'Electromaglev' ('Active-Magiev') - Magnetic levitation of a superconducting disk with a DC field generated by electromagnets: Part 2 Theoretical and experimental results on lift-to-weight ratio and lateral stiffness

We present Part 2 results of a comprehensive study, both theoretical and experimental, of an electromaglev ('active-maglev') system, in which a YBCO bulk sample is levitated stably in a DC magnetic field generated by a magnet system located underneath the floating sample. The 0th-order theory presented in Part 1 is used to interpret experimental results of levitation stability, lift-to-weight ratio, and lateral stiffness for four YBCO samples: 1) disk; 2) annulus; 3) the same annulus with a permanent magnet disk placed in the hole; and 4) ring. Also presented is a procedure to induce in a sample a trapped flux that is shown experimentally to be essential for the sample to levitate tilt-free. Trapped flux is another requirement for levitation stablity; it is in addition to at least two degrees of freedom required on spatial supercurrent flow and certain spatial profiles imposed on the field generated by the magnet system.