10 kA joints for HTS roebel cables

Future high temperature superconductor (HTS) high field magnets using multitape HTS cables need 10-kA low-resistance connections. The connections are needed between the poles of the magnets and at the terminals in a wide-operating temperature range, from 1.9-85 K. The EuCARD-WP10 Future Magnets collaboration aims at testing HTS-based Roebel cables in an accelerator magnet. Usually, low temperature superconductor (LTS) cables are jointed inside a relatively short soldered block. Powering tests at CERN have highlighted excess heating of a joint following classical LTS joint design. The HTS Roebel cables are assembled from REBCO-coated conductor tapes in a transposed configuration. Due to this, the tapes surface the cable at an angle with the cable axis. A low-resistance joint requires a sufficiently large interface area for each tape. Within one twist pitch length, each tape is located at the surface of the cable over a relatively small non-constant area. This geometry prevents making a well-controlled joint in a compact length along the cable. This paper presents a compact joint configuration for the Roebel cable overcoming these practical challenges. A new joint called fin-block is designed. The joint resistance is estimated computationally. Finally, the test results as a function of current and temperature are presented

Effective Time Constants at 4.2 to 70 K in ReBCO Pancake Coils with Different Inter-Turn Resistances

For future ReBCO tape based accelerator magnets it is proposed to use no- or partial inter-turn insulation to deal with quench detection and protection. In a non-insulated coil the turns are separated by a finite electrical resistance, providing a bypass for the current at hot-spots, improving thermal stability and quench detection time. However, such coils show different dynamic electromagnetic behavior compared to insulated coils under normal charging and transient quench conditions. To study such coils in detail two pancake coils, one dry-wound and one with solder in between turns, are prepared and tested in a variable temperature cryostat between 4.2 and 70 K. Properties of the coils that are studied are charge and discharge time behavior, turn-to-turn resistance, response to current stepping, and operational stability. In this paper, the first results are presented and compared to a simplified network model in order to gain further understanding into the underlying physics

Assembly and Test of the HL-LHC Twin Aperture Orbit Corrector Based on Canted Cos-Theta Design

In the frame of the high-luminosity upgrade project (HL-LHC) at CERN, a double aperture, independently powered, family of beam orbit corrector magnets will be installed close to the two main LHC experiments Atlas and CMS. These 2.6 T magnets, built using a canted cos-theta design. This paper describes the development of the prototype, full size 2-m-long magnets. We first focus on design and assembly techniques: from coil winding using a CNC machined aluminium former to impregnation, layer-jump, quench protection, and yoke assembly. We then present the power test results at 1.9 K: training, field quality and protection

Design, Assembly, and Test of the CERN 2-m Long 11 T Dipole in Single Coil Configuration

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 Nb_3Sn 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 Nb_3Sn 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