P. Cameron

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.

Electron Cooling of RHIC

We report progress on the R&D program for electron-cooling of the Relativistic Heavy Ion Collider (RHIC). This electron cooler is designed to cool 100 GeV/nucleon at storage energy using 54 MeV electrons. The electron source will be a superconducting RF photocathode gun. The accelerator will be a superconducting energy recovery linac. The frequency of the accelerator is set at 703.75 MHz. The maximum electron bunch frequency is 9.38 MHz, with bunch charge of 20 nC. The R&D program has the following components: The photoinjector and its photocathode, the superconducting linac cavity, start-to-end beam dynamics with magnetized electrons, electron cooling calculations including benchmarking experiments and development of a large superconducting solenoid. The photoinjector and linac cavity are being incorporated into an energy recovery linac aimed at demonstrating ampere class current at about 20 MeV.

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.

RHIC beam position monitor assemblies

Design calculations, design details, and fabrication techniques for the RHIC BPM Assemblies are discussed. The 69 mm aperture single plane detectors are 23 cm long short-circuited 50 ohm strip transmission lines subtending 80 degrees. They are mounted on the sextupole end of the corrector-quadrupole-sextupole package and operate at liquid helium temperature. The 69 cm aperture was selected to be the same as that of the beampipe in the CQS package, the 23 cm length is a compromise between mechanical stability and electrical sensitivity to the long low-intensity proton and heavy ion bunches to be found in RHIC during commissioning, and the 80 degree subtended angle maximizes linear aperture. The striplines are aligned after brazing to maintain electrical-to-mechanical centers within 0.1 mm radius, eliminating the need for individual calibration. Because the cryogenic feedthrus isolate the UHV beam vacuum only from the HV insulating vacuum, and do not see liquid helium, a replaceable mini-ConFlat design was chosen to simplify fabrication, calibration, and maintenance.<<ETX>>

Transverse instabilities in RHIC

The beam quality in RHIC can be significantly impacted by a transverse instability which can occur just after transition. Data characterizing the instability are presented and analyzed. Techniques for ameliorating the situation are considered.

Spallation Neutron Source beam loss monitor system

The Spallation Neutron Source (SNS) being built at Oak Ridge National Laboratory (ORNL) is designed to deliver 1.5/spl times/10/sup 14/ protons at 1.0 GeV in one bunch at 60 Hz to a liquid mercury target. To achieve this without excessive activation, an uncontrolled loss criteria of 1 part in 10/sup 4/ (/spl sim/1 W/m) has been specified. Measured losses will provide machine tuning data, a beam abort trigger, and logging of loss history. The design of the distributed loss monitor system utilizing argon-filled ionization chambers and photomultipliers will be presented, as well as data from tests with beam.

RHIC transverse injection damping

Since the beginning of the currently ongoing RHIC run a transverse injection damper is available. The damper is based on a fast kicker module in combination with a HV power supply and fast HV switches. This system can damp one injected bunch at the time with a given kick amplitude (bang-bang mode) for several hundred turns. This report gives an overview of the injection damping system and summarizes its performance and our experience during the first months of usage.

Spallation Neutron Source ring diagnostics

Brookhaven is providing the Ring and Transfer Lines Beam Diagnostics for the Spallation Neutron Source (SNS), to be installed at Oak Ridge National Laboratory. The customary diagnostics that will be present include beam position monitors (BPM), ionization profile monitors (IPM), beam loss monitors (BLM), beam current monitors (BCM), coherent tune measurement, and wire scanners. An overview of these systems is presented, along with brief discussions of SNS-specific problems that must be addressed, including unprecedented beam power, large dynamic range, a stringent loss budget, space charge, beam halo, and electron cloud. We also present an overview of systems more specifically tailored to address these problems, including Beam-in-Gap measurement and cleaning, two types of incoherent tune measurement, halo monitor, and video monitors for stripping foils and the electron catcher.

Spallation neutron source beam loss monitor system

The Spallation Neutron Source facility to be built at ORNL is designed to accumulate 2×1014 protons at 1.0 GeV and deliver them to the experimental target in one bunch at 60 Hz. To achieve this goal and protect the machine from excessive radiation activation, an uncontrolled loss criteria of 1 part in 104u200a(1u200aW/m) has been specified. Measured losses will be conditioned to provide machine tuning data, a beam abort trigger, and logging of loss history. The design of the distributed loss monitor system utilizing argon-filled glass ionization chambers and scintillator-photomultipliers will be presented.