Development of persistent current switch for high temperature superconducting coils (2000-2003)

PCS based on YBCO film (THEVA  http://www.theva.com/)

This PCS consists of sapphire disk #100mm dia with patterned YBCO layer on one side.  Nichrome (ρ=1.1 × 10-6 Ωm) heater with resistance of 120Ω was sputtered on other side of the disk. The contacts areas on both sides were covered with a gold layer to allow soldering of the current leads.

PCS based on BSCCO non-inductive coil. The resistance of PCS coil in the normal state is 2.1-2.8 Ohm for temperatures 108K (SC transition) to 300 K respectively.

Multilayer coil consists of alternate layers of the superconducting tape, heater SS tape and copper tape. Such design have to ensure fast heating and cooling of the superconductor and thus its fast transition to normal state and fast return to superconducting state. The transition time from the SC state to the normal state and vice versa was about 10 s.

Low resistance electrical contacts are necessary for PCS

We have made an impressive progress in the development of low resistance electrical contacts, in the level of 10^-8Ω. 

We concluded that superconducting PCS is not suitable for power applications (SMES) mostly because of long operation time and low resistance in closed state.

Results of this research can be used in development the resistive Fault Current Limiter (FCL) that has many common features with PCS.