[Show abstract][Hide abstract] ABSTRACT: The upgrade of the LHC collimation system includes
additional collimators in the LHC lattice. The longitudinal space
for the collimators can be obtained by replacing some LHC main
dipoles with shorter but stronger dipoles compatible with the LHC
lattice and the existing powering circuits, cryogenics, and beam
vacuum. A joint development programme aiming at building a
5.5 m long two-in-one aperture Nb3Sn dipole prototype suitable
for installation in the LHC is being conducted by FNAL and
CERN. As part of the first phase of the programme, 1 m and
2 m long single aperture models are being built and tested. Later
on, the collared coils from these models will be assembled and
tested in a two-in-one aperture configuration in both laboratories.
A 2 m long practice model made of a single coil wound with Nb3Sn
cable, MBHSM101, was developed and constructed at CERN. It
has been completed, and tested at both 4.3 K and 1.9 K. This
practice model features collared coils based on removable pole
concept, S2-glass cable insulation braided over a mica layer, and
coil end spacers made of sintered stainless steel with springy legs.
The paper describes the main features of this practice model, the
main manufacturing steps and the results of the cold tests.
[Show abstract][Hide abstract] ABSTRACT: The luminosity upgrade of the large hadron collider (HL-LHC) requires the development of new type of superconducting cables based on advanced Nb3Sn strands. In the framework of the FP7 European project EUCARD, the cables foreseen for the HL-LHC project have been tested recently in a simplified racetrack coil configuration, the so-called Short Model Coil (SMC). In 2013-2014, two SMCs wound with 40-strand (RRP 108/127) cables, with different heat treatment processes, reached during training at 1.9 K a current and peak magnetic field of 15.9 kA, 13.9 T, and 14.3 kA, 12.7 T, respectively. Using the measured signals from the voltage taps, the behavior of the quenches is analyzed in terms of transverse and longitudinal propagation velocity and hot-spot temperature. These measurements are compared with both analytical and numerical calculations from adiabatic models. The coherence of the results from the presented independent methods helps in estimating the relevance of the material properties and the adiabatic assumption for impregnated Nb3Sn conductor modeling.
[Show abstract][Hide abstract] ABSTRACT: The recently developed Coupling-Loss-Induced Quench (CLIQ) protection system is a new method for initiating a fast and voluminous transition to the normal state for protecting high energy density superconducting magnets. Its simple and robust electrical design, its lower failure rate, and its more efficient energy deposition mechanism make CLIQ often preferable to other conventional quench protection methods. The system is now implemented for the protection of a two meter long superconducting quadrupole model magnet and as such fully characterized in the CERN magnet test facility. Test results convincingly show that CLIQ allows for a more global quench initiation and thus a faster discharge of the magnet energy than conventional quench heaters. Nevertheless, the CLIQ performance is strongly affected by the length of the magnet to protect, hence an optimization is required for effective application to full size magnets. A series of measures for the optimization of a quench protection system for a quadrupole magnet based on CLIQ is outlined here. The impact of various key parameters on CLIQ’s performance, the most efficient CLIQ configuration, and the advantage of installing multiple CLIQ units are assessed.
[Show abstract][Hide abstract] ABSTRACT: The design and construction of a 120-mm wide-aperture, Nb-Ti superconducting quadrupole magnet for the Large Hadron Collider (LHC) insertion region is part of a study towards a luminosity upgrade of the LHC at CERN, envisaged for 2020-22. The main challenges for this accelerator quality magnet are to operate reliably with the high heat and radiation loads that are predicted in the insertion magnet regions. Calculations give approximately 500 Watts over the 30-m-long string of insertion magnets, while today LHC is operating for a nominal heat load of 12 Watts. To extract this heat, the model magnets incorporate new features: Open cable insulation, open ground insulation, open magnet structure, and a quench heater that has open channels to help extract the steady state heat load. This paper presents results from tests at room temperature and 1.8 K for the initial model magnet. We report magnet training, transfer function and field quality measurements, quench heater performance, and heat extraction studies using imbedded heaters to simulate the deposited beam heating profile.
[Show abstract][Hide abstract] ABSTRACT: The requirement at CERN for 1 kA range High Temperature Superconducting (HTS) cables optimized for long electrical transfer has led to the design and assembly of a novel type of cable that can be made from pre-reacted MgB2, Bi-2223 or YBCO tapes. The cable consists of an assembly of twisted pairs, each of which is made from three superconducting tapes with the required copper stabilizer. The twisted pair cable is designed to transfer a DC current of ± 600 A in helium gas environment. The paper reports on the results of the electrical tests performed on twisted-pair cables of identical structure and made from commercially available MgB2, Bi-2223 and YBCO tapes. The twist pitch of the cables is adapted to match the mechanical properties of the different superconductors. Critical current tests were performed at both liquid helium and liquid nitrogen temperature. The electrical performance of several cables made from different conductors is reported and compared.
[Show abstract][Hide abstract] ABSTRACT: The interconnections between Large Hadron Collider (LHC) main dipole and quadrupole magnets are made of soldered joints of two superconducting cables stabilized by a copper bus bar. The 2008 incident revealed the possible presence of defects in the interconnections of the 13 kA circuits that could lead to unprotected resistive transitions. Since then thorough experimental and numerical investigations were undertaken to determine the safe operating conditions for the LHC. This paper reports the analysis of experimental tests reproducing defective interconnections between main quadrupole magnets. A thermo-electromagnetic model was developed taking into account the complicated sample geometry. Close attention was paid to the physical description of the heat transfer towards helium, one of the main unknown parameters. The simulation results are reported in comparison with the measurements in case of static He I cooling bath. The outcome of this study constitutes a useful input to improve the stability assessment of the 13 kA bus bars interconnections.
[Show abstract][Hide abstract] ABSTRACT: The test of the first LARP (LHC Accelerator Research Program) Long Quadrupole is a significant milestone toward the development of Nb<sub>3</sub>Sn quadrupoles for LHC (Large Hadron Collider) Luminosity Upgrades. These 3.7-m long magnets, scaled from the 1-m long Technological Quadrupoles, are used to develop our capabilities to fabricate and assemble Nb<sub>3</sub>Sn coils and structures with lengths comparable to accelerator magnet dimensions. The long quadruples have a target gradient of 200 T/m in a 90-mm aperture. Pre-stress and support are provided by an Al-shell-based structure pre-loaded using bladders and keys. The coils were fabricated at BNL and FNAL, the shell-based structure was designed and assembled at LBNL, the test is performed at FNAL. In this paper we present the final steps of the development of the first model (LQS01), several upgrades to the test facility, the test results of witness cables, and the short sample limit.
[Show abstract][Hide abstract] ABSTRACT: Feasibility study of Cu stabilized Nb<sub>3</sub>Al strand and Rutherford cable for the application to high field accelerator magnets are being done at Fermilab in collaboration with NIMS. The Nb<sub>3</sub>Al strand, which was developed and manufactured at NIMS in Japan, has a non-copper Jc of about 844 A/mm<sup>2</sup> at 15 Tesla at 4.2 K, a copper content of 50%, and filament size of about 50 microns. Rutherford cables with 27 Nb<sub>3</sub>Al strands of 1.03 mm diameter were fabricated and tested. Quench tests on a short cable were done to study its stability with only its self field, utilizing a high current transformer. A pair of 2 meter long Nb<sub>3</sub>Al cables was tested extensively at CERN at 4.3 and 1.9 K up to 11 Tesla including its self field with a high transport current of 20.2 kA. In the low field test we observed instability near splices and in the central region. This is related to the flux-jump like behavior, because of excessive amount of Nb in the Nb<sub>3</sub>Al strand. There is possibility that the Nb in Nb<sub>3</sub>Al can cause instability below 2 Tesla field regions. We need further investigation on this problem. Above 8 Tesla, we observed quenches near the critical surface at fast ramp rate from 1000 to 3000 A/sec, with quench velocity over 100 m/sec. A small racetrack magnet was made using a 14 m of Rutherford cable and successfully tested up to 21.8 kA, corresponding to 8.7 T.