  We present results from the first experimental demonstration of a tunable
thin-shell axion haloscope. This novel geometry decouples the overall volume of
the cavity-based resonator from its resonant frequency, thereby evading the
steep sensitivity degradation at high-frequencies. An aluminum $2.6$ L ($41$
$\lambda^3$) prototype which tunes from $7.1$ to $8.0$ GHz was fabricated and
characterized at room temperature. An axion-sensitive, straightforwardly
tunable $\mathrm{TM}$$_{010}$ mode is clearly identified with a room
temperature quality factor, $Q$, of $\sim$$5,000$. The on-resonance $E$-field
distribution is mapped and found to agree with numerical calculations.
Anticipating future cryogenic operation, we develop an alignment protocol
relying only on rf measurements of the cavity, maintaining a form factor of
$0.57$ across the full tuning range. These measurements demonstrate the
feasibility of cavity-based haloscopes with operating volume $V\gg\lambda^3$.
We discuss plans for future development and the parameters required for a
thin-shell haloscope exploring the post-inflationary axion parameter space
($\sim$$4$ to $\sim$$30$ GHz) at DFSZ sensitivity.
