Superconducting Cavity Development for ADMX

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 is able to 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 the magnetic fields ADMX would operate in. In this work, we present our progress on studying these different materials at LLNL, primarily NbTi, using small RF cavities with varying purpose-built geometries, operating in fields up to 14 T and temperatures down to 2 K. A new analysis technique for in situ measurement of RF surface resistance of cavity sub-surfaces will also be presented. This work is being done as part of the design studies for the ADMX-Extended Frequency Range program covering the 2-4 GHz range.