PEP-II and BaBar: End of a Remarkable Era
This past week draws to a close the running of PEP-II, ending nine extraordinarily successful years of operation. For many, it was a last chance to spend time in the Babar and PEP-II control rooms, watching in admiration as the two mega-facilities combined seamlessly to deliver the last batch of data, while at the same time establishing one new PEP-II performance milestone after another.
And so it was that I arrived last Tuesday evening in the Babar control room around 5:30 pm to soak up the enthusiasm and mastery of the two cracker-jack, swing-shift operations teams. Shortly after I arrive, 1.65 amperes of electrons are jerked from their stable orbit in the high energy ring. A pre-recorded message, "HER beam lost," reverberates menacingly through the control room. An intense flurry of activity ensues as the two operations teams, separated by half a mile, move into a precisely choreographed set of actions to restore data taking as swiftly as possible. The Babar crew, shift Leader Gerard Bonneaud from France and Data Quality Manager Adam Wren from England, leap into action. A terse, “essentials only” phone call to SLAC’s Bill Wisniewski , who is occupying the Babar Liaison slot in the Machine Control Center (MCC), is followed by an orderly termination of the data recording. A series of essential detector subsystem checks is made and within a minute of the beam loss, Babar is ready to commence data taking.
Unseen by us except through the myriad of electronic signals shipped from the accelerator control system and displayed on a series of monitors at Babar, the PEP-II operators diagnose the fault, thrust the HER injection system into high gear and begin refilling the 1,760 electron bunches. Notwithstanding the violent loss of the electron beam, the 2.6 amperes of positrons have remained orbiting stably in the low energy ring. A scant 10 minutes after the beam loss, data-taking has recommenced at maximum luminosity and low backgrounds. The two Babar Run Coordinators, Georg Marks from Germany and Jacques Chauveau from France, smile—their admiration for what the PEP-II operations staff has just done, and do day-in-day-out, is clearly reflected on their faces. Data taking has been restored—PEP-II and Babar are ticking away in perfect unison, each executing an enormously complex set of technical feats, pushed up hard against the edge of feasibility. Clearly I am observing “factory” performance.
There are no more losses of beam on the shift: in fact the beams stay in collision uninterrupted for the next fifteen-and-a-half hours!
Around 10 pm I ride over to MCC to view the "show" from the beam operator’s perspective. Engineering Operator In Charge, Geoff Milanovich, presides over the multitude of functions that are coordinated through MCC. There is frequent interaction with the on-site maintenance crews as they respond to control-room concerns or proactively tweak the subsystem hardware to ensure maximum performance. Both LCLS and PEP-II beams are running tonight and each program must be optimized for ultra-high efficiency. Lauren Alsberg is operating the linac and PEP-II injection chain, Robin Gold is in charge of the LCLS beams, and Sean Kalsi the PEP-II rings. I am fortunate to be at MCC to witness the operators execute a planned change in the collision energy of PEP-II. It is challenging enough to imagine how complicated colliding two multi-ampere beams is; to increase the energy of one of the beams without interruption of collisions, is even more remarkable to contemplate. Yet with only two requests from the control system by Sean, the move to higher energy with maximum luminosity and low backgrounds, is accomplished in two minutes! I watch in awe as the feedbacks fight successfully to counteract the energy change, dynamically adjusting machine component settings to accommodate the new orbit.
I left for home exhilarated by my evening’s experiences. The sophistication and level of performance of the accelerator and control systems at PEP-II is truly astounding. For nine years, the SLAC PEP-II team, the accelerator operations group, all the facilities maintenance groups, the downtime technical staff and those countless others that helped maintain and improve the machine have exhibited incredible innovation, ingenuity and dedication. You can all be immensely proud of what you have achieved both for particle physics and accelerator physics. I remain in awe of you all.
Jonathan Dorfan, SLAC Today, April 7, 2008