Status and Early Results from the Axion Dark Matter eXperiment - High Frequency (ADMX-HF)

The axion was originally proposed as a solution to the Strong-CP problem of the Standard Model. A sufficiently light axion ($1-1000~ \mu$eV) also represents an excellent cold dark matter candidate. Such axions may be detected by their resonant conversion to photons in a high-$Q$ microwave cavity permeated by a strong magnetic field. Previous experiments have probed the first decade in mass using this method. ADMX-HF was designed and built as an innovation test-bed and a data pathfinder for the second decade in mass range. The experiment, initially configured with a 9-tesla magnet, dilution refrigerator, 2-liter tunable copper cavity, and a Josephson Parametric Amplifier, is now operational with a system noise temperature approximately twice the Standard Quantum Limit. Preliminary data in the $25~\mu$eV range (on the order of 6 GHz in resonant frequency) will be presented, as well as an overview of ongoing R\&D on new cavity and amplifier technologies that will be validated in situ within the next few years.