The microwave cavity with the end cap removed showing the two tuning rods. The rods are used to adjust the cavity resonant frequency.
The magnitude of the electric field across the center section of the cavity for the TM010 mode (the mode most sensitive to axions) as the rods are moved.
The resonant frequency of the cavity as the rods move within the cavity.
The microwave cavity within the magnet bore is at the heart of ADMX. It is a circular cylinder, 1 meter long and 0.5 meter diameter. We search for axions by slowly scanning the cavity resonant frequency by adjusting positions of two tuning rods within the cavity. A signal appears when the cavity resonant frequency matches the axion mass.
The expected signal from axion decay is so small that the entire experiment is cooled to well below 4.2 degrees Kelvin with a liquid helium refrigerator to minimize thermal noise. The electric field within the cavity is sampled by a tiny antenna connected to an ultra-low-noise microwave receiver.