H. Hirabayashi

The Brookhaven muon storage ring magnet

Abstract The muon g-2 experiment at Brookhaven National Laboratory has the goal of determining the muon anomalous g-value a μ (=(g−2)/2) to the very high precision of 0.35 parts per million and thus requires a storage ring magnet with great stability and homogeniety. A superferric storage ring with a radius of 7.11 m and a magnetic field of 1.45 T has been constructed in which the field quality is largely determined by the iron, and the excitation is provided by superconducting coils operating at a current of 5200 A. The storage ring has been constructed with maximum attention to azimuthal symmetry and to tight mechanical tolerances and with many features to allow obtaining a homogenous magnetic field. The fabrication of the storage ring, its cryogenics and quench protection systems, and its initial testing and operation are described.

Development of superconducting magnets for beam lines and accelerator at KEK

Recent rapid development of superconducting magnets at KEK is reported. KEK is now constructing a superconducting pion beam line at the 12GeV Proton Synchrotron. A large bore superconducting dipole and a superconducting septum magnet for the beam line have been manufactured and successfully tested. Concurrently KEK is developing big aperture superconducting accelerator magnet of warm iron and warm bore. The first 1m model dipole of coil I.D. 14cm has been assembled and tested. A dipole field of 5.1 Tesla has been obtained in the second cool down test. This is a test dipole for TRISTAN proton ring magnet. Development program of superconducting magnets at KEK is also presented.

Detector magnets in high energy physics

The research developments concerning detector magnets for high-energy physics during 1985 to 1987 are briefly described. It is noted that after the 9th International Conference on Magnet Technology at Zurich in 1985, the major developments in this field have been made in colliding beam detectors in Europe, Japan and the US. The authors compare and discuss the CDF, TOPAZ, VENUS, AMY, ALEPH, DELPHI, and CLEO-II detectors. >

Design, fabrication, and test of a 5-cm aperture, 1-m long superconducting dipole prototype for high energy Hadron collider

A 1-m-long superconducting dipole prototype with an aperture of 5 cm and a rated field of 6.6 T was built and tested. This model was based on a two-layer cosine-theta coil clamped by stainless steel collars inside a laminated iron yoke, with a large keystone-angle cable and no wedge. The cold mass was encased in an outer stainless steel skin. The magnet was instrumented with voltage taps, which allow the location of the quench start, and with strain gauges, which allow the measurement of the coil stress variations during assembly, cool-down, and energization. Prior to the assembly, several tests were carried out in order to understand the mechanical properties of the coil and to determine a proper calibration for the strain gauges. A report is presented on the design studies, with emphasis on the calibration problem, followed by a discussion of the magnet assembly and quench performance in light of the mechanical measurements.

Interstrand coupling losses of Rutherford cables

Interstrand coupling losses of Rutherford cables are easily affected by curing conditions. We have measured the interstrand coupling losses and contact resistances for three kinds of Rutherford cable, made from strands with a Cu matrix, a CuMn barrier around a filamentary bundle and a CuMn matrix inside a Cu sheath. Furthermore we have observed the contact surfaces of the strands by using a scanning electron microscope. We have found that strands of cables with a Cu surface were bonded at crossover points cured at higher temperatures, and there were traces of diffusion bonding on the contact surfaces. We have also investigated the mechanical properties of the matrix materials and reviewed the fabrication process of magnets in which pressure is released after curing. We have concluded that the losses are determined by a balance between bonding forces and spring back of the strands.

Large aperture superconducting magnet (benkei)

Abstract Benkei, which was a large window frame conventional magnet at KEK has been converted to a superconducting magnet. In the conversion, the pole gap has been doubled from 0.5 m to 1.0 m retaining an analysing power at 2 T m. Several new techniques were applied to coil windings and cryostat fabrication. The superconducting Benkei has shown satisfactory performances for long term operation.

1.8 K test of binary and ternary superconducting conductors

A series of short sample tests have been carried out on Nb-Ti-based binary and ternary alloy conductors. It turns out that the current carrying capacities at high fields of both binary and ternary alloys can be remarkably improved over those previously reported by heavy cold-working after heat treatment. It should be emphasized that the superconducting performance of these ternary alloy conductors manufactured in industrial scale are fairly reliable and that the best results are obtained with Nb-Ti-Ta ternary alloys. Results are shown also on long samples and large kiloampere cables.

Design study of a superconducting dipole model magnet for the Large Hadron Collider

A design study of a high-field superconducting dipole magnet for the LHC (Large Hadron Collider) project has been carried out in cooperation between CERN and KEK. The objective is to develop a 1-m twin-aperture dipole model magnet based on double shell coil design with a fully symmetric split collaring structure. Development of superconducting cable with high keystone angle is a key technology to realize this magnet. The progress made in the design study and the development of the 1-m dipole model magnet are described.

A 3 T superconducting magnet for the amy detector

Abstract A 3 T high field superconducting magnet was constructed for the AMY detector at the TRISTAN electron-positron storage ring. Cooldown and excitation tests of the magnet were carried out with the detector in its final configuration. The coil is made with a fully stabilized superconductor wound into an eight layer cylinder with a 2.39 m inner diameter, a 2.58 m outer diameter and 1.54 m in length. An outer jacket of thick stainless steel was shrunk-fit around the coil to provide strength to contain the magnetic forces and to serve as a liquid helium container for the pool boiling cooling system for the coil. A computer controlled refrigeration system with a capacity of 300 W at 4.4. K (100 l/h) was prepared to cool down the 17 t of cold mass of the magnet. It took about five days to cool down from room temperature and achieve a superconducting state, and an additional two days to completely fill the coil with liquid helium and to prepare for the excitation of the magnet. The thermal stresses on the coil support rods were evenly balanced during the cooldown, and the mechanical stresses on the support rods at full excitation (a current of 5000 A) were well below the allowed maximum. In order to verify the safe operation of the magnet system, we carried out fast discharge tests with a time constant of 21 s, which was optimized to protect the magnet from quench. The pressure rise in the helium vessel during the discharge from 5000 A was an easily manageable 1.38 × 10 5 Pa. During the fast discharge of the 5000 A excitation, the coil showed no signs of developing any normal regions. At the maximum rated current of 5000 A, the central magnetic field and the inductance were measured to be 3.0367 and 3.2 H, respectively, corresponding to a stored energy of 40 MJ, in good agreement with magnetic field calculations. During these tests and in the succeeding long term operation, the magnet showed excellent stability and reliability.

Spallation of niobium by 12 GeV protons

Abstract Cross sections for the production of approximately 50 radionuclides in the interaction of niobium with 12 GeV protons were determined by the activation technique. The results were parametrized in terms of a 6-parameter equation which reproduced the measured charge-dispersion and mass-yield curves.