40th meeting on HEMAC discussions

Friday 26 Jun 2026, 08:45 → 09:45 Europe/Zurich

6/R-012 - conference room (CERN)

https://cern.zoom.us/j/66586421590?pwd=TVZ4WEdtaDRQNFBkNitUTm4rTG83Zz09

08:45 → 08:55 Final MuCol report on muon collider

• Writing process and timeline
• Plan, work organization
• Final report due on 28/02/2027
  • Accelerator
  • Detector
• WP Final reports – Autumn 2026
  • Proton driver, Muon production, Collider Ring, High Energy Complex, RF sources, RF for cooling and high energy complex, Collider magnets, Cooling cell design

Speakers: Antoine Chance (CEA Irfu), Heiko Damerau (CERN)

2026_06_26_high_energy_deliverable.pdf

2026_06_26_high_energy_deliverable.pptx

08:55 → 09:05 Tracking studies

• Transverse

Speakers: Lisa Soubirou, Lisa Soubirou

09:05 → 09:15 Tracking studies

• Longitudinal

Speakers: Leonard Sebastian Thiele (University of Rostock), Leonard Thiele

09:15 → 09:44 Discussion and AOB

Speakers: Alexej Grudiev (CERN), Antoine Chance (CEA Irfu), David Amorim (EPFL), Elias Metral (CERN), Elleanor Lamb, Fabian Batsch (CERN), Heiko Damerau (CERN), Leonard Thiele, Lisa Soubirou, Simon Albright (CERN)

09:44 → 09:45 Follow-up points

Few open points for follow-up:

Priority 1

• Optimize losses in RCS chain for best overall performance, allowing different transmission in the two or three machines

  • Difficult with lots of degrees of freedom: straight-forward only for constant acceleration
  • Difficulty of different magnets (ramp rate)
  • How to distribute total RF length over different machines? Minimization of overall total voltage?

• Acceptable longitudinal emittance growth in the RCS chain and how to quantify it exactly?

  • Needs figure from low-energy acceleration (low energy), longitudinal emittance for colliders as a starting point. Criteria also on how much bunch is distorted. What is acceptable bunch shape deviation in the collider?
  • Currently assuming in the longitudinal plane 10% over full chain.

• How do define a reasonable synchronous phase?

  • First start for constant acceleration, then real ramps
  • Currently defined based on matching between RCS, could be optimised for power consumption?

• Average gradient of RF sections

  • 1.3 GHz: agreed 30 MV/m (conservative) and 45 MV/m (aggressive)
  • 800 MHz?

• Transient beam loading and counter-rotating bunches and multi-turn effects?

  • Avoid that counter-rotating bunches meet in RF section
  • Impact on placement of RF around the circumference?

• Longitudinal matching

  • How to generate the short bunch length required for the transfer into the collider ring?
  • Longitudinal matching of RCS with pre-acceleration stages (injection) and collider (ejection)

• Can the ILC cavity (possibly in a modified form) be used for the muon RCS?

  • Power in higher-order modes (HOMs) is potential show-stopper
  • Need refined paek and average power calculations for HOM couplers

• Resistive wall impedance?

  • David following chamber materials
  • Elleanor simulating for impact BD $Z_{||}$

• More detailed lattice model, beyond smooth approximation.

  • David developed a MAD-X lattice generator (from high-level machine parameters for muon RCS)

• Introduce chromaticity in transverse studies, do we need sextupoles?

Priority 2

• Cost functions per machine part: could one make an assumption for a cost per unit length of RF (plus some infrastructure cost offset per RF section), idem for unit length of magnets?

• Would two RCS be sufficient to accelerate from 60 GeV to 1.5 TeV?

  • Does not look very attractive

• Is transition gamma of ~20 a good number for the first RCS stage?

  • Check various transition gammas and their impact -> David to present

Further options

• FFA alternative for RCS?

Treated, at least in some detail

• What are the consequences if we want to use the LHC as the last accelerator ring?

  • Check consequences, check Shiltsev proposal: https://iopscience.iop.org/article/10.1088/1748-0221/13/10/T10003
  • 5 TeV cannot reached in the LHC tunnel

• Average gradient of RF sections

  • Agreed during collaboration workshops to keep two values: 30 MV/m (conservative) and 45 MV/m (aggressive)