Al McInturff

Development and Coil Fabrication for the LARP 3.7-m Long Nb3Sn Quadrupole

The U.S. LHC Accelerator Research Program (LARP) has started the fabrication of 3.7-m long Nb3Sn quadrupole models. The Long Quadrupoles (LQ) are ldquoProof-of-Principlerdquo magnets which are to demonstrate that Nb3Sn technology is mature for use in high energy particle accelerators. Their design is based on the LARP Technological Quadrupole (TQ) models, developed at FNAL and LBNL, which have design gradients higher than 200 T/m and an aperture of 90 mm. The plans for the LQ R&D and a design update are presented and discussed in this paper. The challenges of fabricating long accelerator-quality Nb3Sn coils are presented together with the solutions adopted for the LQ coils (based on the TQ experience). During the fabrication and inspection of practice coils some problems were found and corrected. The fabrication at BNL and FNAL of the set of coils for the first Long Quadrupole is in progress.

Test Results of LARP 3.6 m

As part of the LHC Accelerator Research Program (LARP) to build a high performance quadrupole magnet with Nb3Sn conductor, a pair of 3.6 m-long Nb3Sn racetrack coils has been made at Brookhaven National Laboratory (BNL) and installed in two shell-type support structures built by Lawrence Berkeley National Laboratory (LBL). These magnet assemblies have been tested at 4.5 K at BNL to gauge the effect of extended length and prestress on the mechanical performance of the long structure compared to earlier short models. This paper presents the results of quench testing and compares the overall performance of the two versions of the support structure. We also summarize the shell strain measurements and discuss the variation of quench current with ramp rate.

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

The US LHC Accelerator Research Program (LARP) is developing Nb3Sn prototype quadrupoles for the LHC interaction region upgrades. Several magnets have been tested within this program and understanding of their behavior and performance is a primary goal. The instrumentation is consequently a key consideration, as is protection of the magnet during quenches. In all LARP magnets, the flexible circuits traces combine the instrumentation and the protection heaters. Their fabrication relies on printed circuit technology based on a laminate made of a 45-micron thick kapton sheet and a 25-micron thick foil of stainless steel. This paper reviews the protection heaters designs used in the TQ (Technology Quadrupole) and LR (Long Racetrack) series as well as the one used in LBNL HD2a high field dipole and presents the design of the traces for the Long Quadrupole (LQ), addressing challenges associated with the stored energy and the length of the magnet.

Racetrack Coils Supported by Full-Length and Segmented Shell Structures

The US LHC Accelerator Research Program (LARP) is developing Nb3Sn prototype quadrupoles for the LHC interaction region upgrades. Several magnets have been tested within this program and understanding of their behavior and performance is a primary goal. The instrumentation is consequently a key consideration, as is protection of the magnet during quenches. In all LARP magnets, the flexible circuits traces combine the instrumentation and the protection heaters. Their fabrication relies on printed circuit technology based on a laminate made of a 45-micron thick kapton sheet and a 25-micron thick foil of stainless steel. This paper reviews the protection heaters designs used in the TQ (Technology Quadrupole) and LR (Long Racetrack) series as well as the one used in LBNL HD2a high field dipole and presents the design of the traces for the Long Quadrupole (LQ), addressing challenges associated with the stored energy and the length of the magnet.

Instrumentation and Quench Protection for LARP Magnets

A structured cable has been developed and tested for use in insert windings for high-field solenoids. The cable utilizes a design developed earlier, in which six strands of multi-filament Bi-2212/Ag round wire are cabled around a thin-wall spring tube and jacketed in a high-strength Inconel sheath. The cable provides stress management within each winding so that coil stress cannot degrade the fragile superconducting filaments. The cable-based coil accommodates inward pre-load, giving the potential for twice the achievable field increment per shell. Prototype lengths of cable have been prepared and a heat treatment schedule has been optimized. Test results are presented for the performance of small test windings.

Instrumentation and Quench Protection for LARP

A technology for accelerator-driven subcritical fission in a molten salt core (ADSMS) is being developed as a basis for the destruction of the transuranics in used nuclear fuel. The molten salt fuel is a eutectic mixture of NaCl and the chlorides of the transuranics and fission products. The core is driven by proton beams from a strong-focusing cyclotron stack. This approach uniquely provides an intrinsically safe means to drive a core fueled only with transuranics, thereby eliminating competing breeding terms.

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

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.

Magnets

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

Bi-2212 Structured Cable for High-Field Solenoid Inserts

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.

Accelerator-driven subcritical fission in molten salt core: Closing the nuclear fuel cycle for green nuclear energy

The Alpha Magnetic Spectrometer (AMS) is a particle detector designed to search for anti-matter, dark matter and the origin of cosmic rays in space. A superconducting magnet has been developed to generate 0.78 T field at the center. The magnet system consists of a pair of large “dipole” coils together with two series of six racetrack coils, arranged circumferentially in order to minimize the stray field. The coils, series connected, are wound with an aluminum-stabilized mono-strand NbTi conductor and are cooled by a superfluid helium circuit. The superconducting magnet was successfully tested up to the operating current of 410 A, however the decision was taken to equip the spectrometer with a NdFeB permanent magnet in order to maximize the experiment life. The paper describes the results of the superconducting magnet tests and in particular analyses an anomalous increasing of the coil temperature during magnet charging.