The 3 Cavity Prototypes of RADES: An Axion Detector Using Microwave Filters at CAST

Abstract

The Relic Axion Detector Experimental Setup (RADES) is an axion search project that uses a microwave filter as resonator for Dark Matter conversion. The main focus of this publication is the description of the 3 different cavity prototypes of RADES. The result of the first tests of one of the prototypes is also presented. The filters consist of 5 or 6 stainless steel sub-cavities joined by rectangular irises. The size of the sub-cavities determines the working frequency, the amount of subcavities determine the working volume. The first cavity prototype was built in 2017 to work at a frequency of ∼ 8.4 GHz and it was placed at the 9 T CAST dipole magnet at CERN. Two more prototypes were designed and built in 2018. The aim of the new designs is to find and test the best cavity geometry in order to scale up in volume and to introduce an effective tuning mechanism. Our results demonstrate the promising potential of this type of filter to reach QCD axion sensitivity at X-Band frequencies.

On the Development of New Tuning and Inter-Coupling Techniques Using Ferroelectric Materials in the Detection of Dark Matter Axions

“…On the other hand, the CAST-CAPP/IBS group uses two movable dielectric sapphire plates placed in parallel and symmetrically at the cavity sides [14]. Also the RADES group has studied a mechanical tuning mechanism based on splitting the haloscope in two identical halves which can be moved symmetrically to increase the effective width dimension of the cavities, thus modifying the axion frequency search range [15].…”

Conceptual design of BabyIAXO, the intermediate stage towards the International Axion Observatory

“…From left to right: first 5 sub-cavities structure with inductive couplings (non-tunable, used in data-taking 2018 in CAST), alternating inductive-and capacitive-irises sub-cavities structure (non-tunable, used for proof-of-principle of behavior of alternating cavity types), 5 sub-cavities vertical cut structure (tunable, used for cryogenic measurements for the proof-of-principle of tuning), alternating 30cavities structure (non-tunable, used in data-taking 2020 in CAST). The first three structures are each about 15 cm long, the 4th one is of about 1 m length, see [126,129,130] for details. strategies in this direction are being explored.…”

“…The design challenge here in going to long structures is to well separate the mode coupling to the axions from other modes in such microwave filters. Recent progress on design advances and the construction of a 1-m-long filter structure, as well as first steps towards a tuning system through splitting the cavities in two halves are detailed in [129] and [130], respectively. Some of these developments are performed by groups belonging to the IAXO collaboration, with the long-term goal to assess the possibility of (Baby)IAXO hosting a multitude of such rectangular cavities.…”

Conceptual Design of BabyIAXO, the intermediate stage towards the International Axion Observatory

“…The design challenge here in going to long structures is to well separate the mode coupling to the axions from other modes in such microwave filters. Recent progress on design advances and the construction of a 1-m-long filter structure, as well as first steps towards a tuning system through splitting the cavities in two halves are detailed in [126] and [127], respectively. Some of these developments are performed by groups belonging to the IAXO collaboration, with the long-term goal to assess the possibility of (Baby)IAXO hosting a multitude of such rectangular cavities.…”

“…RADES cavities (stainless steel with copper coating) resonating around 8-9 GHz.From left to right: first 5 sub-cavities structure with inductive couplings (non-tunable, used in data-taking 2018 in CAST), alternating inductive-and capacitive-irises sub-cavities structure (nontunable, used for proof-of-principle of behavior of alternating cavity types), 5 sub-cavities vertical cut structure (tunable, used for cryogenic measurements for the proof-of-principle of tuning), alternating 30-cavities structure (non-tunable, used in data-taking 2020 in CAST). The first three structures are each about 15 cm long, the 4th one is of about 1 m length, see[123,126,127] for details.…”