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BNL Accelerator Physicists Achieve Record Luminosities at RHIC

Accelerator physicists at the Relativistic Heavy Ion Collider (RHIC) are achieving record luminosities, or collision rates, during the ongoing run colliding deuterons with gold ions.

"Thanks to many improvements, during this run we can deliver in four days the same number of collisions we delivered in 10 weeks during the 2003 deuteron-gold run," said Wolfram Fischer, Deputy Head of the Accelerator Division in the Collider-Accelerator Department.

Improvements were made in almost all areas. To allow acceleration and storage, the deuteron and gold beams are not continuous, but packaged in "bunches." A vacuum system, upgraded over the last few years, allows the acceleration and storage of 93 instead of only 55 bunches, and improvements in the injector system allow more than 1 billion gold ions to be packed in a bunch, 40 percent more than in 2003. At the collision point, the beams are less than half the size they were in 2003. Significant progress was also made in controls, instrumentation, data analysis, and refrigerator efficiency. Last but not least, after many difficulties last year, the availability of all systems has visibly improved.

members of the accelerator physics team

Gathered in the Main Control Room with machine run coordinator Kip Gardner (front, center) are members of the accelerator physics team that achieved record improvements in luminosity at the Relativistic Heavy Ion Collider for the ongoing experimental run colliding deuterons with gold ions.

A significant portion of the increased luminosity is due to the physicists' ability to keep the gold ions tightly packed within the bunches, so that more ions collide as the two beams cross. This tricky accomplishment is a result of the successful implementation of something called "stochastic cooling" at RHIC. As in all charged particle beams, RHIC's ions tend to spread out - they heat up - as they circulate in the accelerator. RHIC physicists Mike Blaskiewicz and Mike Brennan have devised ways to measure this intrabeam scattering and send signals ahead of the racing beam to apply a corrective electric field that re-squeezes the beam when it arrives.

Said Fischer, "Every run is truly a team effort, which cannot be undertaken without the whole department. However, there are always some outstanding individuals. To name a few: Kip Gardner, the machine run coordinator, and Mike Sivertz, the scheduling physicist, coordinated the machine work and interface with the experiments essentially around the clock. Dejan Trbojevic's analysis of how small the beams can be made led to one of the largest luminosity increases compared to 2003, and his calculations were implemented by a large and dedicated team led by Fulvia Pilat. The work of Don Bruno, Wing Louie and their team reduced the power supply failure rate significantly. Accelerator physicists Todd Satogata and Vadim Ptitsyn, together with the operations teams, established an efficient operation. The record luminosities resulting from these and all the other contributions have made a great difference in the amount of data that the experimenters will have available."

2008-527  |  INT/EXT  |  Media & Communications Office