E. Willen

Polarized proton collider at RHIC

Abstract In addition to heavy ion collisions (RHIC Design Manual, Brookhaven National Laboratory), RHIC will also collide intense beams of polarized protons (I. Alekseev, et al., Design Manual Polarized Proton Collider at RHIC, Brookhaven National Laboratory, 1998 [2]), reaching transverse energies where the protons scatter as beams of polarized quarks and gluons. The study of high energy polarized protons beams has been a long term part of the program at BNL with the development of polarized beams in the Booster and AGS rings for fixed target experiments. We have extended this capability to the RHIC machine. In this paper we describe the design and methods for achieving collisions of both longitudinal and transverse polarized protons in RHIC at energies up to s =500 GeV .

About the mechanics of SSC dipole magnet prototypes

During the last two years, nine 4‐cm aperture, 17‐m‐long dipole magnet prototypes were produced by Brookhaven National Laboratory (BNL) under contact with the Superconducting Super Collider (SSC) Laboratory. These prototypes are the last phase of a half‐decade‐long R&D program, carried out in collaboration with Fermi National Accelerator Laboratory and Lawrence Berkeley Laboratory, and aimed at demonstrating the feasibility of the SSC main‐ring dipole magnets. They also lay the groundwork for the 5‐cm‐aperture dipole magnet program now underway. After reviewing the design features of the BNL 4‐cm‐aperture, 17‐m‐long dipole magnets, we describe in detail the various steps of their fabrication. For each step, we discuss the paramaters that need to be mastered, and we compare the values that were achieved for the nine most recent prototypes. The data appear coherent and reproducible, demonstrating that the assembly process is under control. We then analyze the mechanical behavior of these magnets during cool...

The RHIC design overview

The salient performance objectives for the Relativistic Heavy Ion Collider (RHIC) are presented and the rationale for the design choices of the major collider systems is conveyed. RHIC provides collisions of heavy ions covering the entire mass range from protons to gold. For the prototypical case of Au-on-Au, one obtains energies up to 100 GeV/n per beam and luminosities of B2 � 10 26 cm � 2 s � 1 , averaged over a 10-h storage time. Operation with polarized protons is also possible. The overall accelerator complex used for gold ions consists of the Tandem Van de Graaff, the Booster, the AGS, and the Collider itself, and the scenario for the beam transfer between machines is described. The two separate collider rings cross at six interaction points, where the lattice design provides low-beta insertions for maximum luminosity. The interaction diamond length of o20 cm rms is achieved by bunched beam operation and holding the 56 bunches in a 197 MHz radio-frequency (RF) system after their acceleration in a 28 MHz RF system. The rings are constructed with superconducting magnets, which have a cold bore aperture of 6.9 cm in the arcs. The RHIC specific design challenges posed by intrabeam scattering of heavy ions, passage through transition energy with slow-ramping superconducting magnets, and control of magnetic errors in the low-beta triplet quadrupoles are addressed. r 2002 Elsevier Science B.V. All rights reserved.

Tuning shims for high field quality in superconducting magnets

A high field quality in quadrupoles for the interaction region is crucial to the luminosity performance of high energy colliders such as the Relativistic Heavy Ion Collider (RHIC). The field quality in magnets is limited in part by manufacturing tolerances in the parts and assembly. A tuning shim method has been developed to reduce the relative field errors (/spl Delta/B/B) from /spl sim/10/sup -4/ to /spl sim/10/sup -5/ at 2/3 of the coil radius. Eight tuning shims having a variable thickness of iron are inserted after the construction and measurement of field harmonics in the magnet. In this paper the tuning shim technique is described for RHIC interaction region quadrupoles. The results of calculations and measurement are also presented.

A high field hts solenoid for muon cooling

The ability of high temperature superconducting (HTS) conductor to carry high currents at low temperatures makes feasible the development of very high field magnets for uses in accelerators and beam-lines. A specific application of a very high field solenoid is to provide a very small beta region for the final cooling stages for a muon collider. Since ionization cooling in a solenoid acts simultaneously on both transverse planes, any improvement in maximum field has a quadratic consequence in the reduction of the 6-dimensional (6D) beam emittance. This paper describes a conceptual design of a 45 Tesla solenoid based on Bi-2223 HTS tape, where the magnet will be operated at 4.2 K to take advantage of the high current carrying capacity at that temperature. In this design, an outer Nb3Sn shell surrounds the HTS solenoid. This paper describes the technical issues associated with building this magnet. In particular it addresses how to mitigate the large Lorentz stresses associated with the high field magnet and how to design the magnet to reduce the compressive end forces. Also this paper discusses the important issue of how to protect this magnet if a quench should occur.

Tests of full scale SSC R&D dipole magnets

Four full-scale SSC (Superconducting Super Collider) research and development dipole magnets, incorporating successive mechanical design improvements, have been quench-tested. Three of the magnets are heavily instrumented with sensors to measure their mechanical behavior and verify the effectiveness of the mechanical improvements and with multiple voltage taps to locate the origin of quenches. The last two magnets of this series reach the SSC design operating field of 6.6 T in two or fewer quenches. Load cells and motion sensors show that in these two magnets the azimuthal clamping stress is higher at zero current and drops more slowly with excitation that in previous long magnets, and that the axial motion of the coil upon excitation has been greatly reduced. Quenches are found to originate preferentially in several locations, suggesting other design improvements. >

Quench Start Localization in Full-Length SSC R&D Dipoles

Full-length SSC R&D dipole magnets instrumented with four voltage taps on each turn of the inner quarter coils have been tested. These voltage taps enable (1) accurate location of the point at which the quenches start and (2) detailed studies of quench development in the coil. Attention here is focused on localizing the quench source. After recalling the basic mechanism of a quench (why it occurs and how it propagates), the method of quench origin analysis is described: the quench propagation velocity on the turn where the quench occurs is calculated, and the quench location is then verified by reiterating the analysis on the adjacent turns. Last, the velocity value, which appears to be higher than previously measured, is discussed.

Superconducting Magnets for the CBA Project

Abstract The superconducting magnets that were designed and tested for the BNL colliding beam accelerator are described, including dipoles, quadrupoles and trim coils. The dipoles had an effective length of 436 cm, a good field aperture of 8.8 cm diameter, and were designed for an operating field of 5.28 T in a temperature range between 2.6 K and 3.8 K (provided by supercritical helium). The quadrupoles had the same aperture, an effective length of 138.5 cm, and were designed to operate in series with the dipoles, with a gradient of 70.8 T/m. The dipoles incorporated internal sextupole, octupole, and decapole trim coil windings; the quadrupole trim coils consisted of dipole, quadrupole, and dodecapole windings. The design, construction, and performance (training, field quality, quench protection characteristics) of prototype magnets are discussed in considerable detail.

ACCELERATION OF POLARIZED BEAMS USING MULTIPLE STRONG PARTIAL SIBERIAN SNAKES

Acceleration of polarized protons in the energy range of 5 to 25 GeV is particularly difficult since depolarizing spin resonances are strong enough to cause significant depolarization but full Siberian snakes cause intolerably large orbit excursions. Using a 20 - 30 % partial Siberian snake both imperfection and intrinsic resonances can be overcome. Such a strong partial Siberian snake was designed for the Brookhaven AGS using a dual pitch helical superconducting dipole. Multiple strong partial snakes are also discussed for spin matching at beam injection and extraction.

Construction of cold mass assembly for full-length dipoles for the SSC accelerator

Four of the initial six 17m long demonstration dipole magnets for the proposed Superconducting Super Collider have been constructed, and the first one is now being tested. This paper describes the magnet design and construction of the cold mass assembly. The magnets are cold iron (and cold bore) 1-in-1 dipoles, wound with partially keystoned current density-graded high homogeneity NbTi cable in a two-layer \cos \theta coil of 40 mm inner diameter. The magnetic length is 16.6 m. The coil is prestressed by 15 mm wide stainless steel collars, and mounted in a circular, split iron yoke of 267 mm outer diameter, supported by a cylindrical yoke (and helium) containment vessel of stainless steel. The magnet bore tube assembly incorporates superconducting sextupole trim coils produced by an industrial, automatic process akin to printed circuit fabrication.