Superconducting RF Cavities for the Axion Dark Matter eXperiment

The Axion Dark Matter eXperiment (ADMX) searches for Axions, a hypothetical dark matter candidate, through conversion to photons in a high magnetic field and are subsequently detected within a resonant cavity. The rate that this detector can scan potential axion masses (or photon frequency) depends linearly on the quality factor of the cavity. Though Superconducting Radio Frequency cavities (SRF) have been shown to have several orders of magnitude higher quality factor than copper, their quality factors typically degrade significantly in the high magnetic fields required for axion detection. Some type II superconductors have shown the potential for improved quality factors beyond that of copper even in magnetic fields ADMX would operate in. In this work, we present our progress on studying different materials at LLNL, primarily NbTi, Nb₃Sn and YBCO, using small test RF cavities with varying purpose-built geometries, that can operate in a Physical Properties Measurement System (PPMS), capable of fields up to 14 T and temperatures down to 2 K. Additionally, plans to conduct an axion search with a ‘hybrid’-SRF cavity as part of the ADMX sidecar will be presented. This work is being done as part of the design studies for the next phase of ADMX covering the 2-4 GHz range.