The Large Hadron Collider has set a new energy record following a series of upgrades. This facility is the world's largest atom smasher. Test collisions carried out at the LHC reached 13 teraelectronvolts (TeV).
The LHC accelerates groups of subatomic particles in opposite directions around a massive ring before directing them into a collision course with each other. The latest test experiment utilized positively charged protons to test equipment designed to protect the detector from stray particles.
Following the two-year upgrade to the collider, the first beam, at 6.5 TeV, ran through the ring on April 10. That was followed by the first collisions, carried out at a lower energy level, 450 gigaelectronvolts (GeV).
"When we start to bring the beams into collision at a new energy, they often miss each other. The beams are tiny - only about 20 microns in diameter at 6.5 TeV; more than 10 times smaller than at 450 GeV. So we have to scan around - adjusting the orbit of each beam until collision rates provided by the experiments tell us that they are colliding properly," said Jorg Wenninger from the LHC Operations team.
Particles will continue to circle through the detector for several hours as the LHC team monitors the quality of the beams and evaluates the current set-up of the collider. Although the LHC is capable of steering up to 2,800 particle packets at a time, these collision tests are being carried out with just one or two bunches in each beam.
"We know how everything worked back in 2012, but a lot has changed since then, both with the machine and with the experiments as well. At this stage it's not telling us anything about new physics. Mainly it's helping us learn about the performance of our experiments," Dan Tovey of the University of Sheffield said. It ran at 8 TeV in 2012.
At the energies required for these experiments, electrical currents in the collider need to be extremely high - up to 12,000 amps. This requires superconducting cables which can lose their essential properties in the presence of just small amounts of stray energy.
"Superconductivity is a low-temperature phenomenon, so the coils have to be kept very cold, just 1.9 degrees above absolute zero to be precise, or about -271°C. Even a tiny amount of energy released into the magnet for any reason can warm the coils up, stopping them from superconducting," researchers at the collider reported.
The LHC was designed, in part, to determine which of two major cosmological theories are correct. Oddly, results showed results inconsistent with either theory. Physicists then determined they needed higher energies to solve the conundrum. This resulted in the collider being shut down and upgraded. The second run of experiments at the LHC are scheduled to begin early next month, after testing is completed.