M. Garber

Effect of Cu4Ti Compound Formation on the Characteristics of NbTi Accelerator Magnet Wire

High critical current density, Jc > 2500 A/mm2, and small filament diameter, d ¿ 3 ¿m, are required in multifilamentary NbTi wire used for superconducting accelerator magnets. Wires obtained from various commercial sources had Jcs in the range 1000 to 2800 A/mm2 and ds in the range 1 to 23 pm. The filaments were examined by means of scanning electron microscopy in order to determine the reason for the variation in Jc. It was found that the filaments in high Jc wires had clean smooth surfaces and uniform cross section along-their lengths. Filaments in low Jc wires show formation of Cu4Ti compound particles on their surfaces and large variations in cross section. The lower critical current measured in these wires is believed to be largely due to this effect. The superconducting-normal state transition is relatively wide in these wires.

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.

Critical Current Studies on Fine Filamentary NbTi Accelerator Wires

The magnets for the Superconducting Super Collider, a high energy proton colliding beam accelerator, require a superconductor with very high current density (> 2400 A/mm2at 5 T) and very small filaments (~ 2 μ m in diameter). Previous work has shown that by controlling the formation of Cu4Ti compound particles on the filament surfaces it is possible to make fine filamentary NbTi wire with high critical current density. The performance of multi-filamentary wire is characterized by the current density and the quantity “n” which describes the superconducting-normal transition. Micrographs of wires having high Jcand high n show smooth, uniform filaments. Recently wires of very high critical current and high n have been produced in experimental quantities by commercial manufacturers.

Superconducting Magnet System for RHIC

The proposed Relativistic Heavy Ion Collider1 (RHIC) will operate at ion energies of 7 to 100+ GeV/Amu for ions as heavy as Au197. This paper discusses the superconducting magnet system for this machine. It will consist of 372 dipoles typically 9.7 meters long with an operating field of 3.4 Tesla, 492 quadrupoles with typical length 1.4 meters, gradient 76 T/m, and approximately 1000 sextupole and corrector magnets. A detailed design has been developed for the dipoles which will have a clear bore of 76 mm; less detailed designs are presented for the other components. A proof-of-concept magnet has been constructed and successfully tested.

Performance of Four 4.5 M Two-in-One Superconducting R & D Dipoles for the SSC

Four 4.5 m long superconducting dipoles built to specifications similar to those for SSC Reference Design A have been successfully tested. They were wound with NbTi cable in two-layer cos¿ coils of 3.2 cm inner diameter. The coil ends were flared to increase thie minimum bending radius, anticipating coils wound from prereacted Nb3Sn. The coils were mounted in a reusable two-in-one iron yoke prestressed by means of a bolted stainless steel shell. The first two magnets as well as the fourth one, a special magnet designed to study cross-talk between the bores, used CBA/Tevatron cable. The third utilized cable with improved (high homogeneity) NbTi conductor. All four reached central fields corresponding to their short sample limits at 4.5K without training, nearly 6. OT for the first two magnets, 6.5T for the third, and 5.4T for the fourth. At 2.5K modest training was required to reach short sample limits of 7.2T, 7.1T, 7.8T, and 6.6T respectively. The measured values of the allowed harmonics were within several × 10-4 of the calculated ones.

Evaluation of SSC Cable Produced for the Model Dipole Program during 1989 and through February, 1990

During 1989 and the beginning of 1990, approximately 150,000 feet of cable was manufactured for use in the SSC Model Dipole Magnet Program. The wire for the cable was made to SSC specifications by three different manufacturers. The cable was made at New England Electric Wire on the SSC Production Cabling Machine, under supervision of either SSC Laboratory personnel or the wire manufacturer’s representative. All the cable produced for SSC model dipoles was subjected to rigorous inspection in order to insure that the magnet construction and performance would be predictable. The cable dimensions were measured at intervals of 10 feet or less with a cable measuring machine. Electrical properties were measured on samples from one end of each cable length. Critical current degradation due to cabling was checked by measuring the critical currents of the wires used to make the cable and comparing these with the cable critical current. The results of the dimensional and electrical measurements will be discussed and compared with the SSC specification requirements.

A 6.4 Tesla Dipole Magnet For the SSC

A design is presented for a dipole magnet suitable for the proposed SSC facility. Test results are given for model magnets of this design 1 m long and 4.5 m long. Flattened wedge-shaped cables (“keystoned”) are used in a graded, two-layer “cos θ” configuration with three wedges to provide sufficient field uniformity and mechanical rigidity. Stainless steel collars 15 mm in radial depth, fastened with rectangular keys, provide structural support, and there is a “cold” iron flux return. The outer-layer cable has 30 strands of 0.648 mm diameter NbTi multifilamentary wire with Cu/S.C. = 1.8, and the inner has 23 strands of 0.808 mm diameter wire with Cu/S.C. = 1.3. Performance data is given including training behavior, winding stresses, collar deformation, and field uniformity.

Status of magnet system for RHIC

Specifications for and the design of magnets for the relativistic heavy ion collider (RHIC) at the Brookhaven National Laboratory are discussed in this short talk.

Internal Trim Coils for CBA Superconducting Magnets

In order to correct iron saturation effects and shape the beam working line, superconducting trim coils have been constructed, which operate inside the main coils. Detailed studies of mechanical properties, quench behaviour, fields produced and hysteresis have lead to the production of accelerator quality coils generating the required strength harmonics up to cos (7¿). These are routinely installed in CBA main magnets and operate at 80% of short sample with negligible training in an ambient field of more than 5.3T.

Quench Propagation and Training in Simulated Superconducting Magnet Windings

Training behavior similar to that which occurs in full scale superconducting accelerator magnets has been observed in small test windings. The test coils are formed from approximately 20 meters of conductor wound non-inductively, in Bifilar fashion. The resulting racetrack shaped coil is molded at elevated temperature to simulate the construction techniques used for the ISABELLE dipoles. The quench current of such windings has been measured as a function of applied field and the effect of parameters such as mechanical loading and porosity have been investigated. The velocity of propagation of the normal front has been measured both along and transverse to the direction of current flow for several test windings. The minimum energy required to produce a self propagating normal zone has also been determined in an attempt to quantify the relative stability of the coils.