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​After two years of intense maintenance and consolidation, and several months of preparation for restart, the  (LHC), the most powerful particle accelerator in the world, is back in operation. On 5 April at 10:41 a.m., a proton beam was back in the 27-kilometre ring, followed at 12:27 p.m. by a second beam rotating in the opposite direction. These beams circulated at their injection energy of 450 GeV. Over the coming days, operators will check all systems before increasing energy of the beams.

"Operating accelerators for the benefit of the physics community is what CERN's here for," said CERN Director-General Rolf Heuer. "Today, CERN's heart beats once more to the rhythm of the LHC."  

"The return of beams to the LHC rewards a lot of intense, hard work from many teams of people," said the head of CERN's Beam Department, Paul Collier. "It's very satisfying for our operators to be back in the driver's seat, with what's effectively a new accelerator to bring on-stream, carefully, step by step."

The technical stop of the LHC was a Herculean task. Some 10,000 electrical interconnections between the magnets were consolidated. Magnet protection systems were added, while cryogenic, vacuum and electronics were improved and strengthened. Furthermore, the beams will be set up in such a way that they will produce more collisions by bunching protons closer together, with the time separating bunches being reduced from 50 nanoseconds to 25 nanoseconds.

Read more on the  website.