Rybka, GrayBoutan, Christian Robert2017-05-162017-05-162017-05-162017-03Boutan_washington_0250E_16832.pdfhttp://hdl.handle.net/1773/38675Thesis (Ph.D.)--University of Washington, 2017-03The Axion is a well motivated hypothetical elementary particle that must exist in nature if the strong CP problem of QCD is explained by the spontaneous breaking of a Peccei-Quinn symmetry. Not only would the discovery of the axion solve deep issues in QCD, an axion with a mass of $\mu$eV - meV could account for most or all of the missing mass in our galaxy and finally reveal the composition of dark matter. The Axion Dark Matter experiment (ADMX) seeks to resolve these two critical problems in physics by looking for the resonant conversion of dark-matter axions to microwave photons in a strong magnetic field. Utilizing state of the art electronics and dilution refrigerator cryogenics, ADMX is the world's leading haloscope search for axions - able to discover or rule out even the most pessimistically coupled QCD axions. With multi-$TM_{0N0}$ functionality and with the commissioning of the new high-frequency Sidecar experiment, ADMX is also sensitive to a wide range of plausible axion masses. Here I motivate axions as ideal dark matter candidates, review techniques for detecting them and give a detailed description of the ADMX experiment. I discuss my contributions to the construction of the ADMX dual-channel receiver, which is the most sensitive microwave receiver on earth. I discuss the data acquisition, data taking and real-time analysis software. The primary focus of this work, however, is the ADMX Sidecar experiment which is a miniature axion haloscope that fits inside of the ADMX insert and has the capability of searching for axion masses between 16$\mu$eV - 24$\mu$eV on the $TM_{010}$ and 26.4 - 30$\mu$eV on the $TM_{020}$. I discuss analysis of the Sidecar data and exclude axion-to-two-photon coupling $g_{a\gamma \gamma} < 6\times 10^{-12} GeV^{-1}$ over a mass range of 3$\mu$eV ($\Delta f \sim$ 708 MHz) from 21.05 - 23.98 $\mu$eV for axions that compose 100$\%$ of dark matter. Over a narrow subsection of this range, 22.89 - 22.95$\mu$eV ($\sim$15 MHz) I set a stricter limit $g_{a\gamma \gamma} < 10^{-12} GeV^{-1}$.application/pdfen-USnonePhysicsPhysicsThesis