On April 5, after two years of refurbishment and upgrades, the Large Hadron Collider officially went back online: two proton beams firing in opposite directions around a 27-kilometer ring with an initial "injection energy" of 450 GeV, or about three times that of the Higgs boson decays reported in 2013. This initial energy plateau was maintained for several days as engineers tested and verified the tens of thousands of new consolidated electrical connections, new magnetic protection systems, and improved and strengthened cryogenic, vacuum, and electronics systems. On April 9, LHC engineers turned things up, reaching energies of near 6.5 TeV (6500 GeV).
This was the record, the highest energy ever achieved in a particle accelerator. LHC operators maintained it for about 30 minutes before "dumping" the beams into a thick graphite block. The current goal is maintaining dual beams that are safe and stable for several hours at a time, eventually reaching collision energies of up to 13 TeV. The coming weeks will consist of many more tests to ensure everything is working correctly and to further refine experimental parameters for the coming particle-hunting work.
"There may be, for example, problems keeping the beam stable, and we also don't know how many times the magnets will quench—or suddenly lose their superconducting state—while the beam is running," Giulia Papotti, a lead engineer at the LHC, ?told Symmetry. "It's experimental work. It's partly about knowing what we have to do and partly about solving unexpected problems. But everything we do is to make the experiments happy and let them take data safely."