Speaker
Description
Haloscopes are sensitive detectors used for dark matter axion search in the microwave energy range. They rely on the axion to photon conversion in a static magnetic field, and its amplification by resonance with a cavity electromagnetic mode. While simple cylinder cavities working below below 1 GHz can provide large volume detectors of typically a hundred liters or more (GrAHal-CAPP), searches at higher frequencies are plagued by the decrease of the cavity volume, hence of the detector sensitivity. Several strategies can be used to increase the mode frequency without a detrimental loss of volume, like using multiple (ADMX), meta-material filled (ALPHA) or dielectric (MADMAX) cavities. In each case the mode frequency tuning, necessary to scan broad axion mass ranges, is challenging.
In this contribution we report on the investigation of mode tuning by filling a cavity with liquid He at 4K. Applied to a simple cylinder cavity with its TM010 mode resonating close to 6 GHz, the dielectric constant of the liquid allows to tune the mode frequency over 120 MHz. We simulate and measure the mode localization induced by the non-homogeneity of the dielectric constant in the cavity during the filling. We show that a very good mode stability and controlled slow filling can be achieved. As an illustration, the results of an axion search in the 6,23-6,33 GHz range are presented. Finally, we discuss how the mode localization can be mitigated, and the new method used for more complex cavity designs and at lower temperatures using superfluid He.
| Secondary track | T11 - Detectors |
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