For future 20+ T accelerator type magnets, ReBCO superconductors are ideal for their high current density in high magnetic field. At CERN, demonstrator dipole magnets using ReBCO conductor are being developed in order to study their feasibility. In this work, a design of a cloverleaf-racetrack magnet is presented, which consist of two poles. A key problem in such magnets is how to realize the coil-ends without causing degradation due to coil winding, cool down and operation. The cloverleaf geometry accommodates the particle beam pipe without any hard-way ReBCO tape bending. To design such geometry of the coil-end, a new method using Bézier splines is presented. The ReBCO coils are wound with dual tape conductor where the ReBCO layers are facing each other. For quench protection, the coils are non-insulated, allowing the coil current at quench to redistribute transversally through the winding pack. A comparison between dry-wound and soldered non-insulated coils is made. Progress on the electromagnetic and mechanical design of the cloverleaf magnet is reported in this paper.
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.
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