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Another Retreat to Advance RHIC

By Fulvia Pilat

Since the beginning of RHIC operations in 2000, the RHIC Retreat has been the main forum to address the recent accelerator performance and prepare the next and future runs. Typically we hold it about 2 weeks after the end of RHIC operations, when run memories are still fresh, yet it is early enough for the Retreat discussions to be relevant in the planning of the machine shutdown.

The Retreat consists of 2 full days off site, where participation is by invitation, and an open summary session at BNL. One of the main objectives of a Retreat is to promote frank and constructive discussion among the participants beyond the scheduled agenda, so the venue is typically chosen to be far enough to encourage participants to stay but not too far to prevent day attendance. The main goals are the preparation of the next run and prioritization of work for the shutdown, and that cannot be achieved without an eye to the larger picture of the future plans for our facility. Attendance includes CAD staff and management, representative from the experiments, Laboratory management and a limited number of guests from other institutions, when warranted.

With the end of RHIC operations this year in mid March, the 2008 RHIC Retreat took place in Montauk, March 31-April 1 with a closeout session on April 2 in the Snyder Auditorium at the Laboratory. For more detailed information see the Retreat web page http://www.c-ad.bnl.gov/RHIC/retreat2008/ and click on “overall agenda” to access the full list of presentations.

Pictured above (from left): Fulvia Pilat addresses the RHIC Retreat, Derek Lowenstein, Chair of Brookhaven's Collider-Accelerator Department, and Wolfram Fischer of Brookhaven's Collider-Accelerator Department.

The Overview session was devoted to reviewing the performance of the past run and setting the goals for the next, in the context of the future plans for our accelerator complex and physics program, and of the even wider landscape of nuclear physics. Deuteron-gold operations were very successful this year as well as the short low energy run. Polarized proton operations reestablished Run-6 performance and that confirms that long runs are imperative to make progress with polarized beams. The input from our main ‘customers’, STAR and Phenix, both technical ad organizational, has been as always welcome, frank and therefore very valuable. The APEX program was successful in making new developments operational, in particular the beta squeeze, which resulted in significant luminosity improvement. Despite the ever-present budget uncertainties that very likely will postpone the start of RHIC operations to early 2009, the plans at the Retreat have been focused towards a long polarized proton run at 100 GeV and a short one at 250 GeV, and a Gold-Gold run at 100 GeV/u, the latter necessary to test the performance of transverse stochastic cooling, which after the successes of the longitudinal system, has become the main upgrade path for RHIC-II.

In the session focused on the preparation for the next run, we first reviewed all paths to luminosity improvements for ion operations. Besides the already mentioned stochastic cooling, we discussed the 56 MHz super-conducting cavity that when implemented, in a few years, will result in significant vertex improvements for the experiments. On the shorter time scale of next run, significant dividends can be paid by improving transition crossing, by further squeezing beta* in operations and by developing a lattice with tighter focusing in the arcs to counter intra beam scattering. We expect also progress by the careful monitoring and minimization of emittance both transverse and longitudinal. Excellent progress has already been in fact demonstrated this year in reducing the longitudinal emittance in AGS by better matching. We carefully reviewed the status of the polarized protons program, in the injectors, RHIC and in polarimetry. A plan for improvements has been laid out in all areas, but since they are all incremental, and each yielding potentially a few percent in polarization, development time and therefore the length of the run will be absolutely critical, as already mentioned, to bring these improvements into fruition.

It was very satisfactory in the session on Operations and Systems to review the significant progress we made in machine uptime and system reliability since last year, in result of a concerted effort to revert a worrisome downside trend in machine availability. Time at store increased from below 50% last run to almost 60% this run, a positive result reflected in reduced system failure hours and increased mean time between failures. Another factor in the increased availability has been the continued progress in minimizing the recovery time after scheduled maintenance, a direct result of better planning and use of resources. Areas of concerns remain, in particular the increase in human error in operations, errors spread among the operations staff, physicists, and support personnel alike. That was analyzed and discussed by the operations staff and remedial actions proposed, ranging from clarifications in procedures to requests of making operations software and systems less error prone. We reviewed plans and upgrades for all major systems to optimize the use of the likely long shutdown and with the goals to further improve system reliability. We also discussed possible multi-year and technically challenging system improvements, such as the compensation or correction of mechanical triplet vibrations, one of the limitations to RHIC ultimate performance.

As open discussion is one, if not the main goal of the Retreat itself we experimented this year for the first time with a full session devoted to organized discussion. A Panel of experts was assembled to collect and filter input from the entire RHIC community. Discussion topics were prioritized, divided in subject areas, and opened for discussion at the Retreat after a brief introduction by the proponent. The discussion was moderated by Panel Members and ultimately, when required, by the Chairman. Topics ranged from the technical to the organizational, and many will turn into action items after the Retreat. The outcome has been a very positive one, and it seems appropriate to repeat this experience at the future Retreats.

Finally the Retreat was summarized at the Closeout Session when we also had the opportunity of listening to the plan for commissioning and operating the LHC as an ion collider. The Retreat conclusions will be distributed in the form of a Retreat Summary document that will serve as a reference in the planning of next year operations.

As the Organizer I would like to take the opportunity of thanking all the participants for their excellent contributions, the Department for the support, and the Retreat Steering Committee and Panel Members for their invaluable advice in setting up the program of the Retreat.