Switching speed for controlled damping using thin film YBa2Cu3O7-delta

The yttrium barium copper oxide (YBCO) high-T-c superconductor has a sharp dissipation peak at the magnetic flux phase transformation temperature, whether in the form of a single crystal, ceramic, or thin film. This peak has been proposed as the basis for a controlled damping system: if a magnet is attached to a mechanical oscillator and a fixed YBCO element is placed close to the magnet, then switching the temperature of the YBCO element from above the phase transformation temperature to the phase transformation temperature can be used to reduce the resonance Q of the mechanical oscillator by two or more orders of magnitude. It is demonstrated that, for a thin-film element, the damping can be switched on in less than 1 s; this time is limited by the thermal time constant of the YBCO element. The time to switch off the damping is governed by both the thermal time constant and the mechanical time constant of the undamped oscillator, tau = Q/pi v(0). (C) 1997 Published by Elsevier Science Limited.