Mapping the path toward a Muon Cooling Demonstrator

The Muon Cooling Demonstrator Workshop, held in Milan from 5 to 7 November and hosted in hybrid format, gathered around 90 participants from Europe, the US and Asia to take stock of the progress toward demonstrating ionisation cooling – the central challenge for the future Muon Collider.

The meeting, organised under the EU MuCol design study, brought together accelerator physicists, magnet experts, RF engineers and detector developers. It offered a detailed view of the technical work now converging into a coherent plan for the first cooling cell prototype.

Strong news from the IMCC collaboration opened the workshop: the group has surpassed its design goal for a muon cooling lattice. “Compared to the previous design, we not only met our core goal of a working muon cooling lattice, we over-fulfilled it,” said study leader Daniel Schulte (CERN). The new design improves on the IMCC’s target by a factor three in longitudinal emittance, simplifying downstream systems and marking a significant step toward a viable cooling channel.

Marco Statera (INFN LASA) presented the roadmap to bring the technology to TRL 6, ready for industrialisation, with high-temperature superconducting (HTS) coils, RF systems and lithium-hydride absorbers all advancing toward test-ready prototypes. “Funding R&D and device construction is crucial for technology development,” he noted, stressing the close synergy with the High Field Magnet programme.

Building on that foundation, Lucio Rossi (University of Milan and INFN LASA) outlined the project plan for the first cooling module, which integrates magnet, RF and absorber technologies into a single system. Drawing parallels with the HL-LHC IT String, he described the demonstrator as a bridge from component-level R&D to full-scale testing.

Several talks showcased the breadth of research feeding into the demonstrator. Giuseppe Scarantino (INFN LASA) presented the B5-like magnet design, using high-temperature superconductors cooled to 20 K to achieve higher fields in a compact geometry while cutting cryogenic power needs. Mattia Castoldi (INFN LASA) described the mechanical design of the cooling cell, where precision supports, and modular cryostats ensure alignment and stability under large magnetic forces.

Dario Giove (INFN LASA) complemented these talks with an update on the RF cavity design. He showed progress on the 704 MHz copper cavities with large apertures and thin metallic windows, outlining how thermal loads, Lorentz forces and mechanical stability shape the final geometry. A first integrated model of a three cell prototype was presented, including cooling channels, waveguide interfaces and replaceable window mounts, providing the basis for the upcoming fabrication and testing phase.

Other contributions addressed enabling technologies. José Ferreira Somoza (CERN) discussed remote-handling interconnections that could simplify assembly in tight cryogenic spaces, while Cristian Galimberti (CERN) outlined compact cryogenic solutions using cryocoolers and turbo-Brayton systems to operate magnets at 20 K without a full helium plant.

Beam and RF systems were another focal point. Alexander Spelling (Lancaster University, Cockcroft Institute and CERN) presented the RF power concept: each station must deliver 24 MW peak power at 704 MHz when feeding eight cavities, driving the need for new high-efficiency multi-beam klystrons. Complementary test stands at SLAC and INFN LASA, introduced by Muhammad Shumail (SLAC), will explore RF performance under magnetic fields up to 5 T.

Talks by Davide Zuliani (INFN Padova) and Rohan Kamath (Imperial College London) addressed beam diagnostics and commissioning, while Donatella Lucchesi (INFN Padova) highlighted the broader scientific reach of the demonstrator: “The Muon Collider demonstrator is a platform for groundbreaking physics discoveries, not just a step toward a collider.”

The siting of a future demonstrator also featured prominently. Tianhuan Luo (LBNL), presenting work by Diktys Stratakis (Fermilab), discussed options for hosting it at Fermilab, where existing proton infrastructure and space at the Muon Campus offer clear advantages. Javier Fernández Roncal (CERN) and Paul-Bogdan Jurj (Imperial College London) detailed a parallel study assessing how the former CTF3 facility at CERN could be repurposed as an alternative host site.

Closing the meeting, the collaboration reaffirmed the goal of constructing a full technology demonstrator by the end of the decade, integrating magnet, RF, cryogenic and vacuum systems into an operational test cell.

The workshop confirmed that muon cooling – once a theoretical milestone – is steadily advancing toward hardware reality. With design goals exceeded and international collaborations strengthening, the Muon Cooling Demonstrator is poised to become a cornerstone for future collider R&D.