns ramp-up (56 days)
- fit to an Erfc
- taking the product with L0exp(-t/tau) - values above
- scaling from 56 (2015) to 150 (2016) days and factoring in the ramp-up (3-4 weeks)
- one gets around 31 fb-1 for the year
- (As a rough consistency check - naive application of 2012's Hubner factor (0.18) gives 26 fb-1 for the year).
Time in Stable Beams:
Assumption at start of year:
- the 2012 physics efficiency was around 37%.
- A number of issues affecting this number have been addressed (e.g. R2E, vacuum non-conformities), however running at 6.5 TeV brings additional challenges (hardware nearer limits, lower tolerance to beam loss etc.). 25 ns brings e-cloud, higher UFO rates.
- It would seem reasonable at this stage to assume a similar physics efficiency for 2016. Thus 0.37*150 days = 55.5 days = 4.8 million seconds.
- Operation in 2015 seems to support this assumption - reasonable availability despite being a commissioning year and having to face virgin e-cloud and UFOs. We had around 32% physics efficiency during phase 2 of the 25 ns ramp-up.
Update 29th July 2016
- Astounding availability and few premature dumps From just after the first technical stop we have enjoyed 84% availability combined with very few premature dumps. To 22 July - 67% time in Stable Beams (physics efficiency).
- As of 29th July - around 72 days proton physics left (the possibility of dropping a week is to be discussed). The rest of the year is somewhat choppy (MD, technical stop, special physics runs) - let's assume 60% physics efficiency: another 3.7 million seconds.
- Since 11 June: 15 fb-1 delivered - around 340 pb-1/day.
- Assuming 60% Stable Beams and similarly availability gives ~20 fb-1 additional integrated luminosity between 1st August and 1st November.
Updated July 2016 - Mike Lamont
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