LHC reboot: the world’s largest particle accelerator is now active

LHC reboot: the world’s largest particle accelerator is now active


The Large Hadron Collider is reborn — on Easter weekend, of course. After shutting it down for two years in February 2013, the world’s biggest and most powerful particle accelerator is up and running again. That doesn’t mean that it’s going at full power though, says Paul Collier, head of beams at CERN. Getting it to the acceleration needed to collect collision data — and perform actual physics experiments — is going to take two months.


“It’s not like flipping a switch, that’s for sure,” Collier says. CERN’s physicists first have to increase the machine’s energy over time. “We’re talking early to mid-June, when we can take the first high energy data, [but] at this stage the collision rate will be fairly low,” he says. “The next stage, which is done in parallel with data taking, is to steadily increase the number of protons.” Increasing the number of protons means increasing the number of collisions inside the machine, and the temperature therein. By the end of 2015, the energy of the particle beams circulating inside the LHC will have reached their peak — an energy that has never before been achieved by a particle accelerator.

The Large Hadron Collider (LHC) is a $10 billion particle accelerator in Geneva, Switzerland. Its operation led to the discovery of the Higgs Boson, an elementary particle, in 2012. The finding — which is still being debated — filled in the last major gap of a 40-year-long quest to complete the Standard Model of particle physics, one of physics’ most important theories.

Still, the Standard Model is an incomplete theory. Another theory, called supersymmetry, suggests there is an undiscovered partner particle for each one in the Standard Model. Those proposed particles are among those that scientists at CERN hope to detect now that the LHC has been rebooted. One predicted particle is called a “dark matter particle.” Dark matter is a mysterious and invisible substance — it doesn’t absorb, emit or reflect light — that physicists say makes up 26 percent of our universe. Because of the changes that were made at the LHC, researchers now think that it might be possible to create the particle that constitutes dark matter, and infer its presence from the amount of energy that’s “missing” after a particle collision occurs. Particles aren’t all, though: LHC scientists will also be looking out for evidence of exotic phenomena like rolled-up dimensions and tiny black holes.


The LHC was shut down in 2013 because 10,000 electrical interconnections between the machine’s supercooled magnets needed to be reinforced. “We basically spent two years reinforcing these junctions, such that they can withstand anything that we can throw at them in terms of the energy of the machine,” Collier says. The last few months have been spent cooling the machine down — the LHC operates at 1.9 Kelvin, or -456 Fahrenheit  — and checking all the electrical circuits to make sure that there aren’t any issues.

The LHC’s reboot was actually planned for earlier in the year, but a short circuit affecting one of the magnets delayed the activation. “We hope it’s a minor problem with one of the circuits,” Collier told last week, before the issue was resolved on March 31st.

“What we’ve put together is almost a new machine,” Collier says. “And, of course, we’re also booting it into a new regime in terms of the power of the machine — the energy at which the beams collide.” Because of the changes that the scientists made, the LHC is now 60 percent more powerful than it was in 2012. “Nobody has ever been here before, so that in itself is very exciting.”


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