LS1 Report: short-circuit tests

As the LS1 draws to an end, teams move from installation projects to a phase of intense testing. Among these are the so-called 'short-circuit tests'. Currently under way at Point 7, these tests verify the cables, the interlocks, the energy extraction systems, the power converters that provide current to the superconducting magnets and the cooling system.


Thermal camera images taken during tests at point 4 (IP4).

Before putting beam into the LHC, all of the machine's hardware components need to be put to the test. Out of these, the most complicated are the superconducting circuits, which have a myriad of different failure modes with interlock and control systems. While these will be tested at cold - during powering tests to be done in August - work can still be done beforehand.

"While the circuits in the magnets themselves cannot be tested at warm, what we can do is verify the power converter and the circuits right up to the place the cables go into the magnets," says Matteo Solfaroli, co-coordinator of the short-circuit tests. "By placing a copper block before the cables make the transition to cold, it is short-circuited and tests can be carried out at warm."

The motivation behind these tests is two-fold: not only does testing these circuits now give us additional time to react in the event of a problem, it is also  safer for the engineers. When the powering tests are done at cold, access is restricted as there is a risk of helium release. By testing at warm, the time spent in the tunnel at cold is dramatically reduced.

During LS1, numerous interventions were made to the circuit's energy extraction system and water-cooled cables. Some were fixed and others were completely replaced. "In order to verify that the replacements can handle the long run of the machine, we bring the circuits to the ultimate current," says Mirko Pojer, co-coordinator of the short-circuit tests. "This is the highest current the power converters can achieve, and is actually higher than the nominal current in the machine. We run it through the local circuit system for a testing period that varies between a few hours and 24 hours, depending on the nature of the intervention carried out and the type of system."

Of course, where you have currents that can reach as high as 13,000 A, things are bound to get hot! Although expected, the team needs to verify if the warm-up stabilises to a manageable temperature that does not affect the behaviour of the cables. To do this, they use infrared cameras (see photo) to periodically check the temperature rise of the different parts of the circuit.

Thanks to the seamless collaboration between the Electrical Power Converter Group (TE-EPC), the Machine Protection and Electrical Integrity Group (MPE) and EN-EL, who are in charge of the cables, the short-circuit tests have progressed well. Tests should be completed by the end of July, in preparation for the powering tests in August. Points 4R and 6 have already been completed, with tests at Point 7 currently ongoing.

Meanwhile, elsewhere

In the LHC, all activities continue to progress well. Preparation is under way for the cool-down of the first sector of the machine, which will start on 7 May.

Over in the injectors, hardware commissioning across the PS complex (including the PS Booster) has progressed with no major issue. In the PS Booster, a wire scanner (BI.SMH) needs to be replaced. This will be done at the beginning of May and will unfortunately delay the start of cold checks. Happily, this will only be a short three-day delay, thanks to the excellent collaboration between teams.

The LS1 coordination team would like to take this opportunity to thank all the voluntary guides who have given "visits for CERNois" of the LHC tunnel. Thanks to your efforts, around 500 of your colleagues have had the pleasure of exploring the machine.


by Katarina Anthony