rf surface impedance of a two-gap superconductor, considering magnesium diboride for accelerator applications

TL;DR

This paper models the RF surface impedance of magnesium diboride (MgB2) as a two-gap superconductor using an extended BCS theory, providing insights into its suitability for accelerator applications.

Contribution

It introduces a two-band extension of BCS theory into Mattis-Bardeen theory to accurately predict MgB2's surface impedance for RF applications.

Findings

Numerical results align with experimental data.

Surface impedance is dominated by the smaller superconducting gap.

Utility of MgB2 is limited in the 10-20 K temperature range.

Abstract

In this paper, we apply the two-band extension [1] of BCS theory [2] into the Mattis-Bardeen theory [3] to obtain the surface impedance of a two-band superconductor, and apply it to magnesium diboride (MgB2) for radiofrequency (RF) superconductivity applications. The numerical results for MgB2 are in good agreement with the previously published experimental results [4]. The surface impedance properties are clearly dominated by the smaller gap, significantly limiting utility in the 10-20 K regime that might otherwise have been attractive.