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LHC Reaches Record Energy
toruonu writes "Yesterday evening the Large Hadron Collider at CERN for the first time accelerated protons in both directions of the ring to 1.18 TeV. Even though the 1 TeV barrier per beam was first broken a week ago, this marks the first time that the beam was in the machine in both directions at the same time, allowing possibly for collisions at a center of mass energy of 2.36 TeV. Although the test lasted mere minutes, it was enough to have detectors record the very first events at 2.36 TeV. LHC passes Tevatron (the particle collider at Fermilab that operates at 1.96 TeV) and becomes the highest energy particle collider in the world (so far it was effectively just the highest energy storage ring...)"
The reason to collide particles coming in from opposite directions is from kinematics. If you shoot a 1 TeV beam at a fixed target you only get roughly 50 or GeV as the center of mass energy (if I remember right it's ca sqrt(2*m_proton*1000)). That square root is a bitch there. If you shoot them head on to each other at equal energy, then you have the full energy at your disposal. Any other configuration will only reduce the effective energy. If I remember right the LHC dipole magnets are created in such a way that they automatically accelerate particles in parallel beamlines in opposite directions if the particles are of the same charge so it's a nice feat allowing for best efficiency. However you have to understand that the particles are effectively for your local observation traveling at the speed of light. They make ca 11500 circuits every second and you have to keep them in orbit. At the same time the bunch is made up of same charge particles that all want to get away from each other. So the technical difficulty is controlling the magnets in sync with the beams to keep them going and if you have two beams going in opposite directions it just become tougher. Hence the slow testing in baby steps (though they are in general huge steps I'd say). In general I hope some accelerator engineer can chime in and explain the precise background.