| Dipole (\textbf{left}) and solenoid (\textbf{right}) magnets with transversal and axial magnetic \mbox{fields, respectively.} |
| Dipole (\textbf{left}) and solenoid (\textbf{right}) magnets with transversal and axial magnetic \mbox{fields, respectively.} |
| Cavity (17.95 × 8.97 cross-section) spectrum around 8.4 GHz for $d=10a$ (blue) and $d=100a$ (red). {Simulation results from CST Studio Suite \cite{CST}.} |
| Rectangular irises for coupling between neighboring cavities: inductive (\textbf{left}) and capacitive (\textbf{right}). The pictures show the symmetric half of each one. |
| Rectangular irises for coupling between neighboring cavities: inductive (\textbf{left}) and capacitive (\textbf{right}). The pictures show the symmetric half of each one. |
| RADES 5-cavity haloscope: scheme and dimensions, and device before copper plating. |
| RADES 5-cavity haloscope: scheme and dimensions, and device before copper plating. |
| Electric field pattern (vertical polarization) for the five different configurations of mode $TE_{101}$ for the 5-cavity haloscope, with the associated form factors. The red fields denote positive levels, the green fields zero, and the blue fields negative. Taken and modified from \cite{Alvarez2018}. |
| Transmission coefficient magnitude at 2 K: simulated (black) and measured (green), where measurements include the effects of cables from and to the VNA. Taken and modified from \cite{Alvarez2018}. |
| Electric field pattern (vertical polarization) for the thirty different configurations of mode $TE_{101}$ for the all-inductive 30-cavites haloscope. Numbers on left side refer to the order of the configuration resonances with the frequency. {The red regions denote positive E-fields, and the blue regions negative ones.} |
| \textls[-15]{Simulated transmission coefficient magnitude of an all-inductive 30-cavity haloscope at 2 K.} |
| Electric field pattern (vertical polarization) for the thirty different configurations of mode $TE_{101}$ along the all-capacitive 30-cavites haloscope. Numbers on the left side refer to the order of the configuration resonances with the frequency. {The red regions denote positive E-fields, and the blue regions negative ones.} |
| \textls[-25]{Simulated transmission coefficient magnitude of an all-capacitive 30-cavity haloscope at 2 K.} |
| Manufactured 6cav and 30cav structures with alternated couplings. |
| Electric field pattern (vertical polarization) for the thirty different configurations of mode $TE_{101}$ for the alternating 30-cavites haloscope. Numbers on the left refer to the order of the configuration resonances with the frequency. {The red regions denote positive E-fields, and the blue regions negative ones.} |
| \textls[-15]{Simulated transmission coefficient magnitude of an alternating 30-cavity haloscope at 2 K.} |
| Measurement setup. The cavity was placed in the cold bore at near 2 K. The signal was amplified by a cryogenic LNA. Thermal contacts were employed to adapt the cryogenic and room temperatures for both the calibration and signal ports between flanges 1 and 2. |
| Block diagram of the analog acquisition module. |
| Block diagram of the digital acquisition module. |
| Removal procedure of the electronic background. (\textbf{a}): The initial raw spectra taken by the DAQ are combinations of electronic background, the cavity resonance peak, white noise, and a possible axion signal. The electronic background and cavity resonance were removed by (\textbf{b}): dividing the spectra at different LO frequencies and (\textbf{c},\textbf{d}): applying two SG filters. (\textbf{e}): The unit-less normalized spectra were combined into a grand unified spectrum. (\textbf{f}): The magnet-on and off grand unified spectra were subtracted to remove the systematic residual structure and create the final spectrum. Figures taken from \cite{Alvarez2021}. |
| Removal procedure of the electronic background. (\textbf{a}): The initial raw spectra taken by the DAQ are combinations of electronic background, the cavity resonance peak, white noise, and a possible axion signal. The electronic background and cavity resonance were removed by (\textbf{b}): dividing the spectra at different LO frequencies and (\textbf{c},\textbf{d}): applying two SG filters. (\textbf{e}): The unit-less normalized spectra were combined into a grand unified spectrum. (\textbf{f}): The magnet-on and off grand unified spectra were subtracted to remove the systematic residual structure and create the final spectrum. Figures taken from \cite{Alvarez2021}. |
| Removal procedure of the electronic background. (\textbf{a}): The initial raw spectra taken by the DAQ are combinations of electronic background, the cavity resonance peak, white noise, and a possible axion signal. The electronic background and cavity resonance were removed by (\textbf{b}): dividing the spectra at different LO frequencies and (\textbf{c},\textbf{d}): applying two SG filters. (\textbf{e}): The unit-less normalized spectra were combined into a grand unified spectrum. (\textbf{f}): The magnet-on and off grand unified spectra were subtracted to remove the systematic residual structure and create the final spectrum. Figures taken from \cite{Alvarez2021}. |
| Removal procedure of the electronic background. (\textbf{a}): The initial raw spectra taken by the DAQ are combinations of electronic background, the cavity resonance peak, white noise, and a possible axion signal. The electronic background and cavity resonance were removed by (\textbf{b}): dividing the spectra at different LO frequencies and (\textbf{c},\textbf{d}): applying two SG filters. (\textbf{e}): The unit-less normalized spectra were combined into a grand unified spectrum. (\textbf{f}): The magnet-on and off grand unified spectra were subtracted to remove the systematic residual structure and create the final spectrum. Figures taken from \cite{Alvarez2021}. |
| Removal procedure of the electronic background. (\textbf{a}): The initial raw spectra taken by the DAQ are combinations of electronic background, the cavity resonance peak, white noise, and a possible axion signal. The electronic background and cavity resonance were removed by (\textbf{b}): dividing the spectra at different LO frequencies and (\textbf{c},\textbf{d}): applying two SG filters. (\textbf{e}): The unit-less normalized spectra were combined into a grand unified spectrum. (\textbf{f}): The magnet-on and off grand unified spectra were subtracted to remove the systematic residual structure and create the final spectrum. Figures taken from \cite{Alvarez2021}. |
| Removal procedure of the electronic background. (\textbf{a}): The initial raw spectra taken by the DAQ are combinations of electronic background, the cavity resonance peak, white noise, and a possible axion signal. The electronic background and cavity resonance were removed by (\textbf{b}): dividing the spectra at different LO frequencies and (\textbf{c},\textbf{d}): applying two SG filters. (\textbf{e}): The unit-less normalized spectra were combined into a grand unified spectrum. (\textbf{f}): The magnet-on and off grand unified spectra were subtracted to remove the systematic residual structure and create the final spectrum. Figures taken from \cite{Alvarez2021}. |
| Axion--photon coupling vs. axion mass phase-space. In red is the CAST-RADES axion--photon coupling exclusion limit compared to other haloscope results and the CAST solar axion results. Inset: Zoom-in of the parameter range probed in the first CAST-RADES results (\mbox{$34.6738~\upmu$eV$ < m_a < 34.6771~\upmu$eV}), where the green region represents the uncertainty of the measurement. Figure taken from \cite{Alvarez2021}. |