MADMAX is preparing for a stopover at CERN from 2022. Mel Gibson, his artillery and quest for revenge will not be there, but instead a handful of physicists armed with an aged magnet will be searching for dark matter in CERN’s North Area (not to be confused with a post-apocalyptic wasteland).

Indeed, the MADMAX collaboration (MAgnetized Disks and Mirror Axion eXperiment, external to CERN), humbly proposes to identify the nature of dark matter and to solve the enigma of the absence of so-called charge-parity (CP) symmetry violation in the strong sector, while detecting a particle that has eluded physicists for decades: axions.

To do so, the collaboration has developed a brand-new concept using a booster composed of dielectric disks and mirrors. The booster acts as a resonator to amplify the photon flux that axions would produce under a magnetic field, if these axions exist. In order to validate the concept, a prototype needs to be tested under a magnetic field before the launch of the experiment, planned to be located at DESY in Germany.

Although such a magnetic field is difficult to obtain, the collaboration can rely on CERN's assistance. On 16 September, CERN's Research Board agreed that the MADMAX prototype could use an old magnet previously used by the ATLAS experiment. The “Morpurgo” magnet is located in the North Area and generates a field of up to 1.6 Tesla. It is one of the first superconducting magnets to be used at CERN. More than 40 years after the NA3 (North Area 3) experiment first used it in 1978, this sturdy magnet still tests ATLAS subdetectors. MADMAX physicists will jump in to mount and test their prototype during the inter-beam period, when ATLAS is not using the magnet. A solution that suits everyone: for MADMAX, a magnet that meets the prototype's criteria is provided free of charge, and for ATLAS, the space around the magnet is reorganised and optimised, which is necessary for the installation of the prototype.

The recycling and repurposing of equipment is common at CERN, in the spirit of pragmatism and sustainability. With successive generations of equipment, state-of-the-art accelerators go on to become injectors for their successors, and old magnets are reused for new experiments. This is the case, for example, with the CAST experiment, which uses an old LHC dipole prototype in its search for, once again, axions.

However, allowing external researchers to use CERN equipment, as in the case of MADMAX, is far from trivial. According to Pascal Pralavorio, the MADMAX contact person at CERN, this helps to develop new ideas: "Today, particle physicists are searching for new physics in many different directions, which naturally leads to experiments based on novel concepts. To validate them, we must make the most of the equipment that’s already available, and that is what MADMAX and CERN are doing with the Morpurgo magnet.”

CERN's endeavours to benefit science around the world have long been visible whether through collaborations, prototyping, donating equipment and more, and this is set to continue. Although we don’t need another hero, we wish the MADMAX researchers well in their quest for axions.