G. McIntyre

High Current Energy Recovery Linac at BNL

We present the design and parameters of an energy recovery linac (ERL) facility, which is under construction in the Collider-Accelerator Department at BNL. This R&D facility has the goal of demonstrating CW operation of an ERL with an average beam current in the range of 0.1 - 1 ampere and with very high efficiency of energy recovery. The possibility of a future upgrade to a two-pass ERL is also being considered. The heart of the facility is a 5-cell 703.75 MHz super-conducting RF linac with strong Higher Order Mode (HOM) damping. The flexible lattice of the ERL provides a test-bed for exploring issues of transverse and longitudinal instabilities and diagnostics of intense CW electron beams. This ERL is also perfectly suited for a far-IR FEL. We present the status and plans for construction and commissioning of this facility.

Extremely High Current, High-Brightness Energy Recovery Linac

Next generation light-sources, electron coolers, high-power FELs, Compton X-ray sources and many other accelerators were made possible by the emerging technology of high-power, high-brightness electron beams. In order to get the anticipated performance level of ampere-class currents, many technological barriers are yet to be broken. BNL’s Collider-Accelerator Department is pursuing some of these technologies for its electron cooling of RHIC application, as well as a possible future electron-hadron collider. We will describe work on CW, high-current and high-brightness electron beams. This will include a description of a superconducting, laser-photocathode RF gun and an accelerator cavity capable of producing low emittance (about 1 micron rms normalized) one nano-Coulomb bunches at currents of the order of one ampere average.

R&D towards cooling of the RHIC collider

We introduce the R&D program for electron-cooling of the Relativistic Heavy Ion Collider (RHIC). This electron cooler is designed to cool 100 GeV/nucleon bunched-beam ion collider at storage energy using 54 MeV electrons. The electron source will be an 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 bunch frequency is 28.15 MHz, with bunch charge of 10 nC. The R&D program has the following components: The photoinjector, the superconducting linac, start-to-end beam dynamics with magnetized electrons, electron cooling calculations and development of a large superconducting solenoid.

Metal and elastomer seal tests for accelerator applications

Abstract In excess of a thousand metal vacuum seals are used in the vacuum system of the Alternating Gradient Synchrotron (AGS) at Brookhaven National Laboratory. Numerous elastomer seals are used throughout the AGS to seal large beam component chambers. An accelerator upgrade program is being implemented to reduce the AGS operating pressure by a factor of 100 and improve the reliability of the vacuum system. This paper describes work in progress on metal and elastomer vacuum seals to help meet these two objectives. Tests are reported on the sealing properties of a variety of metal seals used with different sealing surfaces. Results are also given on reversible sorption properties of certain elastomers.

New results from crystal collimation at RHIC

In this paper, we discuss new results from the use of the crystal collimator from the 2003 run. The yellow ring of the Relativistic Heavy Ion Collider (RHIC) has a bent crystal collimator. By properly aligning the crystal to the beam halo, particles entering the crystal are deflected away from the beam and intercepted downstream in a copper scraper. The purpose of a bent crystal is to improve the collimation efficiency as compared to a scraper alone. We compare these results to previous data, simulation, and theoretical predictions.

Beam diffusion measurements at RHIC

During a store, particles from the beam core continually diffuse outwards into the halo through a variety of mechanisms. Understanding the diffusion rate as a function of particle amplitude can help discover which processes are important to halo growth. A collimator can be used to measure the amplitude growth rate as a function of the particle amplitude. In this paper we present results of diffusion measurements performed at the Relativistic Heavy Ion Collider (RHIC) with fully stripped gold ions, deuterons, and protons. We compare these results with measurements from previous years, and simulations, and discuss any factors that relate to beam growth in RHIC.

Design Considerations and Experience of the RHIC Dual Magnet Cryostat Installation

The first RHIC Dual Magnet installation, of eight (8) cold masses in one vacuum vessel, has been completed. Design of the system included the requirement for assembly on location, the need for individual three-direction alignment capability at each cold mass cradle, a fixed position cradle for the entire assembly, longitudinal slide capability for all other cradles, two thermally isolated heat shields, accessible electrical splice boxes, removable interconnects, removability of individual cold mass sections, flexible supply lines for electrical power and cryogenic services and external loads imposed from the supply services. Initially two of the twelve total assemblies were fabricated for the Sextant Test of the RHIC ring. This paper covers an overview of that effort from initial design considerations, fabrication/installation techniques, initial installation problems and the final design solutions.

Progress of 650 MHz SRF Cavity for eRHIC SRF Linac

A high-current, well-damped 5-cell 647 MHz cavity was designed for ERL-Ring based eRHIC. Two prototype cavities were contracted to RI Research Instruments GmbH: one copper cavity with detachable beampipes for HOM damping study, and one niobium cavity for performance study. The performance study includes high-Q study for ERL-Ring eRHIC design and high gradient study for Ring-Ring eRHIC design. This paper will present the preliminary results of the HOM study, progress on Nb cavity fabrication and preparation for vertical test.

Mechanical and thermal considerations for the superconducting magnet to normal conductor magnet warm-to-cold transitions of the RHIC accelerator

The RHIC accelerator, designed for maximum flexibility, allows for the insertion within the superconducting magnet lattice of specialty magnets of the normal conductor type. The beam character may then be customized at each of the experimental crossing points. This facility requires a beam tube transition from a cryogenic environment to ambient and back again. The “Warm-to-Cold Transition” is the system of mechanical and electrical components which permit this to occur. Discussed herein are: the systems mechanical degrees of freedom, shrinkage allowances, thermal and pressure induced stresses, cryogenic heat load, superconducting bus splices, and design considerations for each of the eight major assemblies.

Performance and Operating Experience of the RHIC First Sextant Test

Installation and testing of the first sextant of RHIC magnets has been completed. The tests consisted of temperature cycling, quenching magnets, and measuring important engineering parameters of a string of magnets totaling a length of over 500 meters. This represents one sixth of the 3.8 kilometer circumference of the RHIC machine and serves as a basis for extrapolation of parameters for full machine operation. This paper gives an overview of the entire system, a detailed discussion of startup problems, operations and cryogenic system reliability over the period of the test and details of some of the important cryogenic operating parameters.