The Sciences

Beam Circulating in LHC Again!

Cosmic VarianceBy John ConwayNov 20, 2009 8:43 PM


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09:37 PST: Like many of my colleagues, I've been eagerly awaiting word that the LHC has successfully threaded the proton beam around the whole ring. In recent days they have gotten it half way around the 27 km circumference, and within hours, they should be able to circulate it and I assume "capture" it with the RF, which creates stable bunches in the synchrotron. Everything has gone very smoothly to this point, so I expect success shortly! Once beam has circulated stably in both rings, some time next week the LHC team will attempt to collide protons at the injection energy of 450 GeV (a total center of mass energy of 900 GeV). While this is much less than the Tevatron is colliding presently, it could provide some sorely needed initial data for the detectors to do timing and calibration of the various subsystems. There will even hopefully be a few collision events recorded with clear "dijet" structure - collisions where quarks and/or gluons inside the protons hit head on and effectively bounce sideways into the detector, giving two back-to-back collimated sprays of particles. Pictures of such events will be great to see, at long last! You can follow progress live on twitter: and I will update this post as I learn more. 10:32 PST: The LHC has gotten beam around clockwise, to Point 6! Woo hoo! 10:45 PST: Magnet quench - should be recovered soon... 11:25 PST: Beam has reached Point 7! 11:30 PST: Point 8! Next beam will be sent past Point 1 where ATLAS is... 11:39 PST Beam all the way around the ring! WOO HOO!! It's baaaaaack! The LHC Page 1 display shows that the injection probe beam made it more than once around the machine:

11:54 PST: Next goals: do the same with the counterclockwise beam. Will they attempt RF capture tonight? Trying to find out... 13:11 PST: Turns out (no pun intended) they decided to go for RF capture of the clockwise beam rather than probe counterclockwise. They are up to 10 million turns with the RF on! Fantastic! 13:30 PST: Having captured the beam for several minutes, the LHC will now switch to counterclockwise. 14:53 PST: About to go for a full orbit of the counterclockwise beam...done!! Now to RF capture! 15:30 PST: Counterclockwise beam is RF captured! The LHC is operational...colliding beams within a week? Stay tuned.

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