The Relativistic Heavy Ion Collider (RHIC) completed its fifth year of operation in 2005, colliding copper ion beams with ps=200 GeV/u and 62.4 GeV/u[1]. Previous heavy ion runs have collided gold ions at ps=130 GeV/u, 200 GeV/u, and 62.4 GeV/u[2], and deuterons and gold ions at ps=200 GeV/u[3]. This paper discusses operational performance statistics of this facility, including Cu- Cu delivered luminosity, availability, calendar time spent in physics stores, and time between physics stores. We summarize the major factors affecting operations efficiency, and characterize machine activities between physics stores

Calaga, R

Ferrone, R

Pilat, F

Satogata, T

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RHIC HEAVY ION OPERATIONS PERFORMANCE∗T. Satogata,† , R. Calaga, K. Ferrone, F. Pilat, BNL, Upton, NYAbstractThe Relativistic Heavy Ion Collider (RHIC) completedits fifth year of operation in 2005, colliding copper ionbeams with√s=200 GeV/u and 62.4 GeV/u[1]. Previousheavy ion runs have collided gold ions at√s=130 GeV/u,200 GeV/u, and 62.4 GeV/u[2], and deuterons and goldions at√s=200 GeV/u[3]. This paper discusses opera-tional performance statistics of this facility, including Cu-Cu delivered luminosity, availability, calendar time spent inphysics stores, and time between physics stores. We sum-marize the major factors affecting operations efficiency,and characterize machine activities between physics stores.1. INTRODUCTIONRHIC consists of two independent superconducting3.8 km rings (the “blue” and “yellow” rings), intersect-ing at six interaction points (IPs) and providing luminosityto 2–4 concurrent experiments. RHIC has completed fivesuccessful physics runs since commissioning in 1999, in-cluding both heavy-ion and polarized proton spin physicsprograms. Table 1 shows design, achieved, and upgrademachine parameters for RHIC as an ion collider.Figure 1 summarizes RHIC performance in the 2005 Cu-Cu√s=200 GeV/u run. Measured luminosity at four ex-periments is compared to minimum and maximum lumi-nosity projections from run planning documents[4], withminimum projections based on previous RHIC heavy-ion.RHIC as a Cu-Cu collider exceeded the maximum pro-jection, achieving 15 nb−1 of integrated luminosity atthe low-β? experiments, more than twice the 7nb−1goal.The initial physics production store of 28 bunches of4.5×109evolved into the final configuration of 37 bunches∗Work performed under Contract Number DE-AC02-98CH10886 withthe auspices of the US Department of Energy.† Author email address: satogata@bnl.govFigure 1: Delivered Cu-Cu√s=200 GeV/u luminosity inRHIC Run-5.with 5×109Cu ions/bunch.With ions, injection is performed with β?=10 m at allIPs, and acceleration ramps squeeze to β?=5 m at all IPsto optimize for transition jump optics. β? is then squeezedto final collision optics during the remainder of the accel-eration ramp to minimize ramping time to reach collisionoptics. Collision optics are typically set to β?=5 m at non-experimental IPs, and β?=0.85–3 m at experimental IPs.These settings are based on experiment background issuesand presence of nonlinear correctors. The beams are ver-tically separated with ±5 mm bumps through the acceler-ation ramp, and RF-locked in an “anti-cogged” position toavoid detrimental beam-beam effects.A change of species for a RHIC run typically requiresabout 1–3 weeks of setup period to establish ramping andcollisions. This is followed by 1–2 weeks of ramp-up to setup detectors and maximize luminosity production. This isa substantial portion of the typical 27–31 weeks of annualRHIC operations. Setup and ramp-up periods are shorterduring planned mid-run species changes, as injector devel-opment can often occur during RHIC physics stores.2. THE RHIC CYCLEFig. 2 shows activity in RHIC between two Cu-Cuphysics stores in 2005. The details shown are typical forthe periods between same-species heavy-ion physics storesat RHIC, and can be divided into four periods: beam dumpand magnet ramping, preparing beam for injection, accel-erating beam to collision energy, and preparing collisionsfor physics. The period from dumping beams to the start ofphysics data collection is defined as turn-around time, andis discussed in the next section. All times in the followingparagraphs refer to Fig. 2.From 18:12:30 to 18:18:00, beams are dumped, andRHIC magnets are ramped down to a parking current andback to injection to maintain proper hysteresis. This time isdominated by limits set by superconducting magnet quenchdetection. The beam dump time was originally determinedby a voting consensus among participating experiments;physics stores are now a fixed length, optimized to max-imize usable luminosity delivered to experiments.From 8:18:00 to 8:33:00, beams are prepared for in-jection. This period is highly variable, depending on theinjector readiness and the amount of injection tuning re-quired. Injector readiness also benefits from fixed physicsstore lengths, as dump times are more predictable for op-erations when running multiple injector physics programsand saving energy costs. Pulsed injector element drift andpersistent current chromatic effects (drifting about 2 unitsover 15 minutes after returning to injection[5]) are the mainLHC-LUMI-05 PROCEEDINGS127Table 1: RHIC 200 GeV/u heavy c.m. energy ion performance evolution. Run-# parameters shown provided the highestexperiment luminosities. Enhanced luminosity numbers are facility goals c. 2008, before electron cooling.Species [Run] No of Ions/bunch β? Emittance Lpeak Lstore,ave Lweekbunches [109] [m] [piµrad] [×1026 cm−2s−1]Au-Au (Design) 56 1.0 2 15-40 9 2 50 µb−1d-Au (Run-3) 55/110 120d/0.7Au 2 15 700 200 4.5 nb−1Au-Au (Run-4) 45 1.1 1 15-40 15 4 160 µb−1Cu-Cu (Run-5) 36 4.5 0.85 10–30 198 80 2.3 nb−1Au-Au (Enhanced) 112 1.1 1 15-40 36 9 350 µb−1items requiring further injection tuning in this period. Atthe end of this period, both rings are filled with fresh beamand ready for acceleration. The bottom plot of Fig. 2 showsFrom 8:33:00 to 8:38:00, beams are accelerated to colli-sion energy. The top plot shows the main magnets rampingback up to storage energy, while the bottom plot shows agroup of vertical red lines marking tuning points throughthe acceleration ramp. RHIC is the only superconductingaccelerator to cross transition, and beam intensity lossesare seen before and through transition. The heavy ion ac-celeration ramp time of about five minutes is dominated bylimits set by superconducting magnet quench detection.From 8:38:00 to 8:40:00 collisions are prepared forphysics. This includes longitudinal RF cogging, rebuck-eting into 198 MHz RF storage cavities, collision steering,and collimation setup. The preparation time for physicscollisions can be as long as tens of minutes with collisionFigure 2: Activity in RHIC between two Cu-Cu stores. Thebottom plot shows beam current. The top plot shows mea-sured experiment luminosity and main dipole current. SeeSection 2 for further details.optimization at all four IPs, and collimation optimization tominimize backgrounds. This is often necessary when push-ing machine parameters to maximize delivered luminosity.Upon completion of these items, an event (ev-physics) isgenerated to notify all experiments that machine setup forthat physics store is complete.With the exception of injection tuning and some aspectsof physics setup (collision steering, collimation), all activi-ties between stores are controlled by a software sequencer.This program ensures store-to-store reproducibility of ma-chine activities, and automatically checks for error condi-tions such as premature abort kicker slow discharge or un-expected beam loss.3. TIME BETWEEN STORESThe time between dumping beams and the next physicsdata collection start is defined as turn-around time. Heavyion luminosity degradation during a physics store is domi-nated by intrabeam scattering, naturally leading to a shortstore lengths and more turn-around times. Therefore, itis crucial to charaterize every step in the turn-around timeprocess and minimize it, since heavy ion luminosity degra-dation during physics stores due to intrabeam scatteringnaturally leads to shorter store lengths and more frequentstore turn-around. Fig. 3 shows the turn-around time for allstores during the RHIC Cu-Cu√s=200 GeV/u run. Theaverage time between stores in this pariod was 75 minuteswithout including extremely long failure times of greaterthan ten hours.Figure 3: Histogram of turn-around time for the RHIC Cu-Cu√s=200 GeV/u run.LHC-LUMI-05 PROCEEDINGS128The turn-around times in Fig. 3 fall into three categories:routine, excessive, and failure. 80% of turn-around timesshown were routine, 10% were excessive, and 10% werefailure. Section 2 shows described one example of a rou-tinely achieved turn-around time of about 25 minutes. In-tegrated luminosity gains of 5–10% can be achieved by re-ducing the average turn-around time to 25 minutes. Turn-around times of less than 120–130 minutes are consideredroutine, and are usually longer than the optimal turn-aroundtime because of injector readiness problems, or experimentaccess between stores for minor equipment repair.Moderately long turn-around times (120–300 minutes)can be attributed to aggressive machine development, su-perconducting magnet quench link interlocks, or significantequipment repair, such as power supply replacement. Withonly eight weeks available for high-energy Cu-Cu physicsoperation, incremental luminosity development was neces-sary, including gradual increase in beam intensity and num-ber of bunches. This development occasionally resulted ina store abort from pressure rise or beam losses.Excessively long turn-around times (longer than 300minutes) were all associated with facility failures. Thesefailures include two blizzards, experiment or acceleratorfailures that were spontaneously converted into mainte-nance days, and power dips.4. RELIABILITY AND UPTIMEFig. 4 shows the percentage of calendar time spentin store conditions for over the past four years. Thetime in store for the past two years has been about 52-53%. The overall goal is 60% calendar time in store (101hours/week). The time in store is measured from the eachev-physics on event to the corresponding beam dump event.Calendar time, including scheduled maintenance and ac-celerator physics experiments, is used to calculate the frac-tional time in store. Each experiment uses this time differ-ently depending on detector readiness and turn-on time.Time in collisions at store for the Cu-Cu√s=200 GeV/urun was 52% of calendar time, and increased to 74% ofcalendar time for the√s=62.4 GeV/u run. The significantFigure 4: RHIC calendar time spent at storage energy foreach run.Figure 5: RHIC 2005 Cu-Cu run availability by week.difference in uptime for the two operational modes can beattributed to an increased quench margin and to the morerelaxed beam parameters used for the low energy run, in-cluding 30% lower bunch intensity and a larger β? at thelow-β? interactions. The facility availability of the ma-chine for all uses including physics stores, setup, ramp-ing, and beam experiments is shown in Fig. 5. The averageavailability was near the target value of 80%.Future RHIC luminosity upgrades involve electron cool-ing of the ion beams. R&D of a 54 MeV electron cooleris underway, with expected completion in 2008. A weeklyintegrated Au-Au luminosity of 350 µbarns is planned be-fore the cooling upgrade, as shown Table 1. Injectors areproviding design intensity. Efforts are concentrating on in-creasing the number of bunches colliding per physics fill,currently limited by electron cloud and pressure rise ef-fects. Facility physics time of 60% and availability of 80%will be maintained with efforts to automate and speed upcollimation, collision steering, and other factors affectingturn-around time.ACKNOWLEDGEMENTSThe authors thank W. Fischer, P. Ingrassia, and T. Roserfor supporting information and helpful comments.REFERENCES[1] F. Pilat et al., “Operations and Performance of RHIC as a Cu-Cu Collider”, PAC’05, Knoxville, Tennessee (2005).[2] W. Fischer et al., “Luminosity Increases in Gold-Gold Oper-ation in RHIC”, proceedings of the 2004 European ParticleAccelerator Conference, Lucerne, Switzerland (2004).[3] T. Satogata et al., “Commissioning of RHIC Deuteron-GoldCollisions”, proceedings of the 2003 Particle AcceleratorConference, Portland, Oregon (2003).[4] T. Roser, W. Fischer, M. Bai, and F. Pilat, “RHICcollider projections: FY2005-2008”, available online athttp://www.rhichome.bnl.gov/RHIC/Runs/RhicProjections .[5] W. Fischer, A. Jain, and S. Tepikian, “Beam-based measure-ments of persistent current decay in the Relativistic HeavyIon Collider”, Phys. Rev. ST Accel. Beams 4, 041002 (2001).LHC-LUMI-05 PROCEEDINGS129

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