ODU, Norfolk, Virginia, USA
We report extensive numerical simulations on nonlinear dynamics of a trapped elastic vortex under rf field, and its dependence on electron mean free path li. Our calculations of the field-dependent residual surface resistance Ri(H) take into account the vortex line tension, the linear Bardeen-Stephen viscous drag and random distributions of pinning centers. We showed that Ri(H) decreases significantly at small fields as the material gets dirtier while showing field independent behavior at higher fields for clean and dirty limit. At low frequencies Ri(H) increases smoothly with the field amplitude at small H and levels off at higher fields. The mean free path dependency of viscosity and pinning strength can result in a nonmonotonic mean free path dependence of Ri, which decreases with li at higher fields and weak pinning strength.
ODU, Norfolk, Virginia, USA
JLab, Newport News, Virginia, USA
ODU, Norfolk, Virginia, USA
JLab, Newport News, Virginia, USA
The SIS structure which consists of alternative thin layers of superconductors and insulators on a bulk niobium has been proposed to shield niobium cavity surface from high magnetic field and hence increase the accelerating gradient. The study of the behavior of multilayer super-conductors in an external magnetic field is essential to optimize their SRF performance. In this work we report the development of a simple and efficient technique to measure penetration of magnetic field into bulk, thin film and multilayer superconductors. Experimental setup contains a small superconducting solenoid which can produce a parallel surface magnetic field up to 0.5 T and Hall probes to detect penetrated magnetic field across the superconducting sample. This system was calibrated and used to study the effect of niobium sample thickness on the field of full magnetic flux penetration. We determined the optimum thickness of the niobium substrate to fabricate the multilayer structure for the measurements in our setup. This technique was used to measure penetration fields of Nb3Sn thin films and Nb3Sn/Al2O3 multi-layers deposited on Al2O3 wafers.
TUOFDV01
ODU, Norfolk, Virginia, USA
We address the nonlinear dynamics of penetration of vortices in a superconductor subject to a periodic magnetic field H(t)=H0\sinω t parallel to the surface. The time-dependent Ginzburg-Landau equations for a gapped superconductor were simulated numerically to calculate the frequency and temperature dependencies of the field onset Hp(T,ω) of vortex penetration at T≈ Tc. It is shown that Hp(T,ω) can exceed the dc superheating field Hs at which the Meissner state becomes unstable. Here Hp(T,ω) increases with ω and approaches √{2}Hs(T) at ωτ≥ 1, where τ(T) is the energy relaxation time of quasiparticles on phonons. We also investigated the effect of surface topographic defects on Hp(T,ω) and showed that they can substantially reduce Hp(T,ω) and cause additional power dissipation. Ultimately, we draw conclusions by comparing the results of our calculations with recent experimental measurements.