Late last year the Large Hadron Collider collided its first protons at a record-breaking energies. On December 16, the collider shut down so teams could prepare the machine to run at even higher energies in 2010. So what are the scientists, engineers and technicians at CERN doing during this approximately two-month-long "technical stop?"
The goal of the many activities taking place during the technical stop is to prepare the LHC to accelerate beams to an energy of 3.5 TeV. The three main tasks are replacement of about 4000 connectors in the quench detection system; testing components of the new quench protection system to bring it to full functionality; and maintenance for the CMS experiment.
The LHC’s superconducting magnets are kept at the very low temperature of 1.9 K in order to carry the high currents needed to bend fast-moving particles. At a beam energy of 3.5 TeV, 6000 amps of current will flow through the LHC's main bending magnets, the dipoles. A quench occurs when part of the superconducting cable within a magnet heats up and can no longer conduct electricity without resistance. The first line of defense against quenches is detection using a complex electronics system that monitors the magnets and surrounding technology.
One main task for the technical stop is the replacement of some connectors in the new quench detection system’s 250 km of high-voltage cable. The connectors, initially installed in 2009, are being replaced after it was discovered that they were easily damaged if cables were bent.
Once a quench is detected, the stored energy must be safely channeled away from the magnet. The new quench protection system, installed in November, includes about 10,000 new cables designed to de-energize specific sectors of the LHC in the event of quenching. The updated system also incorporates better programming and electronics to detect quenches. The software and equipment for this system are being tested during this technical stop to ensure that everything is functioning properly for this year's maximum beam energies.
The last main task for the current stop is to replace 272 corroding portions within the CMS detector’s yoke endcaps that were causing the detector's water cooling lines to fail.
The technical stop should be completed by mid-February, and beam is expected back in the LHC shortly afterward.
For more details, read the articles in the CERN Bulletin or CMS Times, or watch today's episode of LHC News, which focuses on the quench protection system.
by Daisy Yuhas
