I. Introduction
The new generation of superconductor synchronous motors are provided with high temperature superconductor (HTS), high current density field windings that request special cooling technologies: the rotor is designed as a compact structure with cryogenically cooled HTS coils. These machines have substantial advantages when compared to their classical counterparts: they are (20–30%) lighter for the same rated power, much smaller sizes, greater power density (the HTS wires conduct more than 140 times the current of conventional copper wires with the same dimensions while delivering two to three times more power per unit weight), higher durability / longer life, and significant higher efficiency [1]–[5].