Experimental Concept

How does Supax look like? What magnet will be used and how is the cavity design? How is the readout looking like?

Our Magnet System

The system which is currently under preparation at the University of Bonn is an integrated cryostat magnet system with a magnetic field strength of 12T that allows to operate a cavity at a temperature of 10mK. The magnetic field is provided by a superconducting solenoid magnet with a cylindrical magnetic volume with a diameter of 10 cm and a height of 25 cm.

Our preliminary tests are conducted at the Helmholtz Institute of Mainz in the laboratory of Prof. D. Budker, who kindly allows us to access a 14T magnet with a significantly smaller volume and an minimal operating temperature of 4L.

© Kristof Schmieden
Eine Wissenschaftlerin und ein Wissenschaftler arbeiten hinter einer Glasfassade und mischen Chemikalien mit Großgeräten.
© Kristof Schmieden

Our Cavity Design

SupAX will use cylindrical shaped cavities, which are operated at superconducting temperatures to reduce the noise level, thus increasing the signal sensitivity. The superconducting coating of the cavity will also improve its quality factor and increase therefore the probability of the conversion of an axion to a photon.

Clearly, the time of data-taking at one frequency improves the sensitivity on the gayy with a sqrt(t) dependency. In order to allow to test different frequencies and hence probe different mass points, the SuPAX concept foresees to split the cylindrical cavity in three parts, with two movable sides. This allows to probe simultaneously three different frequencies.

First tests of non-tunable, normal-conducting and superconducting cavity systems have been already performed.

Our Readout System

The tunable cavities will have several ports, which are connected via SMA cables. A weakly coupled antenna is used to inject signals from a Vector Network Analyser (VNA) via a 20 dB attenuator. The critically coupled antenna is connected to a switch where one output leads straight out of the cryostat and into the VNA while the other feeds into a cryogenic low noise amplifier (LNA) with 36 dB gain. The amplified signal is fed into a real-time spectrum analyser (RSA) with an internal SI25dB amplifier, outside the cryostat. The RSA is connected via a USB3 link to a dedicated readout PC and controlled via custom made software. A 10MHz window around the center frequency is read out by the RSA and sampled with 28 MS/s. The real-time IQ data is streamed from the device and converted via a FFT into the frequency domain with a readout band width of 1kHz. The actual search for axions is then based on the FFT data.

© Tim Schneemann
Eine Wissenschaftlerin und ein Wissenschaftler arbeiten hinter einer Glasfassade und mischen Chemikalien mit Großgeräten.
© IAXO Collaboration / Matthias Schott

Our Expected Sensitivity

We hope to probe QCD axion masses between 20-40ueV down to couplings for 10-14 GeV-1, hence reaching the famous QCD axion band as illustrated in the Figure. This would imply an overall data-taking time of over two years.

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