20 May 2026

Photo: UHH/Krieger

Research team with the MADMAX cryostat.

Photo: UHH/Krieger

The MADMAX cryostat during construction.

Researchers at the Cluster of Excellence Quantum Universe have reached a critical milestone in the search for dark matter: The MADMAX cryostat has been successfully cooled down to just above 4 kelvin (minus 269°C), clearing the way for the experiment to move to CERN and begin searching for a particle that could explain one of the biggest mysteries in physics.

What are axions—and why do we want to find them?

Around 27% of the universe is made up of dark matter—a substance we know exists because of its gravitational effects on galaxies but which has never been directly detected. One of the most promising candidates is the axion, a particle first predicted in the 1970s. Despite decades of searching, no one has yet found one. Only now are experiments becoming sensitive enough to have a realistic chance of detection.

What is MADMAX?

MADMAX (short for Magnetised Disc and Mirror Axion Experiment) is a novel approach to axion detection. The principle: if axions exist as dark matter, they should be all around us. MADMAX aims to convert these axions into photons, which can then be detected.

To do this, the experiment uses a "dielectric booster"—a stack of ultimately up to 80 precisely arranged disks, each around one metre in diameter, placed inside an extraordinarily powerful dipole magnetic field of approximately 9 tesla. For comparison, an MRI scanner operates at around 1.5 to 3 tesla, and no magnet of this type and size has ever been built before. At each boundary surface between the disks, axions can be converted into photons; by spacing the disks at the right distances, the effect can even be amplified.

To detect these tiny signals, the entire setup must be kept at around 4 kelvin, also called cryogenic temperatures, to minimise background noise from thermal radiation.

To demonstrate that MADMAX is feasible, especially the in-situ reconfiguration of the dielectric booster by precisely moving individual disks at cold temperatures, a prototype booster has been built. This prototype booster will feature up to 20 disks with 30 cm diameter each. Of course, also this MADMAX prototype has to be operated at cryogenic temperatures, and that's where the MADMAX cryostat comes in.

Hamburg's contribution: The Cryostat

The cryostat, which is a highly specialised enclosure that maintains cryogenic temperatures, is Quantum Universe’s central contribution to the MADMAX collaboration and one of the largest pieces of equipment ever funded through the DFG's Großgeräteförderung program. Designed and built by a German engineering company to unique specifications, it features a novel double-walled vacuum vessel that allows the disks inside to be cooled via helium gas—a technically demanding solution with no standard blueprint to follow.

Led by Christoph Krieger, senior scientist in the group of Erika Garutti and key researcher at Quantum Universe, the team has been working on understanding and detecting dark matter since 2018. The cooldown process itself—bringing over 600 kg of stainless steel from room temperature down to near absolute zero—takes around three weeks, with a cycle turnaround time of six to seven weeks if any modifications are needed. After previous attempts revealed technical issues, including an internal cold leak that required repair, the successful cooldown in spring 2026 marks a hard-won and significant achievement.

DESY provided crucial support throughout the project, particularly through cryostat expert Jörn Schaffran, while the Max Planck Institute for Physics in Munich supplied the vacuum system.

What comes next?

With the cryostat now proven to work, the collaboration will begin assembling the full experiment, including the installation of the dielectric booster, the antenna, and the receiver system. Once commissioned in Hamburg, the plan is to transport the entire setup to CERN, where it will be placed inside a superconducting magnet for the first full axion search run.

As Christoph Krieger puts it, "The ultimate goal for MADMAX is to be able to search for axion dark matter in a part of the parameter space which was not really accessible before. And of course, if it exists, we want to find it."