  Most search experiments sensitive to quantum chromodynamics (QCD) axion dark
matter benefit from microwave cavities, as electromagnetic resonators, that
enhance the detectable axion signal power and thus the experimental sensitivity
drastically. As the possible axion mass spans multiple orders of magnitude,
microwave cavities must be tunable and it is desirable for the cavity to have a
tunable frequency range that is as wide as possible. Since the tunable
frequency range generally increases as the dimension of the conductor tuning
rod increases for a given cylindrical conductor cavity system, we developed a
cavity system with a large dimensional tuning rod in order to increase this.
We, for the first time, employed not only a piezoelectric motor, but also gears
to drive a large and accordingly heavy tuning rod, where such a combination to
increase driving power can be adopted for extreme environments as is the case
for axion dark matter experiments: cryogenic, high-magnetic-field, and high
vacuum. Thanks to such higher power derived from the piezoelectric motor and
gear combination, we realized a wideband tunable cavity whose frequency range
is about 42\% of the central resonant frequency of the cavity, without
sacrificing the experimental sensitivity too much.
