Search for 5–9 μeV Axions with ADMX Four-Cavity Array

An axion is a particle that could resolve some issues with strong interaction CP symmetry and dark matter. A tunable microwave cavity permeated by a strong external magnetic field can be used to detect axions. The Axion Dark Matter eXperiment (ADMX) has developed a four-cavity array design to explore the axion mass range of 5–9 μeV. Tuning of each cavity frequency is done primarily by a coarse tuning rod, with a fine tuning rod used to lock frequencies together. Aluminum prototypes at 1:3 scale have been built and tested. At 300 K, the TM010 frequency varied from 4.4 to 6.4 GHz and crossed three TE modes. Electroplating pure aluminum on the cavity improved the Q factor by 27%. Preliminary results from 4.2 K test showed a 2% reduction of resonant frequency and an improvement in Q by a factor of 2.7 compared to the 300 K values.