WP4: Muon Production & Cooling


The target and ionisation cooling work package will develop the muon source from the proton target through to the beginning of the acceleration system. A principle challenge for the muon collider is to deliver a beam having suitable luminosity so that the probability of a collision at the detector is significant. This WP will study the specific issues generated by the impact of a high brightness proton beam on a solid, liquid or fluidised powder target. It will then advance the understanding of the Ionisation cooling technique, whose principle has been recently demonstrated by the Muon Ionisation Cooling Experiment (MICE) collaboration, and design a configuration capable of delivering a muon beam compressed into a minimum phase-speace volume, such as to satisfy the requirements in terms of luminosity production at the experiements. WP4 will explore the technologies necessary to cool the beam in collaboration with WP6, WP7 and WP8, and will provide specificatins and input to WP3 and WP5. This WP will be led by UKRI, that will bring in its experience gained within the MICE collaboration. Other participants are Imperial, UWAR, CERN, INFN, UMIL, ENEA.


The muon cooling work package aims to establish a baseline for the muon target and cooling system in the light of known technological limits and identify areas where further R&D is required to deliver a satisfactory system conceptual design.


Task 4.1
Cooling system development (UKRI)

The cooling system uses a system of magnets, RF cavities and energy absorbing materials, to compress the beam both transverse and parallel to the direction of travel of the muon beam. This key system has to deliver a compression in the phase-space volume occupied by the beam by five orders of magnitude. A preliminary design for such a cooling system was developed within the MAP, assuming solenoids limited to 13 T and RF cavities limited to 30 MV/m. Subsequent experimental work demonstrated RF cavities having fields up to 50 MV/m, while exposed to significant magnetic fields. In collaboration with WP6 and WP7, the lattice optimisation will be extended to include these new parameter sets. The lattices will be made more realistic, with appropriate consideration of space for alignment equipment, beam instrumentation and due consideration of requirements for the magnet and RF system, also in liaison with WP6 and 7. The lattices will be assessed for integration into a cooling test, in close collaboration with WP8. Appropriate interfaces with the surrounding accelerator subsystems will be considered.

Task 4.2
Target system development (CERN)

In order to reach high luminosity, a high muon beam current must be delivered into the cooling system. This is achieved by impacting high energy protons onto a target, where pions are created and collected in a high field solenoid or a magnetic horn system. The pions decay to muons and are then delivered into the cooling systems. The proton beam proposed would be one of the highest power proton beams delivered. The proton beam pulse is proposed to be extremely short so that the resultant pion beam is also as short as possible. This would make the instantaneous proton power orders of magnitude higher than the state of the art. In this work package the impact of such a beam on the target systems and supporting infrastructure will be investigated. The pion yield will be assessed. The impact of the beam on target lifetime will be considered and mitigating strategies such as novel target concepts will be assessed. The heat load on the surrounding magnets will be studied and, in close collaboration with the Magnets WP7, the required shielding and associated magnet aperture requirements for the capture of pions will be studied.

Task 4.3
Code development (Imperial)

The BDSIM code has been developed in Europe in order to enable simulation of accelerator equipment in the presence of beam intersecting devices. BDSIM has been used to study several major proposed accelerator facilities including FCC-hh, CLIC and the ILC. BDSIM provides a unique combination of accelerator-style mapping techniques and particle physics-style tracking based on the Geant4 physics library. Previous simulations of ionisation cooling have been performed using G4Beamline, developed in the US. However G4Beamline has not been updated for more than 2 years despite a number of issues in the code. Imperial College, London will develop BDSIM in close collaboration with the BDSIM project leaders at Royal Holloway University of London so that it is fully integrated and capable of delivering simulations of the full cooling system.