Development of Iris-Connected Multicell Cavities for Axion Searches*

For relatively low axion mass ranges (< 4 μeV), a single cavity has been used for axion detection to reach the DFSZ limit. However, to scan at larger mass ranges, the cavity physical dimension will scale unfavorably down with frequency, necessitating the usage of multiple cavities to maintain the detection volume. Working with multiple cavities adds significant complexity to the detector because of the need to combine the output signal coherently from the multiple cavities. As an alternative, we propose a multicell cavity to face this challenge. Multicell cavities are routinely used and employed in particle accelerators. Using a similar concept for axion haloscope detectors is appealing. In this talk, we report on developing a 4-cell cavity in the frequency range 4.3-6.3 GHz. In this cavity, four cells of circular cross-section are connected with irises. In this case, the TM010-like mode resides collectively in the cavity's different cells, eliminating the need for coherent signal combination. It can be tuned with a conventional rotary mechanism to bring the frequency from 4.3 GHz, when the four rods at the side-walls, to 6.3 GHz when the four rods rotate to be in the center of each cavity. The proposed structure maintains the large tuning range of a circular cross-section cavity (35%) even with increasing the number of cells in the structure, which is advantageous compared to other multicell structures proposed before for axion searches in the literature.