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 cooldown and excitation, and we attempt to relate this behavior to the magnet features The data reveal that the mechanical behavior is sensitive to the collar‐yoke interference and that the magnets exhibit somewhat erratic changes in coil end‐loading during cooldown

About the mechanics of SSC dipole magnet prototypes

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. >

Tests of full scale SSC R&D dipole magnets

New requirements for thermal insulation include robust Multilayer insulation (MU) systems that work for a range of environments from high vacuum to no vacuum. Improved MLI systems must be simple to install and maintain while meeting the life-cycle cost and thermal performance objectives. Performance of actual MLI systems has been previously shown to be much worse than ideal MLI. Spacecraft that must contain cryogens for both lunar service (high vacuum) and ground launch operations (no vacuum) are planned. Future cryogenic spacecraft for the soft vacuum environment of Mars are also envisioned. Industry products using robust MLI can benefit from improved cost-efficiency and system safety. Novel materials have been developed to operate as excellent thermal insulators at vacuum levels that are much less stringent than the absolute high vacuum requirement of current MLI systems. One such robust system, Layered Composite Insulation (LCI), has been developed by the Cryogenics Test Laboratory at NASA Kennedy Space Center. The experimental testing and development of LCI is the focus of this paper. LCI thermal performance under cryogenic conditions is shown to be six times better than MLI at soft vacuum and similar to MLI at high vacuum. The experimental apparent thermal conductivity (k-value) and heat flux data for LCI systems are compared with other MLI systems.

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Robust multilayer insulation for cryogenic systems

The test facility used for R&D testing of full scale development dipole magnets for the SSC is described. The Fermilab Magnet Test Facility, originally built for production testing of Tevatron magnets, has been substantially modified to allow testing also of SSC magnets. Two of the original six test stands have been rebuilt to accommodate testing of SSC magnets at pressures between 1.3 Atm and 4 Atm and at temperatures between 1.8 K and 4.8 K and the power system has been modified to allow operation to at least 8 kA. Recent magnets have been heavily instrumented with voltage taps to allow detailed study of quench location and propagation and with strain gage based stress, force and motion transducers. A data acquisition system has been built with a capacity to read from each SSC test stand up to 220 electrical quench signals, 32 dynamic pressure, temperature and mechanical transducer signals during quench and up to 200 high precision, low time resolution, pressure, temperature and mechanical transducer signals. The quench detection and protection systems is also described.

Fermilab r&d test facility for ssc magnets

Test results for a high quality industrial superinsulation

The thermal performance of three candidate thermal insulation systems for the SSC magnet cryostat has been evaluated experimentally in a heat leak test facility. The systems evaluated were multilayer insulation (MLI) blankets consisting of aluminized polyester film with fiberglass mat spacer, aluminized polyester film with spunbonded nylon spacer and aluminized dimpled perforated polyester film without spacer. Performance between 300 and 80 K with good and degraded insulating vacuum was studied. The inter-layer heat transfer coefficient hitl and the effective thermal conductivity Keff of MLI blanket were used to compare the different insulation systems and to predict the performance of the SSC magnet insulation.

Thermal Performance of Candidate SSC Magnet Thermal Insulation Systems

The second-generation cryostat design for the Superconducting Super Collider has been developed utilizing the experiences gained during the construction, installation and operation of several full-length first-generation dipole magnet models. The nature of the cryostat improvements is described. Considered are the connections between the magnet cold mass and its supports, cryogenic supports, cold mass axial anchor, thermal shields, insulation, vacuum vessel, and interconnections. The details of the improvements are enumerated and the results of available component and system evaluations are presented. >

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Superconducting Super Collider second generation dipole magnet cryostat design

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.

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Full length prototype SSC dipole test results

The SSC Magnet Development Program is developing accelerator dipole magnets in successive iterations. The initial iteration is complete with six full length model magnets and a thermal model having been built and tested. This initial experience along with the evolving SSC Magnet System Requirements have resulted in the second generation magnet cryostat design. It is this configuration that will be employed for the near term ongoing magnetic, thermal, string and accelerated life testing and will be the design considered for Phase I; i.e., Technology Orientation, of the SSC Magnet Industrialization Program. 5 refs., 7 figs., 1 tab.

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T. Ohmori

Papers

Thermal Performance of Candidate SSC Magnet Thermal Insulation Systems

Superconducting Super Collider second generation dipole magnet cryostat design

Full length prototype SSC dipole test results

Second generation superconducting super collider dipole magnet cryostat design