A first model dipole is being built for a 16 Tesla blockcoil dipole for future hadron colliders. The design uses stress management: a support matrix that intercepts Lorentz stress between successive sections of the coil and bypasses it to prevent strain degradation of the superconductors and insulation. The block-coil methodology has also been used to design dipoles for 12 Tesla and 15 Tesla, in which the amount of superconductor is minimized by cabling copper stabilizer strands with superconductor strands. The 12 Tesla block-coil dipole requires only one-fifth as much superconductor as does a 12 Tesla cos θ dipole that is being developed elsewhere. INTRODUCTIONThe technology of superconducting dipoles determines the cost and performance of future hadron colliders. The field strength determines the relation between energy and circumference; the field quality and provisions for beam stability and synchrotron radiation determine the luminosity and lifetime of the colliding beams. Over the past several years much work has been done to relate the several requirements of a high-luminosity collider to the parameters of its magnets. A first example is synchrotron radiation. It was once thought that field strength beyond ~10 Tesla would create a problem from the heat deposited by synchrotron radiation in the cryogenic magnet. it is now realized that synchrotron radiation damping at high field strength can damp beam size and improve luminosity, and schema have been conceived (one presented below) whereby the synchrotron radiation can be absorbed at a higher temperature within the dipoles so that its refrigeration impact is reduced. A second example is aperture. It was once thought that an aperture radius of at least 2.5 cm was necessary to have acceptable growth times for single-beam and mode coupling instabilities. Several schema have been developed recently whereby such instabilities can be damped within a single turn, so that apertures as small as 1 cm can support stable beams. With presently available superconductors, the coil for a high-field dipole is thick compared to its inner radius, so that reducing aperture has the potential to dramatically reduce magnet cost. A third example is the impact of various multipoles upon beam growth mechanisms in a high-luminosity collider.With NbTi superconductor, it was possible to make strands with extremely small filament diameter (few µm) so that multipoles produced by persistent currents at injection energy were suppressed. NbTi cannot support fields higher than ~9 Tesla, and the superconductors that are used at higher fields (today Nb 3 Sn, in the future Bi-2212) currently have very large filament diameter (>50 µm) if fabrication is optimized for high current density. BLOCK COIL DESIGN STRATEGYWe are developing a new approach to dipole design, in which the coils are configured in rectangular blocks instead of the cos θ geometry used in most superconducting dipoles to date. We are currently building a 16 Tesla dual dipole embodying this approach. We report here the re...

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 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.

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.

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