Browsing by Subject "Cavities"

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    Superconductivity in high-frequency fields
    (Overseas Publishers Association, 1998-01-15) Kulik, I. A.
    Fundamentals of BCS and GLAG theories of superconductivity are reviewed with a focus on high.;,frequency properties of bulk superconductors, superconducting films and superconducting cavities. Superconductivity as a macroscopic quantum coherent state. Supercurrents and persistent currents. Condensate and excitations. Complex penetration depth and RF losses. Mechanisms of Q degradation in superconducting cavities at increasing a.c. field amplitude. Depairing effects and vortex nucleation mechanisms. Surface superconductivity and tilted vortices. Material parameters and factors responsible for ultimate performance of superconducting resonators.
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    ItemOpen Access
    Theory of Q-degradation and nonlinear effects in Nb-coated superconducting cavities
    (Gordon and Breach - Harwood Academic, 1998) Kulik, I. A.; Palmieri, V.
    Amplitude-dependent absorption of RF power in superconducting cavity with a wall of normal metal (Cu ) covered by a film of superconductor (Nb ) is determined by three factors: (1)depairing effect of high-current density on superconducting energy gap; (2)increase of electromagnetic power penetrating to normal metal and Drude-absorbed in it, at higher RF amplitude; (3)heating of both superconducting coating and normal substrate resulting in increase of quasiparticle excitation density at higher RF power (P). Cavity Q-factor is calculated as a hnction of RF amplitude A = fi and is shown to follow a relationship 1n(Q/ Q,) = -const-P" with a=l at low temperature T < T* and a=1/2 at T > T* where T* is characteristic temperature T* X TcS I d, S is the London penetration depth and d the thickness of superconducting coating.