S.Y. Zhang

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.

Accumulator ring design for the NSNS project

The goal of the proposed National Spallation Neutron Source (NSNS) is to provide a short pulse proton beam of about 0.5 /spl mu/s with average beam power of 1 MW. To achieve such purpose, a proton storage ring operated at 60 Hz with 1/spl times/10/sup 14/ protons per pulse at 1 GeV is required. The Accumulator Ring (AR) receives 1 msec long H/sup -/ beam bunches of 28 mA from a 1 GeV linac. Scope and design performance goals of the AR are presented, other possible technological choices and design options considered, but not adopted, are also briefly reviewed.

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.

Electron cloud observations and cures in RHIC

Since 2001 RHIC has experienced electron cloud effects, which have limited the beam intensity. These include dynamic pressure rises - including pressure instabilities, tune shifts, a reduction of the stability threshold for bunches crossing the transition energy, and possibly incoherent emittance growth. We summarize the main observations in operation and dedicated experiments, as well as countermeasures including baking, NEG coated warm beam pipes, solenoids, bunch patterns, anti-grazing rings, pre-pumped cold beam pipes, scrubbing, and operation with long bunches. This article is a short version of [1].

Accelerating polarized protons to 250 GeV

The relativistic heavy ion collider (RHIC) as the first high energy polarized proton collider was designed to provide polarized proton collisions at a maximum beam energy of 250 GeV. It has been providing collisions at a beam energy of 100 GeV since 2001. Equipped with two full Siberian snakes in each ring, polarization is preserved during the acceleration from injection to 100 GeV with careful control of the betatron tunes and the vertical orbit distortions. However, the intrinsic spin resonances beyond 100 GeV are about a factor of two stronger than those below 100 GeV making it important to examine the impact of these strong intrinsic spin resonances on polarization survival and the tolerance for vertical orbit distortions. Polarized protons were accelerated to the record energy of 250 GeV in RHIC with a polarization of 46% measured at top energy in 2006. The polarization measurement as a function of beam energy also shows some polarization loss around 136 GeV, the first strong intrinsic resonance above 100 GeV. This paper presents the results and discusses the sensitivity of the polarization survival to orbit distortions.

Electron-cloud mitigation in the Spallation Neutron Source ring

The Spallation Neutron Source (SNS) accumulator ring is designed to accumulate, via H/sup -/ injection, protons of 2 MW beam power at 1 GeV kinetic energy at a repetition rate of 60 Hz. At such beam intensity, electron-cloud is expected to be one of the intensity-limiting mechanisms that complicate ring operations. This paper summarizes mitigation strategy adopted in the design, both in suppressing electron-cloud formation and in enhancing Landau damping, including tapered magnetic field and monitoring system for the collection of stripped electrons at injection, TiN coated beam chamber for suppression of the secondary yield, clearing electrodes dedicated for the injection region and parasitic on BPMs around the ring, solenoid windings in the collimation region, and planning of vacuum systems for beam scrubbing upon operation.

RHIC electron detector signal processing design

The RHIC gold beam intensity is presently limited by pressure rise at some warm sections, and the main cause is thought to be the electron cloud. For the FY2003 RHIC run, a system has been installed to characterize the electron cloud, if it exists. The system is comprised of electron detectors, high voltage bias supplies, signal amplifiers, and data acquisition electronics, all integrated into the control system. The 11 detectors are grouped into four locations, one in an interaction region and three in single beam straight sections. This paper describes the signal processing design of the detector system, and includes data collected from the FY2003 run.

The RHIC injector accelerator configurations, and performance for the RHIC 2003 Au-d Physics Run

The RHIC 2003 Physics Run required collisions between gold ions and deuterons. The injector necessarily had to deliver adequate quality (transverse and longitudinal emittance) and quantity of both species. For gold this was a continuing evolution from past work. For deuterons it was new territory. For the filling of the RHIC the injector not only had to deliver quality beams but also had to switch between these species quickly. This paper details the collider requirements and our success in meeting these. Some details of the configurations employed are given.

Accelerating Polarized Protons to High Energy

The Relativistic Heavy Ion Collider (RHIC) is designed to provide collisions of high energy polarized protons for the quest of understanding the proton spin structure. Polarized proton collisions at a beam energy of 100 GeV have been achieved in RHIC since 2001. Recently, polarized proton beam was accelerated to 250 GeV in RHIC for the first time. Unlike accelerating unpolarized protons, the challenge for achieving high energy polarized protons is to fight the various mechanisms in an accelerator that can lead to partial or total polarization loss due to the interaction of the spin vector with the magnetic fields. We report on the progress of the RHIC polarized proton program. We also present the strategies of how to preserve the polarization through the entire acceleration chain, i.e. a 200 MeV linear accelerator, the Booster, the AGS and RHIC.

RHIC Performance with Polarized Protons in Run-6

The RHIC polarized proton run (Run‐6) in 2006 started on February 1 and continued for 21 weeks. The Run‐6 included the machine operation at different beam energies and with different orientation of beam polarization at the collision points. The machine operation at 100GeV and 31.2 GeV provided physics data of polarized proton collisions to the STAR, PHENIX and BRAHMS experiments. Record levels of the luminosity (up to 3.5⋅1031 cm−2 s−1 peak) and proton beam polarization (up to 65%) were achieved during the 100GeV operation. The beam polarization was preserved during the acceleration by using Siberian Snakes, based on helical magnets. The polarization orientation at STAR and PHENIX experiments was controlled with helical spin rotators. During different stages of the run the physics data were provided with longitudinal, vertical and horizontal orientations of the beam polarization at the collision points. Total luminosity integrals of 45 pb−1 at 100 GeV and 0.35 pb−1 at 31.2 GeV were delivered to the experi...