Task 6.1
Baseline concept of the RF system for acceleration to the High Energy Complex (HEC) (UROS)

This task, led by the University of Rostock, aims to provide a preliminary design concept for the SRF cavities for acceleration in the Rapid Cycling Synchrotrons (RCS) of the HEC of the muon collider. For the acceleration stage of the HEC, the short muon lifetime requires the highest possible acceleration rate to reach energy gains on the order of 10 GeV per turn. This is foreseen to be provided with very high voltage SRF cavities. A suitable cavity technology, including the accelerating cavity type and shape, the cavity material, and the main RF frequency, will be determined for this system. Strong transient beam loading effects, as well as strong wake field effects due to the very high intensity of the muon bunches will also have to be addressed in the cavity optimisation. In cooperation with WP5, a full set of parameters for the RF cavities that address longitudinal beam dynamics and stability will be established (R/Q, Vmax, …) for the fundamental mode and HOMs’ suppression. This will provide input specifications for the design concept of the RCSs cavities.

Task 6.2
Baseline concept of the RF system for the Muon Cooling Complex (MCC) (CEA and INFN)

The focus of this task, led in conjunction by CEA and INFN, is to lay out a conceptual design of the RF systems for the MCC, based on a consistent set of parameters for all RF cavities and associated systems to be integrated into the cooling cells of the MCC obtained from inputs given by WP4 and WP8. For the muon cooling section, one challenge already pointed out in the preliminary MAP study, is to achieve gradients of at least 30 MV/m in RF cavities that will be placed in magnetic fields of 13 T, and explore whether it is possible to push these values at the light of the latest developments in RF and magnet technology. At first, specifications for the design of all RF cavities will be collected (frequency, gradient, length, B-field, aperture). Then, based on the guidance given by WP4, full set of parameters for the cavities will be calculated, serving as a base for their conceptual design and integration in the cooling cells. The impact of beam loading on the muon energy spread will also be assessed at this stage and appropriate mitigating actions will be recommended.

Task 6.3
Breakdown mitigation studies for cavities of the muon cooling cells (CEA)

The goal of this task, led by CEA, is to study and enhance the present comprehension of the intrinsic concepts that influence the break down rate of RF cavities submitted to strong magnetic fields. We plan to extend existing theoretical studies, and with additional inputs from previous experimental studies at CERN for CLIC and FermiLab for MAP, as well as from additional tests performed in the scope of this task, realistic solutions to mitigate the breakdown and provide guidance for the design and the fabrication of high gradient RF cavities that stand strong magnetic fields in the MCC will be proposed.

Task 6.4
Baseline concept of high efficiency and high-power RF sources for the muon collider (ULA)

The aim of this task, led by University of Lancaster, is to provide a baseline concept for the RF sources needed for the muon collider that will require higher RF power than is currently possible with commercially available sources. Recent studies at CERN and Lancaster have shown that using novel two-stage klystrons can significantly increase their efficiency and thus reduce their power consumption. At first, the requirements in terms of frequencies, peak power and efficiency for all RF sources that provide RF to the muon collider cavities will be collected. Then, conceptual studies to improve by design the intrinsic energy efficiency of the most power-demanding RF sources in order to ensure sustainability over the long term will be presented.