Andrew Jaisle

Stress management in high-field dipoles

The management of Lorentz stress and preload forces is the biggest single challenge in the effort to develop collider dipoles with ever greater field strength. Were the Lorentz forces permitted to accumulate through a coil, they would exceed the limit for strain degradation for the A15 and high-temperature superconductors which are capable of sustaining such field strength. A strategy has been devised for intercepting Lorentz stress within the coil to overcome this problem in high-field block-coil dipoles. The coil is fabricated in multiple independent shells, in which a high-strength structure and a soft-modulus spring are used to bypass stress between succeeding layers. Finite-element analysis and experimental studies have demonstrated that this strategy can limit the maximum stress anywhere in a coil so that it nowhere exceeds strain degradation limits for fields at least to 20 Tesla.

16 tesla Nb/sub 3/Sn dipole development at Texas A&M University

A 16 Tesla Nb/sub 3/Sn block-coil dual dipole is being developed to extend the available field strength for future hadron colliders. The design incorporates several novel features. Current programming of 3 independent coil elements is used to control all multipoles over a 20:1 dynamic range of dipole field. Stress management, comprising a lattice of ribs and plates integrated into the coil structure, is used to distribute preload and Lorentz forces so that the stress in the coil never exceeds 100 MPa. Distributed cooling, utilizing spring elements in each coil block, intercepts heat generated by synchrotron radiation and beam losses. Rectangular pancake coil geometry accommodates simple fabrication and direct preload in the direction of Lorentz forces. The bore diameter can be optimized for collider requirements (2.5 cm for 50 TeV/beam vs, 5 cm for 8 TeV/beam), so that a 16 Tesla block-coil dipole for 50 TeV/beam requires the same amount of superconductor/TeV as the 8.5 Tesla LHC dipole for 8 TeV/beam. A first model of the dipole is currently being built.

Block-coil dipole for future hadron colliders

A first model dipole is being built for a block-coil dipole for future hadron colliders. The design incorporates stress management, in which Lorentz stress is intercepted between successive sections of the coil and bypassed through a support matrix. By controlling stress, the dipole should make it possible to utilize Nb/sub 3/Sn and BSCCO superconductors without strain degradation at high field. The first model dipole is being built using NbTi cable in order to evaluate fabrication techniques and stress management performance.

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

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.

Block-Coil Dipole

High-field (12-18 Tesla) superconducting magnets are required to enable an increase in the energy of future colliders. Such field strength requires the use of Nb3Sn superconductor, which has limited tolerance for compressive and shear strain. A strategy for stress management has been developed at Texas A&M University and is being implemented in TAMU3, a short-model 14 Tesla stress-managed Nb3Sn block dipole. The strategy includes the use of laminar capacitive stress transducers to monitor the stresses within the coil package. We have developed fabrication techniques and fixtures, which improve the reproducibility of the transducer response both at room temperature and during cryogenic operation. This is a report of the status of transducer development.