V. Ptitsyn

RHIC pressure rise and electron cloud

In RHIC high intensity operation, two types of pressure rise are currently of concern. The first type is at the beam injection, which seems to be caused by the electron multipacting, and the second is the one at the beam transition, where the electron cloud is not the dominant cause. The first type of pressure rise is limiting the beam intensity and the second type might affect the experiments background for very high total beam intensity. In this article, the pressure rises at RHIC are described, and preliminary study results are reported. Some of the unsettled issues and questions are raised, and possible counter measures are discussed.

Measurement and correction of linear effects in the RHIC interaction regions

A considerable amount of betatron coupling in RHIC was found to originate from the interaction region (IR) triplets. A series of dedicated beam studies was performed with the goal of measuring the coupling errors in the IR triplets. The studies used two different methods: local interaction region orbit bumps and the action jump trajectory analysis. The availability of independently powered skew-quadrupole corrector elements in the triplets allow local, beam-based coupling correction in the RHIC interaction regions using the analysed beam data. We also discuss plans for linear IR correction in the RHIC year 2001 run.

Commissioning of RHIC deuteron-gold collisions

Deuteron and gold beams have been accelerated to a collision energy of /spl radic/s = 200 GeV/u in the Relativistic Heavy Ion Collider (RHIC), providing the first asymmetric-species collisions of this complex. Necessary changes for this mode of operation include new ramping software and asymmetric crossing angle geometries. This paper reviews machine performance, problems encountered and their solutions, and accomplishments during the 16 weeks of ramp-up and operations.

Observation of strong-strong and other beam-beam effects in RHIC

RHIC is currently the only hadron collider in which strong-strong beam-beam effects can be seen. For the first time, coherent beam-beam modes were observed in a bunched beam hadron collider. Other beam-beam effects in RHIC were observed in operation and in dedicated experiments with gold ions, deuterons and protons. Observations include measurements of beam-beam induced tune shifts, lifetime and emittance growth measurements with and without beam-beam interaction, and background rates as a function of tunes. During ramps unequal radio frequencies in the two rings cause the crossing points to move longitudinally. Thus bunches experience beam-beam interactions only in intervals and the tunes are modulated. In this article we summarize the most important beam-beam observations made so far.

RHIC beam instrumentation

AbstractRHICinstrumentationsystemsmustaccuratelycharacterizediversebeamsofupto110bunchesineachofthetwocolliderrings,rangingfrom10 11 protons/bunchat250GeVto10 9 Au þ79 ions/bunchat100GeV=nucleon; aswellaslower-intensitycommissioningandpilotbunches.Thecolliderinstrumentationincludes:667beampositionmonitor(BPM)channels,363beamlossmonitor(BLM)channels,wallcurrentmonitors,DCcurrenttransformers,ionizationprofilemonitors,tunemeasurementdevices,andresonantSchottkymonitors.ColliderinstrumentationisalsousedintheAGS-to-RHICtransferline,including52BPMchannels,56BLMchannels,5fastintegratingcurrenttransformers,and12videobeamprofilemonitors(RHICDesignManual,April1998;Proceedingsofthe’98BeamInstrumentationWorkshop,1998).PublishedbyElsevierScienceB.V. PACS: 29.20.Lq;29.27. a;07.05.HdKeywords: Accelerator;RHIC;Instrumentation;Positionmonitor;Lossmonitor;Currentmonitor;Luminositymonitor 1. Beampositionmonitors1.1. BPM assemblies and cablesThebeampositionmonitor(BPM)electrodeassembliesforthecolliderringandtheAGS-to-RHIC(AtR)lineshareacommonmechanicaldesign[1].AllAtRassembliesoperateatroomtemperature;mostcolliderassembliesoperateat4:2K: Eachassemblycontains23cmlong,3cmwide shorted striplines with a controlled 50Oimpedance.Largestriplinescoupleenoughpowertoallowaccuratemeasurementoflow-intensitypilotbunches.Theshorteddesignrequireselectro-nicswithlowreturnlosstolimitimpedance,butthestaticcryogenicthermalloadisreducedbyafactoroftwoovermoreexpensiveback-termi-nateddesigns.Mostoftheassembliescontaintwoopposingstriplines,andmeasureeitherhorizontalorverticalbeampositionatalocationwithcorrespondinglarge optical beta function. These single-planemonitorsaredesignatedType1ðID¼ 8cmÞ; acutawayviewofoneisshowninFig.1.Incriticalareasaroundtheinteractionregions,assemblieswithfourstriplinesareinstalled,allowingsimulta-neousmeasurementofbothhorizontalandver-ticalpositions.Tomatchexpectedbeamsizeand

Operations and Performance of RHIC as a Cu-Cu Collider

The 5thyear of RHIC operations, started in November 2004 and expected to last till June 2005, consists of a physics run with Cu-Cu collisions at 100 GeV/u followed by one with polarized protons (pp) at 100 GeV [1]. We will address here the overall performance of the RHIC complex used for the first time as a Cu-Cu collider, and compare it with previous operational experience with Au, PP and asymmetric d-Au collisions. We will also discuss operational improvements, such as a squeeze to 85cm in the high luminosity interaction regions from the design value of 1m, system improvements, machine performance and limitations, and address reliability and uptime issues.

Commissioning spin rotators in RHIC

During the summer of 2002, eight superconducting helical spin rotators were installed into RHIC in order to control the polarization directions independently at the STAR and PHENIX experiments. Without the rotators, the orientation of polarization at the interaction points would only be vertical. With four rotators around each of the two experiments, we can rotate either or both beams from vertical into the horizontal plane through the interaction region and then back to vertical on the other side. This allows independent control for each beam with vertical, longitudinal, or radial polarization at the experiment. In this paper, we present results from the first run using the new spin rotators at PHENIX.

Polarized Proton Acceleration in the AGS with Two Helical Partial Snakes

Acceleration of polarized protons in the energy range of 5 to 25 GeV is particularly difficult: the depolarizing resonances are strong enough to cause significant depolarization but full Siberian snakes cause intolerably large orbit excursions and are not feasible in the AGS since straight sections are too short. Recently, two helical partial snakes have been built and installed in the AGS. With careful setup of optics at injection and along the ramp, this combination can eliminate the intrinsic and imperfection depolarizing resonances encountered during acceleration. This paper presents the accelerator setup and preliminary results.

Spin dynamics in AGS and RHIC

A fundamental aspect of particle physics is the spin of the particles. With polarized beams, the internal structure of the proton may be probed in ways that are unattainable with unpolarized beams. The Relativistic Heavy Ion Collider (RHIC) has the unique capability of colliding protons with both transverse and longitudinal polarization at center-of-mass energies up to 500 GeV. In this paper we examine the methods used to accelerate and manipulate polarized proton beams in RHIC and its injectors. Special techniques include the use of a partial Siberian snake and an ac dipole in the AGS. In RHIC we use four superconducting helical Siberian snakes (two per ring) for acceleration, and eight superconducting helical rotators for independent control of polarization directions at two interaction regions.

Observation of Electron-Ion Effects at RHIC Transition

Electron cloud is found to be a serious obstacle on the upgrade path of the Relativistic Heavy Ion Collider (RHIC). At twice the design number of bunches, electron-ion interactions cause significant instability, emittance growth, and beam loss along with vacuum pressure rises when the beam is accelerated across the transition.