LHC Report: getting in shape for the Run 2 marathon

The buzzword you'll hear most both inside and outside the CCC is "training". Rather than preparation for an athletic competition, it actually refers to the way the LHC is trying to get in shape for the long Run 2 marathon at 6.5 TeV.


Picture 1: progress of LHC superconducting circuit commissioning.

In the previous edition of the Bulletinwe discussed the lengthy process of commissioning LHC superconducting circuits and the phenomenon of repetitive quenches accompanying the progressive increase in their performance. This is typical for superconducting magnets, but it is particularly intriguing for the LHC dipole magnets. Not only because each and every one of the 1,232 dipoles has to reach the same current target in order for beams to circulate at a certain energy (the weakest link of the chain determining or compromising the performance of all the others), but also because we know that every additional quench brings us closer to our 2015 objective.

All the dipole magnets have been tested - one by one - in SM18, but this is the first time that they will all be trained together up to the current that corresponds to 6.5 TeV energy (namely 10,980 A) in the tunnel.

Picture 2: Training quenches of the LHC dipoles.

Every morning, people arriving at the CCC ask “where are we with the training in sector XY?”, and they look at the colourful plot (see Picture 2) to try and guess how long it will take to complete the full training of that sector.

Aside from the guesswork, people are continuing to work hard to prepare the machine in time and the powering tests are now very much in the ramp-up phase. Currently, more than half of the test steps have been executed. Also, importantly, the dipole circuits in three out of eight sectors have been trained to the 6.5-TeV-equivalent current, with the total number of quenches confirming the initial prediction of about 100 quenches for all the dipoles in the machine. An additional fourth sector is now in the training stage. Among the already-trained sectors, sector 5-6 is reaching the target energy for a second time: in 2008, tests were conducted in that sector, bringing it above 6.6 TeV.

Testing of all other magnet circuits has progressed well and an entire sector has been fully commissioned, with all its circuits having been brought up to 6.5 TeV at the same time.

On Wednesday, 11 February at point 4 (sector 3-4), the teams in charge of the ELQA tests performed the final high-voltage qualification of an LHC main dipole insulation as part of an extensive series of LS1 interventions and upgrades. They applied 1500 V to the circuit and observed no significant leakage of current, which concludes the scheduled campaign of electrical tests positively.

Powering tests are ongoing on six different fronts, with the last two sectors arriving at the beginning of next week. The tremendous effort of the many teams that worked tirelessly during LS1 to prepare the circuits is almost over. The Electrical Quality Assurance (ELQA) team is one of the last; it has been an integral part of the process since the very beginning of LS1, guaranteeing the quality of the extensive consolidation and ensuring that the cool-down of all elements was done correctly and didn’t generate any issues. They recently completed their last planned verification, although their expertise will undoubtedly be required to address inevitable non-conformities.

The whole machine will be soon in the hands of the beam commissioning team for one last sprint. The preparation for the marathon is entering its final stage.

by Mirko Pojer & Matteo Solfaroli