MgB2 Thin Films on Metal Substrates for Superconducting RF Cavity Applications

Abstract

Magnesium diboride is a promising material for superconducting RF (SRF) cavity applications. Compared to the currently used superconductor for SRF cavities Nb, MgB2 has the potential to achieve lower RF loss and higher acceleration field due to its higher critical temperature and thermodynamic critical magnetic field. Since the RF field only penetrates a few penetration depths into a superconductor, a superconducting coating of several hundred nanometers on a metal cavity is sufficient for superb SRF cavity performances. In this work, we report the properties of MgB2 thin films deposited by the hybrid physical–chemical vapor deposition (HPCVD) technique on different metal substrates including Nb, Mo, Ta, and stainless steel. All the films were polycrystalline, as indicated by X-ray diffractometry and scanning electron microscopy, and showed Tc∼39 K, determined by resistance versus temperature, magnetic susceptibility, and dielectric resonator measurements. MgB2 films deposited on Nb substrates polished to various degrees of smoothness exhibit similar Tc. The result is a promising step in the investigation of using MgB2 as an alternative to Nb for SRF cavities.