Lorentz force velocimetry using a bulk HTS magnet system: proof-of-concept
This paper presents a proof-of-concept of the idea of using bulk high-temperature superconducting (HTS) materials as quasi-permanent magnets that would form, in the future, an integral part of an advanced Lorentz force velocimetry (LFV) system. The experiments, calculations and numerical simulations are performed in accordance with the fundamental theory of LFV, whereby a moving metal rod passes through a static magnetic field, in our case generated by the bulk HTSs. The bulk HTS magnet system (MS) consists of two Y-Ba-Cu-O samples in the form of bulk cylindrical discs, which are encapsulated in an aluminium holder and wrapped with styrofoam. The aluminium holder is designed to locate the bulk HTS magnets on either side of the metal rod. After field cooling magnetisation with an applied field of 1.5 T at 77 K, the bulk HTS MS provides a quasi-permanent magnetic field over 240 s, enabling Lorentz force measurements to be carried out with a constant velocity of the metal rod. Two sets of Lorentz force measurements with copper and aluminium rods with velocities ranging from approximately 54-81 mm s-1 were performed. The obtained results, which are validated using a numerical model developed in COMSOL Multiphysics, demonstrate the linear relationship between the Lorentz force and velocity of the moving conductor. Finally, the potential of generating very high magnetic fields using bulk HTS that would enable LFV in even weakly-conducting and slow-flowing fluids, e.g., glass melts, is discussed.