Raymond Blackburn

12 Tesla hybrid block-coil dipole for future hadron colliders

A hybrid-coil Nb/sub 3/Sn/Cu dipole is being developed for use in future hadron colliders. It features stress management within the coil, and the use of pure Cu strands within the coil to minimize the quantity of superconductor while providing quench protection. A first 7 Tesla NbTi model of the design has been built and will soon be tested. Two designs for the first Nb/sub 3/Sn model have been prepared. In one version, the placement of coil blocks and the inside contour of the steel flux return are shaped to achieve collider-quality field over a 20:1 dynamic range of operating field. In the other version, the flux return provides a close-coupled planar boundary that suppresses persistent-current multipoles by a factor 20, and the same dynamic range is achieved using current programming of the inner and outer coil elements. Both versions use the least superconductor of any high-field collider dipole design.

Test Results of a

A second phase of a high field dipole technology development has been tested. A Nb3Sn block-coil model dipole was fabricated, using magnetic mirror geometry and wind/react coil technology. The primary objective of this phase was to make a first experimental test of the stress-management strategy pioneered at Texas A&M. In this strategy a high-strength support matrix is integrated with the windings to intercept Lorentz stress from the inner winding so that it does not accumulate in the outer winding. The magnet attained a field that was consistent with short sample limit on the first quench; there was no training. The decoupling of Lorentz stress between inner and outer windings was validated. In ramp rate studies the magnet exhibited a remarkable robustness in rapid ramping operation. It reached 85% of short sample(ss) current even while ramping 2-3 T/s. This robustness is attributed to the orientation of the Rutherford cables parallel to the field in the windings, instead of the transverse orientation that characterizes common dipole designs. Test results are presented and the next development phase plans are discussed.

{\rm Nb}_{3}{\rm Sn}

The second phase of development of a new high-field dipole technology has been completed. A model dipole employing wind/react Nb 3Sn cable and stress-managed block coil geometry was fabricated and will soon be tested at LBNL. The dipole features stress-strain management in its internal windings and metal-filled bladder preload. Pending validation of performance of these new features, the new technology should result in improved cost-effective fabrication of dipoles for 16 T and beyond. Construction experience and plans for the next phase of development are presented

Wind/React “Stress-Managed” Block Dipole

The current status of the Texas A&M superconducting magnet R&D program is reported. The program is implementing a design philosophy in which Lorentz stress is managed within the coils of a block-coil geometry, isostatic preload is delivered using an arrangement of pressurized Woods metal filled bladders, insulation utilizes fine-filament Silane-sized S-glass, and low-field multipoles are constrained by a flux plate integrated with the coil package. Construction progress on TAMU3 is reported and plans for a full-aperture dipole TAMU5 are discussed.

Construction of a Mirror-Configuration Stress-Managed

A direct-braid fiberglass cloth insulation has been developed and evaluated for use on Rutherford cable. The fabric is directly woven onto the cable, using fine-filament yarn sized with a silane mixture. The total thickness of the cloth on each face of the cable is ~55 microns. The sizing is compatible with subsequent reaction heat treat without decomposition, and provides improved wetting and adhesion in the final epoxy impregnation. Ten-stack assemblies of cable segments have been processed through typical coil heat treatment and impregnation and tested for high-voltage insulation and yield strength under mechanical shear.

rm Nb_3rm Sn

A superconducting test cavity and cryostat are being developed to support the testing of round wafer samples of new superconducting materials. The cavity is designed to test these samples in surface fields up to and beyond the BCS limit of Nb. The design is optimized to produce maximum surface field on the sample compared with that elsewhere in the cavity. It operates in the TE011 mode. A dielectric hemisphere of low-loss sapphire is located just above the wafer surface and serves to concentrate the surface field. The sapphire is cooled by a column of superfluid He, with sufficient heat transport to maintain high Q throughout the rf pulse. It should be possible to test a sample to twice the BCS limit of Nb while measuring the rf surface resistance of the sample.

Block-Coil Dipole

We report the construction and testing of components of TAMU3, a 14 Tesla Nb3Sn block-coil dipole. A primary goal in developing this model dipole is to test a method of stress management in which Lorentz stress is intercepted within the coil assembly and bypassed so that it cannot accumulate to a level that would cause strain degradation in the superconducting windings. Details of the fabrication, tooling, and results of construction and magnet component testing will be presented.

Current Status of the Texas A&M Magnet R&D Program

A 1.3 GHz test cavity has been designed to test wafer samples of superconducting materials. The surface magnetic field on the sample wafer is 3.75 times greater than anywhere else on the cavity surface. The cavity also facilitates measurement of the rf surface resistance corresponding to a Q of 1010. The cavity is operated in a TE01 mode. A high purity sapphire hemisphere is used to enhance the circulating field on the sample and suppress the fields on the remainder of the cavity surface. The sapphire purity must be tested for its loss tangent and dielectric constant. To test these properties a smaller sapphire rod of the same quality will be inserted into a CEBAF cavity operating in a TE01 mode. This will allow us to measure the temperature of the sapphire as a function of input energy and time, and the dielectric constant through its effect on the resonant frequency.