C. Goodzeit

Measurement of internal forces in superconducting accelerator magnets with strain gauge transducers

An improved method has been developed for the measurement of internal forces in superconducting accelerator magnets, in particular the comprehensive stresses in coils and the end restraint forces on the coils. The transducers have been designed to provide improved sensitivity to purely mechanical strain by using bending mode deflections for sensing the applied loads. Strain gauge resistance measurements are made with a new system that eliminates sources of errors due to spurious resistance changes in interconnecting wiring and solder joints. The design of the transducers and their measurement system is presented along with a discussion of the method of compensation for thermal and magnetic effects, methods of calibration with typical calibration data, and measured effects in actual magnets of the thermal stress changes from cool-down and the Lorentz forces during magnet excitation. >

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.

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.

Tests of prototype SSC magnets

Results are presented from tests of the third full-scale development dipole magnet for the Superconducting Super Collider (SSC) and from a retest of a 4.5-m model magnet of the same design mounted in an SSC cryostat. The 4.5-m magnet showed consistent quench performance between its original tests in boiling liquid helium in a vertical dewar and the current tests in forced-flow helium in a horizontal cryostat. Little or no retraining was observed over several thermal cycles. The full-length magnet required 12 quenches to train to its short-sample limit of 6800 A and displayed a reasonably stable quench plateau following training. Data are presented on quench behavior as a function of current and temperature, and on azimuthal and longitudinal loading of the coil by the support structure. >

Full length prototype SSC dipole test results

Results are presented from tests of the first full length prototype SSC dipole magnet. The cryogenic behavior of the magnet during a slow cooldown to 4.5K and a slow warmup to room temperature has been measured. Magnetic field quality was measured at currents up to 2000 A. Averaged over the body field all harmonics with the exception of b 2 and b 8 are at or within the tolerances specified by the SSC Central Design Group. (The values of b 2 and b 8 result from known design and construction defects which will be corrected in later magnets.) Using an NMR probe the average body field strength is measured to be 10.283 G/A with point to point variations on the order of one part in 1000. Data are presented on quench behavior of the magnet up to 3500 A (approximately 55% of full field) including longitudinal and transverse velocities for the first 250 msec of the quench.

Quench Characteristics of Full-Length SSC R&D Dipole Magnets

Several 17-meter-long SSC R&D dipole magnets, instrumented with numerous voltage taps on the inner quarter coils, have been tested. These magnets, protected with quench heaters, differed in mechanical details as well as in the cables used for the winding. The voltage taps enabled us to measure longitudinal and azimuthal quench propagation velocities. Summary plots of these velocities are presented showing that, even though the Fourier conduction model doesn’t apply, the mechanism of the quench is reproducible from magnet to magnet. Correlations are established between the velocities and the fraction of short sample. After showing that for currents higher than 5000 A the magnet is self-protected, we investigate the relation between the number of MIITs and the quench characteristics.

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.

Results of magnetic field measurements of 40 mm aperture 17-m long SSC model collider dipole magnets

Magnetic field measurements have been made on twelve 17-m-long, 40-mm-aperture R&D superconducting dipoles. Data on dipole field strength, multipole coefficients, and alignment have been obtained. The data indicate that the magnets as built are generally within the expectations for this design. >