Fermilab TodayFriday, December 2, 2005  
Crash Course in Luminosity, Key to Discovery at Fermilab
The two graphs show how improving the supply of pbars to the collider (graph 1) has coincided with an increase in luminosity (graph 2) from 2002-2006. (Click on images for larger version.)

Rapid Response Team Set To Cap Off Run II Upgrades
Like any "overnight success," the Accelerator Division's Rapid Response Team has been years in the making. The groups pushing the accelerated finishing touches to Run II upgrades have origins going back to early 2003, soon after Roger Dixon was named division head. Dixon wanted to draw people from different areas, forming teams that could respond quickly to unexpected problems. One such team successfully tackled difficulties at the Switchyard on the 120 GeV beamline.

"This is a bigger effort, more like a really long-term investment," said Dave McGinnis, head of the Run II Upgrade Rapid Response Team. "The key issue was making more antiprotons. The antiproton stacking rate didn't seem to be keeping pace. We didn't want to wait for a crisis, so last summer, we pulled together different groups in AD. We put together special groups for the Antiproton Source, the Main Injector, the Recycler, the Booster and the Tevatron. We broke all the issues down into tasks, and then we really focused our efforts."

McGinnis, Associate Division Head for Accelerator Systems, emphasized the Rapid Response Team's difference from a standing SWAT-type team: teams and team members change depending on the challenge, and anyone can be selected as a leader. In this case, McGinnis was tapped for his experience as a former head of the Antiproton Source. The team has approximately 20 members and meets twice a week to chart results and strategy.

Their overall focus, as in the focus for the upgrades, was increasing luminosity in the Tevatron by increasing the number of antiprotons. The three-part strategy comprises increasing the antiproton production rate; providing a third stage of antiproton cooling with the Recycler; and increasing the transfer efficiency of antiprotons to the Tevatron. The Rapid Response Team focused on one of the three limiting factors to luminosity: the number of antiprotons.

The Rapid Response Team worked to push Run II upgrades that had been installed into operational mode, and to push other upgrades onto a fast track. Ioanis Kourbanis, Bill Pellico and Jim Steimel led in dealing with Main Injector and Booster issues, using slip-stacking to deliver more protons to the antiproton target. "They've gotten phenomenal results," McGinnis said. Keith Gollwitzer is leading on antiproton collection and issues with beam aperture; Paul Derwent; on antiproton cooling; and Elvin Harms, on rapid transfer to the Tevatron.

All the efforts received a critical contribution from dedicated machine studies, which the team identified as a priority from the start. "Director Pier Oddone asked what we needed, and we said a dedicated study period for a single goal," said McGinnis. "It's meant an exponential step in the time devoted to studying the machines."

It's also been where Jim Morgan has played an important role. Morgan's responsibility is to coordinate accelerator activities, including delivering beam to experiments, studies and repair work. He has to maximize the amount of useful beam the experiments receive (luminosity for CDF and DZero, protons on target for NuMI, MiniBoone and SY120), while making progress with accelerator studies. He has to make some key decisions.

"Studies are generally geared toward finding ways to improve accelerator performance," Morgan explained. "Study time reduces the amount of beam we can deliver to the experiments on the short term, so it is important to understand the long term cost/benefit of each study. The accelerator departments generally prioritize their studies themselves, with oversight from Dave and myself. Dave and I both firmly believe that accelerator studies should be geared toward providing more beam to the experiments. Studies that are proposed with no overall practical benefit to the experiments are much less likely to receive study time."

Ironically, having the Tevatron currently down for repairs, even with neutrino and fixed-target experiments to support, has been a benefit for the priority of addressing the antiproton stacking rate. "We are using this period of Collider downtime, when pbars aren't needed, to accomplish a long list of studies in support of improving the pbar stacking rate," Morgan said. "A large part of the increases in integrated luminosity over the past two years can be traced to increasing the amount of pbars reaching low beta in the Tevatron. By increasing the rate at which pbars are accumulated, we can increase the number of pbars in the Tevatron and integrated luminosity to CDF and DZero. We're hoping to make significant progress in shortening their list of studies during this down period."

Morgan's reference to integrated luminosity raises the ultimate measure of success for the upgrades. With increasing numbers of antiprotons available, the Tevatron has set repeated records for initial luminosity over the past several months. Average integrated luminosity per week has also increased by approximately a factor of five since January 2003. "Integrated luminosity is what the experiments need," McGinnis said. "All the upgrades have to be sustainable, for the long run."

Integrated luminosity is a function of time, so time will tell the final story.

-Mike Perricone

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