Update on resonator development for ALPHA

Next-generation axion haloscopes are in development to search for post-inflation QCD axions with masses in the 40-180 μeV range. Searching this theoretically well-motivated mass range requires new haloscope technology. Current haloscopes use resonant cavities to enhance the photon signal from converted axions. Heavier axion masses correspond to higher photon frequencies, making the use of a traditional resonant cavity difficult due to limitations in the signal power arising from the cavity's physical size. The signal power scales with volume, but volume unavoidably decreases as the cube of frequency in a resonant cavity. The ALPHA (Axion Longitudinal Plasma HAloscope) experiment solves this problem by replacing the traditional resonant cavity with a metamaterial resonator. The plasma frequency of the metamaterial is decoupled from its physical size, allowing the interaction volume to remain large at high frequencies. This talk will present progress in the development of a prototype metamaterial resonator for ALPHA as well as updates on supporting R&D.