With the flip of a single red switch, the operators of the Large Hadron Collider cleared the last near-light-speed protons from the particle accelerator early this morning. Such "dumps," which divert the LHC's particle beams from their circulating ring and into two 10-ton graphite blocks, are routine. They can occur multiple times a day to protect the collider from beams that become unstable. But today's dump is expected to be the last one for two years, as physicists and engineers work to repair and upgrade the facility, with the aim of nearly doubling its power.
The coming campaign, dubbed "Long Shutdown 1," will span all 27 kilometers of the LHC's accelerator ring. The chief aim will be to fix some 10 170 high-current connections between superconducting magnets. A single faulty connection between two magnets was responsible for the explosion in September 2008 that destroyed part of the accelerator and set the LHC's schedule back more than a year.
In the aftermath of that accident, a careful investigation of the quality of other connections around the accelerator revealed additional faulty connections. Some of the most egregious ones were fixed, but LHC managers couldn't exclude the possibility that there were other large ones lurking in parts of the accelerator that were not warmed up for careful inspection after the accident. These were deemed not a danger, so long as the LHC did not operate at too high of an energy. As a result, the collider has been run at 3.5 TeV per beam (more recently 4 TeV), instead of the 7 TeV it was designed for.
CERN's Lucio Rossi, who headed up the production of the superconducting magnets, explained in a 2010 article from the CERN Courier that the magnet team estimated that 10-15 percent of the joints in the facility will need to be resoldered in order to make the collider safe to run as designed. Technicians will also add on an extra, copper shunt to each of the 10 000-odd interconnections. That will allow an extra pathway for electric current should a superconducting connection suddenly quench, or become normally conducting (this greatly raises the material's electrical resistance and can lead to overheating, which is what happened in 2008).
In addition to new joints, the LHC will also be getting new electronics shielding, new computers, and upgrades to the four large detector experiments stationed around the ring. "It's absolutely not time off," Dave Charlton, deputy spokesperson for the LHC's ATLAS experiment, told Nature.
Physicists will also continue to analyze the data collected over the three years that the LHC was in operation. There's still a lot of work to be done in pinning down the properties of the newly discovered, Higgs-like particle that was announced in July. And when I spoke with Joe Incandela, spokesperson for the CMS experiment, last year, he told me that the CMS team had been stockpiling data in anticipation for the shutdown. They hope to comb through it for evidence of still more new physics.
(Image: Maximilien Brice/CERN)