A drone for triggering naval mines, which drone includes a drive having an electric motor for locomotion in the water, wherein the electric motor can be used additionally to trigger the naval mines during operation of the drone, by an external magnetic field formed by the operation of the electric motor. The electric motor includes a stationary stator and a rotor, which is mounted for rotation relative to the stator. The stator includes at least one magnetic and/or electromagnetic element for forming an excitation field. The rotor includes at least one armature winding, which electromagnetically interacts with the excitation field during operation of the electric motor, whereby a superordinate magnetic field is formed. The external magnetic field formed outside of the electric motor during operation is in the form of a constant magnetic field.

A superconductor magnet system (2) includes a cryostat (4), a superconductor bulk magnet (5), and a cryogenic cooling system (12). The bulk magnet (5) has at least N axially stacked bulk sub-magnets (6a-6c), with N≥3. Between each two axially neighboring bulk sub-magnets, an intermediate body (7a-7b) is arranged. The intermediate bodies (7a-7b) are made from a non-metallic thermal insulator material. The cryogenic cooling system (12) is adapted for independently controlling the temperature of each bulk sub-magnet (6a-6c), and has, for each bulk sub-magnet, a temperature sensor (16a-16c) for sensing the temperature of the respective bulk sub-magnet and an adjustment unit (13a-13c) for adjusting a heating power and/or a cooling power at the respective bulk sub-magnet.

A superconducting coil of embodiments includes a substrate having a curved surface, a superconducting wire wound on the curved surface, the superconducting wire having a first region and a second region facing the first region, a first resin layer surrounding the superconducting wire and including a plurality of first particles and first resin surrounding the first particles, and a second resin layer positioned between the first region and the second region, the second resin layer covering the first resin layer and including a plurality of second particles and second resin surrounding the second particles and being made of material different from material of the first resin.

The present invention provides for polycrystalline superconducting permanent magnets which are synthesized of doped superconducting (AE) Fe.sub.2As.sub.2 compounds, where AE denotes an alkaline earth metal, such as Ba, Sr, Mg or Ca. The superconducting permanent magnets of the present invention can be magnetized in their superconducting state by induced currents, resulting in trapped magnetization that scales with the size of the bulk material. The magnitude of the trapped field has been demonstrated to be over 1 T and is predicted to be over 10 T if the technology is scaled, which is much higher than the capabilities of permanent magnets and other superconducting polycrystalline bulks currently known in the art.

The present invention provides for polycrystalline superconducting permanent magnets which are synthesized of doped superconducting (AE) Fe.sub.2As.sub.2 compounds, where AE denotes an alkaline earth metal, such as Ba, Sr, Mg or Ca. The superconducting permanent magnets of the present invention can be magnetized in their superconducting state by induced currents, resulting in trapped magnetization that scales with the size of the bulk material. The magnitude of the trapped field has been demonstrated to be over 1 T and is predicted to be over 10 T if the technology is scaled, which is much higher than the capabilities of permanent magnets and other superconducting polycrystalline bulks currently known in the art.

A charging and field supplement circuit for superconducting magnets based on a pulsed current includes a capacitor charging circuit, an energy-storage capacitor, a capacitor discharging circuit, a superconducting magnetic energy storage circuit, and a superconducting persistent-current switch. Two output ends of the capacitor charging circuit are respectively connected to two ends of the energy-storage capacitor. Two input ends of the capacitor discharging circuit are respectively connected to the two ends of the energy-storage capacitor. Two output ends of the capacitor discharging circuit are respectively connected to two input ends of the superconducting magnetic energy storage circuit. Two output ends of the superconducting magnetic energy storage circuit are respectively connected to two input ends of the superconducting persistent-current switch. Two output ends of the superconducting persistent-current switch are configured to charge and magnetize a target superconducting magnet.

A cold storage material particle of an embodiment includes at least one first element selected from the group consisting of a rare earth element, silver (Ag), and copper (Cu) and a second element that is different from the first element and forms a multivalent metal ion in an aqueous solution, in which an atomic concentration of the second element is 0.001 atomic % or more and 60 atomic % or less, and a maximum value of volume specific heat at a temperature of 20K or less is 0.3 J/cm.sup.3.Math.K or more.

A cold storage material particle of an embodiment includes at least one first element selected from the group consisting of a rare earth element, silver (Ag), and copper (Cu) and a second element that is different from the first element and forms a multivalent metal ion in an aqueous solution, in which an atomic concentration of the second element is 0.001 atomic % or more and 60 atomic % or less, and a maximum value of volume specific heat at a temperature of 20K or less is 0.3 J/cm.sup.3.Math.K or more.

A refrigerator is provided, including rare earth cold accumulating material particles filled in a cold accumulating vessel. The rare earth cold accumulating material particles are a rare earth oxide or a rare earth oxysulfide. The rare earth cold accumulating material particles define a sintered body. An average crystal grain size of the sintered body is 0.5 to 5 μm, a porosity of the sintered body is 10 to 50 vol. %, and an average pore size of the sintered body is 0.3 to 3 μm. In an arbitrary cross-section of the rare earth cold accumulating material particles, a number of pores per a unit area of 10 μm×10 μm is 20 to 70.

An active feedback controller for a power supply current of a no-insulation (NI) high-temperature superconductor (HTS) magnet to reduce or eliminate the charging delay of the NI HTS magnet and to linearize the magnet constant.