Trial production and experiments of linear actuator with HTS bulk secondary

To investigate characteristics of a linear actuator with high-temperature superconducting (HTS) bulk secondary, a short secondary type linear actuator has been designed and constructed. The actuator is comprised of an YBCO bulk secondary (mover) and copper windings with iron core (primary). A zero-field-cooled bulk located at the center of the actuator plays a role of generating thrust, while four field-cooled (trapped field) bulks are used for levitation and guidance of the secondary. We measured the starting thrust force and magnetic field distribution in the air gap. We developed a simulation program based on the finite element method (FEM) taking the voltage-current (E-J) characteristics of the bulk into consideration to investigate electromagnetic behaviors within the bulk exposed to a time-varying magnetic field. Agreement between experiment and simulation is good, and it validates the simulation program and the presented assumptions in the numerical approach. Using the simulation program, we investigated the dependency of n-value and critical current density of the bulk material on the magnetic flux density in the air gap and the starting thrust force. Supercurrent density within the bulk is a key factor for the magnetic flux density and the thrust force.