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pcatom wrote:Having a lower Beta* would just mean that more separation would be needed to keep the luminosity reasonable.

Lower Beta* means the beam is thinner at IP. The thinner the beam, the higher luminosity (collision probability increases) and the finer tuning you need to steer beams to intersect just partially.
So higher Beta* both reduces luminosity on its own and makes it easier to fine-tune the luminosity by beam steering to match target.

Fingers crossed for some test collisions during the present fill.

PhilG wrote:Fingers crossed for some test collisions during the present fill.

There were collisions midnight CERN time.

Does anyone know what the "intermediate energy run" is and what it is for? They have planned it for a few days some time in April.

does anyone know why the beam intensity plots have swapped from being a nice line trace to being all spiky and, effectively, a filled in histogram?

The spikes go to 4E15 protons which seems a little high to me and could possibly be noise in the measurement system however that is mere speculation.

Edit: no panic - they have changed it back. It would still be interesting to know the whys and wherefores

B.

The intermediate energy run will be at 2.76TeV (1.38TeV/beam) which is the same center of mass collision energy per nucleon as the Pb run.

Lead has 82 protons and 126 neutrons. The run last year was at a proton equivalent energy of 3.5TeV/beam, ie 3.5TeV per proton. The total energy per ion was therefore 82x this value (287 TeV) and the energy per nucleon was this divided by 208 (ie 1.38 TeV). The run at this energy is needed for cross-calibration purposes between proton and lead collisions.

For the problem with the beam current on page1, the fast BCT had a bit of a brainstorm it seems.

@pcatom, thanks for the explanations

PhilG wrote:@pcatom, thanks for the explanations

Ditto. Especially thanks for the explanation of lead energy levels, always puzzled me a bit that did, explanation is obvious it turns out

This is copied from the CERN bulletin at http://cdsweb.cern.ch/record/1335119


LHC Report: Towards stable beams and collisions

Over the past two weeks, the LHC re-commissioning with beam has continued at a brisk pace. The first collisions of 2011 were produced on 2 March, with stable beams and collisions for physics planned for the coming days.

Low intensity beams with just a few bunches of particles were used to test the energy ramp to 3.5 TeV and the squeeze. The results were successful and, as a by-product, the first collisions of 2011 were recorded 2 March.

One of the main activities carried out by the operation teams has been the careful set-up of the collimation system, and the injection and beam dump protection devices. The collimation system provides essential beam cleaning, preventing stray particles from impacting other elements of the machine, particularly the superconducting magnets. In addition to the collimation system, also the injection and beam dump protection devices perform a vital machine protection role, as they detect any beam that might be mis-directed during rare, but not totally unavoidable, hardware hiccups. In order to ensure this task is performed properly, they have to be carefully positioned with respect to the beam.

Teams were also busy preparing the bunch trains to be injected from the SPS into the LHC. The bunch spacing planned for this year is 75 ns and over the last days, operators have injected batches of 8 bunches with the nominal spacing. This is the first step towards the planned total of around 900 bunches per beam during the year.

The aim for the coming days is to complete the collimator set-up through the squeeze and in conditions for physics. After verification that everything is as it should be, the way will be open to first collisions and 'stable beams'. Initial runs will be with three widely-spaced bunches per beam as careful checks that everything is set-up properly continue.

Todays morning report indicates that they are waiting on a decision to start stable beams. The collimator and beam dump have to give the all clear. http://lhc-commissioning.web.cern.ch/lh ... eting.pptx

If we see stable beams today it may be a sign that they are about ready to move to the next phase. They will soon start the ramp up in luminosity towards the record levels of last year and possibly beyond. According to the outline sxhedule shown at Chamonix, this process could be realized in as little as two weeks if everything goes well.

We have stable beams

Multi bunch injections yesterday looked very smooth.
The coordination page indicates that they will start running with stable beams and increasing bunch numbers from Wednesday. Everything is following the planned schedule nicely.
Yesterday I was watching live events from CMS but the muon trackers were not yet on. Other live displays were not functioning but perhaps some links have changed.

They have been running with 32 bunches for peak luminosities of 33/ub/s. Already about 1/pb has been collected to add to the 40/pb from last year

They managed a turnround of only 2.5 hours between runs, much better than last year.

Objective for the week is 100+ bunches.

Does any one know why they are going to stop the intensity increase to run at 1.3Tev for a few weeks?

tomey36, that question was answered by pcatom about 10 posts back in this thread.

64 bunches now circulating, preparing to ramp