A tunable higher-frequency resonant cavity for HAYSTAC*

HAYSTAC is a dark matter detector that looks for an axion-induced power excess spectrally coincident with the resonance of a microwave cavity immersed in a strong magnetic field. The current HAYSTAC cavity achieves frequency-tunability over the 3.6-5.8 GHz window via its single, off-center tuning rod. Probing higher frequencies, however, introduces unique challenges. In particular, smaller volumes, lower quality factors, and higher densities of intruder modes decrease sensitivity and increase operational complexity. Here, we present the design and initial testing results of a cavity using seven tuning rods for the frequency range 5.5-7.4 GHz. Our seven-rod design will allow HAYSTAC to probe higher axion masses while maintaining axion sensitivity significantly greater than that of the standard design.