J. Cozzolino

Second Generation HTS Quadrupole for FRIB

Quadrupoles in the fragment separator region of the Facility for Rare Isotope Beams (FRIB) will be subjected to very large heat loads (over 200 Watts) and an intense level of radiation (~10 MGy per year) into the coils of just the first magnet. Magnets made with High Temperature Superconductors (HTS) are advantageous over conventional superconducting magnets since they can remove these heat loads more efficiently at higher temperatures. The proposed design is based on second generation (2G) HTS which allows operation at ~50 K. 2G has been found to be highly radiation tolerant. The latest test results are summarized. The goal of this R&D program is to evaluate the viability of HTS in a real machine with magnets in a challenging environment where HTS offers a unique solution.

Tuning shims for high field quality in superconducting magnets

A high field quality in quadrupoles for the interaction region is crucial to the luminosity performance of high energy colliders such as the Relativistic Heavy Ion Collider (RHIC). The field quality in magnets is limited in part by manufacturing tolerances in the parts and assembly. A tuning shim method has been developed to reduce the relative field errors (/spl Delta/B/B) from /spl sim/10/sup -4/ to /spl sim/10/sup -5/ at 2/3 of the coil radius. Eight tuning shims having a variable thickness of iron are inserted after the construction and measurement of field harmonics in the magnet. In this paper the tuning shim technique is described for RHIC interaction region quadrupoles. The results of calculations and measurement are also presented.

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}

This paper presents a summary of the design, construction and test results of a common coil dipole DCC017 made using ldquoreact & windrdquo Nb3Sn technology. It reached the computed short sample field of 10.2 T at 10.8 kA after a number of quenches. In order to build high field magnets with brittle pre-reacted superconductors one must develop magnet designs, tooling and construction techniques that keep conductor degradation due to bending and handling to a tolerable level. The successful construction and test of this magnet demonstrates that it is possible to design and build magnets in the 10 (plus) T range using ldquoreact & windrdquo technology. The magnet is based on a 2-layer common coil design with a clear horizontal space of 31 mm. A unique feature of the design is a tall 338 mm clear vertical open space that can facilitate possible flat racetrack coil testing in a high background field without dis-assembling the magnet.

Racetrack Coils Supported by Full-Length and Segmented Shell Structures

This paper presents the outcome of significant magnet R&D that was started over a decade ago towards solving one of the most critical issues in the design of the Facility for Rare Isotope Beams (FRIB) and resulted in the successful demonstration of a full size prototype HTS quadrupole for the fragment separator region. This magnet will be subjected to unprecedented radiation and heat loads. An HTS quadrupole, with more than a 12 K margin over the nominal 38 K operating temperature, provides a unique solution. After briefly presenting the design and construction, the test results will be discussed in more detail. An advanced quench protection system was able to protect the magnet against an accident which caused thermal run away (or quench) is also discussed. The magnet uses a significant amount of HTS from two leading manufacturers. The successful demonstration should encourage the use of HTS magnets where one must deal with a large amount of radiation and/or energy deposition.

React and Wind

An alternative structure for the 120 mm Nb3Sn quadrupole magnet presently under development for use in the upgrade for LHC at CERN is presented. The goals of this structure are to build on the existing technology developed in LARP with the LQ and HQ series magnets and to further optimize the features required for operation in the accelerator. These features include mechanical alignment needed for field quality and provisions for cold mass cooling with 1.9 K helium in a helium pressure vessel. The structure will also optimize coil azimuthal and axial pre-load for high gradient operation, and will incorporate features intended to improve manufacturability, thereby improving reliability and reducing cost.

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

This paper presents several magnetic designs for a 16-T 50-mm aperture Nb3Sn dipole based on the common coil design for a future circular collider. It has an aperture-to-aperture spacing of 250 mm, a yoke outer diameter of 700 mm, and uses a similar or less conductor amounts than cosine theta or block designs. All field harmonics are about an order of magnitude better than specified at the design field and well below the specification in the entire range of operation. Initial results of mechanical design and analysis are also encouraging. They indicate that the proposed structure is able to support the pole coil blocks against the vertical Lorentz forces and that the maximum stresses in all coils remain generally below 150 MPa. Given several inherent advantages of the common coil design, the development presented here should make this approach a leading candidate for very high field magnets in future colliders.

Common Coil Dipole

A support structure for the 120 mm Nb3Sn quadrupole magnet is presently under development for use in the upgrade for LHC at CERN. The design aims to build on existing technology developed in LARP with the LQ and HQ mag- nets and to further optimize the features required for operation in the accelerator. The structure and the proposed assembly methods include features for maintaining mechanical alignment of the coils to achieve the required field quality. It also includes a helium containment vessel and provisions for cooling with 1.9 K helium. The development effort includes the assembly of a 15 cm model to verify required coil load is achieved. Status of the R&D effort and an update on the magnet design, including its incorporation into the design of a complete one meter long cold mass is presented.

HTS Quadrupole for FRIB—Design, Construction and Test Results

The Superconducting Magnet Division at Brookhaven National Laboratory (BNL) has made 20 insertion region dipoles for the Large Hadron Collider (LHC) at CERN. These 9.45 m-long, 8 cm aperture magnets have the same coil design as the arc dipoles now operating in the Relativistic Heavy Ion Collider (RHIC) at BNL and are of single aperture, twin aperture, and double cold mass configurations. They are required to produce fields up to 4.14 T for operation at 7.56 TeV. Eighteen of these magnets have been tested at 4.5 K using either forced flow supercritical helium or liquid helium. The testing was especially important for the twin aperture models, whose construction was very different from the RHIC dipoles, except for the coil design. This paper reports on the results of these tests, including spontaneous quench performance, verification of quench protection heater operation, and magnetic field quality.

Alternative Mechanical Structure for LARP Nb

The Superconducting Magnet Division at Brookhaven National Laboratory (BNL) is building 20 insertion region dipoles of various types for the Large Hadron Collider (LHC) at CERN. These 9.45 m-long, 8 cm aperture magnets use the same coil design as the arc dipoles for the Relativistic Heavy Ion Collider (RHIC) at BNL. The most challenging of these dipoles are the twin aperture magnets. The two apertures are separated by 188 to 234 mm, and the dipole fields in both the apertures point in the same direction. In order to test the design and determine various operating parameters of these magnets, two three m-long prototypes were built and tested at BNL. Tests were done to measure spontaneous quench performance, conductor temperature at quench, coil stress behavior during cool-downs, warm-ups and excitation ramps, and quench protection heater performance. Extensive magnetic field measurements were done with a 3.58-meter long integral coil, as well as a one-meter long coil at the axial center of the magnet. Dynamic effects, such as time decay and snapback at injection, and harmonics due to cable magnetization and eddy currents were studied with a time resolution of 2 s.