A hybrid-coil NbJSn/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 NbJSn 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 colliderquality field over a 2O:l 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.

Abstract-A family of high-field dipoles is being developed at Texas A&M University, as part of the program to improve the cost-effectiveness of superconducting magnet technology for future hadron colliders. The TAMU technology employs stress management, flux-plate control of persistent-current multipoles, conductor optimization using mixed-strand cable, and metalfilled bladders to provide pre-load and surface compliance. Construction details and status of the latest model dipole will be presented.

The NbTi model dipole TAMU1 was successfully tested at Lawrence Berkeley Lab. The dipole reached 88% of short-sample current on the first quench, and trained rapidly to 98%. The incorporated quench heaters were capable of inducing a plateau quench in <10 msec. The splice resistance was measured to be 0.28 nΩ in the multi-kA range, indicating an excellent contact. AC loss properties were studied during ramp studies. Ramps to 1,000 A/s (0.9 T/s) operated at greater than 60% plateau current. The dipole is a success. It is significant that this high-field NbTi dipole operated successfully at shortsample current with minimal training, even though the coil was vacuum-impregnated with epoxy. We attribute this performance in part to the stress management that is integrated into the block-coil geometry.

The second phase of development of a new high-field dipole technology has been completed. A model dipole employing wind/react Nb 3 Sn 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.

A direct-braid fiberglass cloth insulation has been developed and evaluated for use on Nb 3 Sn 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.