Abstract
This paper describes the experimental results for the rotational loss of a ring-shaped flywheel supported by high Tc superconducting levitation. Superconducting levitation is appropriate for rotating a ringshaped flywheel which has neither shaft nor hub because it is a noncontact and automatically stable levitation without any control systems. The rotational loss has been investigated using a smallscaled experimental machine consisting of 16 bulk superconductors 46mm in diameter and a ringshaped flywheel about 300mm in diameter. The rotational loss decreased as the levitation gap height increased. In lowspeed rotational regions, the rotational loss was in proportion to the rotation speed and depended more on the levitation gap. In highspeed rotational regions, the rotational loss was in proportion to the third power of the rotation speed and depended less on the levitation gap. The cubic rotational loss in He was reduced to onefifth of that in air. The magnetic field pinned in bulk superconductors induces a loss in the materials composing the ring-shaped flywheel. The rotational loss of a ringshaped flywheel supported by superconducting levitation can be reduced by improving the uniformity of the magnetic fields along the ring, enlargement of the bulk superconductor (s), and densely arranging the bulk superconductors.
