LHC portal

Is the purpose of the beam commissioning to bring beams back to the way they were in 2015, or are machine development investigations also being carried out to see what's possible for 2016?

Cheers,

JMc

It is even a step earlier than that. Commissioning brings the machine back to a point where beams with a low number of bunches can safely be injected, ramped up, squeezed and collided. Over the winter shutdowns, various components could have failed, or changed their parameters slightly. The machine operators have to verify that everything is still working, and tune many parameters to determine the best possible beam orbit in the ring.

2015 was very useful, of course - the luminosty with stable beams should increase much faster this year, so we could reach that performance within a month or two. Pushing the limits will then be done with stable beams and in dedicated machine development blocks.

mfb wrote: 2015 was very useful, of course - the luminosty with stable beams should increase much faster this year, so we could reach that performance within a month or two. Pushing the limits will then be done with stable beams and in dedicated machine development blocks.

Do you work on the LHC by any chance?

Since they're aiming to run at 40cm this year, I'd expect them to match last year's performance within two-three weeks; reaching twice the performance after six weeks. This should then give a performance average of approx 2fb/week for the remaining fifteen weeks.

Ohtherwise, they're going to be hard-pushed to achieve 25fb this year bearing in mind that they lose a week after each technical stop when restarting:

https://espace.cern.ch/be-dep/BEDepartm ... e_2016.pdf

Regards,

JMc

jmc2000 wrote:Do you work on the LHC by any chance?

Not on the machine, but for one of the experiments.

Since they're aiming to run at 40cm this year, I'd expect them to match last year's performance within two-three weeks; reaching twice the performance after six weeks. This should then give a performance average of approx 2fb/week for the remaining fifteen weeks.

A smaller beta* needs a larger crossing angle, so you don't gain a factor of 2 from it.

If no problems occur, we probably reach the end 2015 performance after something like 4 weeks (~1-2/fb) and get 2-3/fb until MD1/TS1. Going a bit beyond that, ~10/fb until MD2 are realistic. That leaves 11.5 weeks with 1.5/(fb*week) to reach the goal of 25-30/fb.

It is perfectly possible that some issues delay this schedule.


2-3/fb will be very interesting for the diphoton excess (a bit less data than 2015, but even if it just appears with 2 sigma in 2016 it is a really big thing), 10/fb should either give a clear discovery or a clear exclusion.

Update: We had the first stable beams over the weekend, a bit earlier than planned. First 3, then 12 bunches, so the luminosity was tiny (0.05% to 0.35% of the design value), but it also means scrubbing starts today, 3 days earlier than planned.

mfb wrote:Update: We had the first stable beams over the weekend, a bit earlier than planned. First 3, then 12 bunches, so the luminosity was tiny (0.05% to 0.35% of the design value), but it also means scrubbing starts today, 3 days earlier than planned.

Do you know if the first stable beams were squeezed to beta= 40cm?

Jmc

Yes they were.

Pileup was already significant. The low luminosity was mainly from the low number of colliding bunches (2 and 8), and LHCb and ALICE needed lumi leveling.