The Cryogenic Performance of NbTi Superconductor Wire Linear Actuators

Abstract

We describe the results of superconductor wire linear actuator (“voice coil”) experiments at temperatures as low as 4 K for two superconductor coils. Both coils are wound with multifilamentary NbTi superconductor wire. The superconductor filaments of the first actuator are embedded in a copper-nickel alloy matrix; the filaments of the second actuator are embedded in a high-purity copper matrix. The electromagnetic force interaction is provided by the ~0.5 T field of a permanent magnet assembly fabricated from 28 MGOe energy product samarium cobalt and nickel steel. We extend our NbTi/Cu matrix investigation by describing the temperature dependence (4 to 11 K) of the ac power dissipation, natural frequency, and damping parameters. Data is presented for a range of temperatures both slightly above and slightly below the coil’s critical temperature. Our study indicates that due to loss mechanisms other than the resistive losses which dominate at room temperature, careful consideration must be given to the design and material choice of cryogenic linear actuators. Coil resistivity minimization does not necessarily correspond to minimal total power dissipation at cryogenic temperatures.