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.