Abstract
The improvement of the performance of RF superconducting cavities has recently motivated a considerable research effort in order to elucidate the effect of trapped magnetic flux on the surface resistance $R_{s}$. In this paper we show that by introducing a non-linear pinning force in the Gittleman-Rosenblum equations for the RF power dissipation due to a trapped magnetic flux in a superconductor, we can empirically describe the linear dependence on the RF field amplitude $B_{rf0}$ of the additional surface resistance $R_{fl}$. We also show that the proportionality between the RF-field dependent and independent terms $R_{fl}^{1}$ and $R_{fl}^{0}$, and the frequency dependence of $R_{fl}^{1}$ follow naturally from this approach.
Highlights
The quest for optimizing energy consumption in particle accelerators is motivating the research for increasing the quality factor in superconducting radio-frequency (SRF) cavities, as underlined in recent projects [1,2]
The original Gittleman and Rosenblum (GR) model considers a thin slab with uniform rf currents in its thickness d and small displacements of a rigid vortex lattice due to the small applied rf current compared to the critical current
The model presented in the previous section predicts a linear dependence of the flux sensitivity S 1⁄4 Rfl=B0 on the amplitude of the rf field Brf0
Summary
The quest for optimizing energy consumption in particle accelerators is motivating the research for increasing the quality factor in superconducting radio-frequency (SRF) cavities, as underlined in recent projects [1,2]. This in turn has motivated a renewed interest in several laboratories to study the effect of a trapped magnetic flux on SRF cavity performance and on the possibilities of minimizing its consequences. The effect of a trapped magnetic flux on the quality factor Q 1⁄4 Γ=Rs, where Rs is the surface resistance and Γ depends only on the cavity geometry, has been experimentally identified and studied since the earliest developments of SRF cavities [3,4,5]. We will show that the available experimental data on the frequency dependence of R1fl can be well described by our model
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