G. Ganetis

High Field HTS R&D Solenoid for Muon Collider

This paper presents the goal and status of the high field High Temperature Superconductor (HTS) solenoid program funded through a series of SBIRs. The target of this R&D program is to build HTS coils that are capable of producing fields greater than 20 T when tested alone and approaching 40 T when tested in a background field magnet. The solenoid will be made with second generation (2G) high engineering current density HTS tape. To date, 17 HTS pancake coils have been built and tested in the temperature range from 20 K to 80 K. Quench protection, high stresses and minimization of degradation of conductor are some of the major challenges associated with this program.

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.

About the mechanics of SSC dipole magnet prototypes

During the last two years, nine 4‐cm aperture, 17‐m‐long dipole magnet prototypes were produced by Brookhaven National Laboratory (BNL) under contact with the Superconducting Super Collider (SSC) Laboratory. These prototypes are the last phase of a half‐decade‐long R&D program, carried out in collaboration with Fermi National Accelerator Laboratory and Lawrence Berkeley Laboratory, and aimed at demonstrating the feasibility of the SSC main‐ring dipole magnets. They also lay the groundwork for the 5‐cm‐aperture dipole magnet program now underway. After reviewing the design features of the BNL 4‐cm‐aperture, 17‐m‐long dipole magnets, we describe in detail the various steps of their fabrication. For each step, we discuss the paramaters that need to be mastered, and we compare the values that were achieved for the nine most recent prototypes. The data appear coherent and reproducible, demonstrating that the assembly process is under control. We then analyze the mechanical behavior of these magnets during cool...

Superconducting magnet system at the 50 GeV proton beam line for the J-PARC neutrino experiment

A neutrino oscillation experiment using the J-PARC 50 GeV 0.75 MW proton beam is planned as a successor to the K2K project currently being operated at KEK. A superconducting magnet system is required for the arc section of the primary proton beam line to be within the space available at the site. A system with 28 combined function magnets is proposed to simplify the system and optimize the cost. The required fields for the magnets are 2.6 T dipole and 19 T/m quadrupole. The magnets are also required to have a large aperture, 173.4 mm diameter, to accommodate the large beam emittance. The magnets will be protected by cold diodes and cooled by forced flow supercritical helium produced by a 4.5 K, 2/spl sim/2.5 kW refrigerator. This paper reports the system overview and the design status.

Tests of full scale SSC R&D dipole magnets

Four full-scale SSC (Superconducting Super Collider) research and development dipole magnets, incorporating successive mechanical design improvements, have been quench-tested. Three of the magnets are heavily instrumented with sensors to measure their mechanical behavior and verify the effectiveness of the mechanical improvements and with multiple voltage taps to locate the origin of quenches. The last two magnets of this series reach the SSC design operating field of 6.6 T in two or fewer quenches. Load cells and motion sensors show that in these two magnets the azimuthal clamping stress is higher at zero current and drops more slowly with excitation that in previous long magnets, and that the axial motion of the coil upon excitation has been greatly reduced. Quenches are found to originate preferentially in several locations, suggesting other design improvements. >

Initial test of a fast-ramped superconducting model dipole for GSI'S proposed SIS200 accelerator

Gesellschaft fur Schwerionenforschung (GSI) has proposed a large expansion of the existing facility in Darmstadt, Germany. The proposal includes an accelerator, SIS200, with rigidity of 200 T/spl middot/m that utilizes 4 T superconducting dipoles ramped at 1 T/s. An R&D program including both the superconductor and the magnet is directed at achieving the desired ramp rate with minimal energy loss. The RHIC arc dipoles, with 8 cm aperture, possess adequate aperture and field strength but are ramped at only 1/20 of the desired rate. However, for reasons of speed and economy, the RHIC dipole is being used as the basis for this work. The superconductor R&D has progressed far enough to permit the manufacture of an initial cable with satisfactory properties. This cable has been used in the construction of a 1 m model magnet, appropriately modified from the RHIC design. The magnet has been tested successfully at 2 T/s to 4.38 T.

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}

Full-length SSC R&D dipole magnets instrumented with four voltage taps on each turn of the inner quarter coils have been tested. These voltage taps enable (1) accurate location of the point at which the quenches start and (2) detailed studies of quench development in the coil. Attention here is focused on localizing the quench source. After recalling the basic mechanism of a quench (why it occurs and how it propagates), the method of quench origin analysis is described: the quench propagation velocity on the turn where the quench occurs is calculated, and the quench location is then verified by reiterating the analysis on the adjacent turns. Last, the velocity value, which appears to be higher than previously measured, is discussed.

Racetrack Coils Supported by Full-Length and Segmented Shell Structures

The new heavy ion synchrotron proposed by GSI will comprise two superconducting magnet rings in the same tunnel, having rigidities of 200 T.m and 100 T.m. Fast ramp times are needed, which can cause significant problems for the magnets, particularly in the areas of ac loss and field distortion. This paper discusses the 200 T.m ring, which will use Cos /spl theta/ magnets based on the RHIC dipole design. We describe options for the low loss Rutherford cable that will be used, together with a novel insulation scheme designed to promote efficient cooling. Measurements of contact resistance in the cable are presented and the results of these measurements are used to predict the ac losses, temperature rise and field distortion in the magnets during fast ramp operation.

Quench Start Localization in Full-Length SSC R&D Dipoles

The new heavy ion synchrotron facility proposed by GSI will have two superconducting magnet rings in the same tunnel, with rigidities of 300 T /spl middot/ m and 100 T /spl middot/ m. Fast ramp times are needed. These can cause problems of ac loss and field distortion in the magnets. For the high-energy ring, a 1-m model dipole magnet has been built, based on the RHIC dipole design. This magnet was tested under boiling liquid helium in a vertical dewar. The quench current showed very little dependence on ramp rate. The ac losses, measured by an electrical method, were fitted to straight-line plots of loss/cycle versus ramp rate, thereby separating the eddy current and hysteresis components. These results were compared with calculated values, using parameters which had previously been measured on short samples of cable. Reasonably good agreement between theory and experiment was found, although the measured hysteresis loss is higher than expected in ramps to the highest field levels.