LHC Report: Preparing for 4 TeV
After more than two months since its stop in December, the LHC is slowly coming back from its hibernation - even if the temperature of the magnets in the tunnel has actually been getting lower and lower in recent days. The tunnel has been crowded with hundreds of people, busy with maintenance activities and preparations for the restart. The end of most activities (and the access to the tunnel) is scheduled for 21 February. On this date, the Operations team will take back ownership of the machine from the Programmed Stops Coordination team and push forward the preparations for the beam.
The cool-down of all LHC sectors (left floating at around 80 K during the Christmas break) restarted three weeks ago. At present, more than half of the machine is at nominal cryogenic temperature and the completion of the cool-down is expected by 27 February. As soon as a sector is cold, the Electrical Quality Assurance (ElQA) team starts the high-voltage qualification of the superconducting circuits, to check insulation and instrumentation integrity. These qualifications were initiated on the first Sector available (Sector 23) during the Charmonix workshop week, and have since been carried out on three other Sectors (Sectors 56, 67 and 78) without any non-conformity being found.
Once the circuits have undergone the high-voltage qualification, the powering tests of the superconducting circuits begin. These tests officially started on 10 February, after the validation and preparation of the first sector. To minimize the impact on the activities requiring access to the tunnel (which will continue for a few more days), the powering tests are only being performed during the evening and at night, to cope with the safety constraints. These tests aim at pushing the performance of all LHC circuits to their operational level. The tests involve injecting current through the superconducting circuits while checking the correct behaviour of the protection mechanisms, an essential element for the safe operation of the machine. After operating at 3.5 TeV for two years, the LHC is entering another domain, with the main dipole and quadrupole circuits powered at a different current level for operation at 4 TeV.
Apart from some small issues and debugging (also of the new tools used this year to improve the performance in test execution), as at the beginning of each restart after a long stop, the tests are progressing well. All superconducting circuits should be commissioned during the first week of March. A few days of machine check-out will then drive us to the first beam, planned for 14 March.
Mirko Pojer for the LHC Team
LHC performance workshop summary
The Chamonix workshop last week reviewed the performance of the LHC in 2011 and discussed plans for 2012 and beyond. Among other things, we can look forward to the LHC running at 4 TeV during 2012.
A critical review of 2011
The performance of the machine was examined during the workshop, identifying possible improvements to critical systems such as beam instrumentation and machine protection. The high-intensity beams that the LHC collided last year have raised issues around the ring including beam-induced heating of some hardware, and problematic vacuum spikes. The present understanding of these problems and possible solutions were presented.
One of the big successes of 2011 was the squeeze - the reduction of the beam size at the interaction point - that was pushed in the latter part of the year. Squeezing even further in 2012 might be possible in combination with the use of tighter collimator settings. This could give a peak luminosity of around 6x1033 cm-2s-1 compared with a maximum of 3.6x1033 cm-2s-1 in 2011.
Possibilities for 2012
Steve Myers, CERN's Director for Accelerators and Technology, presented a summary of the workshop recommendations for the 2012 run. In brief, the LHC should operate at 4 TeV, with the key priorities being: delivering enough luminosity (of the order of 15 fb-1) to ATLAS and CMS to allow them to independently discover or exclude the Higgs; the proton-lead ion run; and a machine development programme that targets operation after the long technical shutdown. A run extension was not ruled out if necessary to meet the target integrated luminosity.
Machine availability should be improved in 2012 thanks to a number of mitigation measures taken during the Christmas stop. These include a number of measures aimed at reducing the effects of radiation on the electronics situated in the LHC tunnel.
Plans for the long shutdown of 2013/2014
The total length of the long shutdown (LS1) for the LHC is provisionally around 20 months. The main focus will be the splice consolidation work, which involves opening every magnet interconnect in the ring, and measuring carefully the resistance of each joint in the cables which carry the current between the dipoles and quadrupoles in the arcs of the LHC. It is currently estimated that 15% of the splices will be re-done; shunts and clamps will be installed across each splice. The aim is to definitively exclude the possibility of a repeat of the incident of 19 September 2008 at the highest energies expected at the LHC.
Besides this, each of the LHC experiments has extensive programs of maintenance and upgrades. Some of the key LHC systems (cryogenics, vacuum, quench protection, electrical distribution, cooling, ventilation, access and RF) will undergo major maintenance and improvements.
The machine after LS1
After LS1, a large number of re-training quenches of the LHC dipoles will be required in order to reach the nominal energy of 7 TeV per beam. Therefore, the beam energy in the first years after LS1 is expected to be around 6.5 TeV. The planned injector upgrades will not have been deployed at this stage, but the injector performance still looks capable of supplying sufficient beam quality to enable the LHC to reach the design luminosity of 1x1034 cm-2s-1. Potential limitations to post-LS1 performance (quenches, radiation to electronics, UFOs) were also considered.
Prospects for the LHC Injector Upgrade project and its principal client, the High-Luminosity LHC (HL-LHC), were also considered. Tentatively scheduled to start operation around 2023, HL-LHC aims to provide an ambitious 200 to 300 inverse femtobarns per year. An examination of the challenges of the HL-LHC included a look at the state of R&D for the new magnets required for the high-luminosity interaction regions.
There was also an entertaining look at the even more distant future. Possible future projects under consideration include the Large Hadron electron Collider (LHeC), which involves colliding 60 GeV electrons with 7 TeV protons, and the High Energy LHC (HE-LHC), in which the beam energy of the LHC is increased from 7 to 16.5 TeV. Serious technological challenges exist for both these options.
Steve Myers, CERN Director for Accelerators and Technology, and Sergio Bertolucci, CERN Director for Research, discuss the Chamonix workshop:
by Edited by Katarina Anthony based on regular reports by Mike Lamont, the Bulletin's correspondent from Chamonix