HALOX

Dark matter is one of the main puzzles in fundamental physics with rising interest from the scientific community and axions are among the best-motivated dark matter candidates. Their discovery requires to invent new challenging experimental techniques. Several proposals for novel experiments have emerged in the 2010 decade among which MADMAX is the only one sensitive to the mass range around 100 micro-eV, favored by the theory. It therefore gathers more and more attention since it was proposed in 2016. Today it is composed of about 50 scientists from 10 institutes from Germany (among which the Hamburg University and DESY), France (among which CPPM), US and Spain. Based on the novel concept of dielectric haloscope, MADMAX will feature a booster system consisting of 80 dielectric discs with more than a meter diameter which can be precisely positioned at cryogenic temperature and inside a 9 T magnetic field created by a superconducting dipole magnet with a large warm bore. Towards the realization of this demanding apparatus, the MADMAX collaboration has developed a staged approach of various prototypes to prove different aspects of the haloscope booster concept. The prototype detectors have been / will be operated in an existing magnet at CERN (1.6 T), thus allowing to perform searches for axion-like particles in an unexplored phase space. This will pave the road towards the final experiment, to be run at DESY-Hamburg, by concluding on the technological options. The goal of this proposal is to foster and reinforce the collaboration between the University of Hamburg, DESY and CPPM on the commissioning and exploitation of HALOX, a prototype of dielectric haloscope with three to six discs of 300 mm diameter. Operating it in a cryostat at liquid helium temperature will allow to perform an improved axion search. The reduced size prototype is a mandatory step to prove the technical feasibility of the project and to establish the production of all components. The competences of the German and French institutes are complementarity for the realization of HALOX. By strengthening this collaboration, the funding of this proposal would allow to increase the Franco/German visibility in the promising and uprising field of weakly-interacting dark matter searches. The synergy between the different teams is fostered around a common work program composed of different well identified tasks. The funding request of the project is developed over 3 years, dedicated to the commissioning and tests of the prototype (2025), its exploitation towards first physics results (2026) and its upgrade (2027). This ambitious and innovative project, with close connections between scientists and engineers of Hamburg University, DESY and CPPM, as well as possibilities for connections and exchanges of PhD students, offers a unique scientific potential coupled with several promising technological opportunities.