13th meeting on HEMAC discussions

Tuesday 22 Nov 2022, 16:45 → 17:30 Europe/Zurich

Zoom

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

16:45 → 17:05 Preliminary considerations for the final-stage RCS in the LHC tunnel

Speakers: David Amorim (CERN), Fabian Batsch (CERN)

2022-11-22_HEMAC_genetic_algorithm.pdf

MC_HEMAC_FB_221122.pdf

17:05 → 17:20 Discussion

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?

• 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

• Average gradient of RF sections

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

• How do define a reasonable synchronous phase?

  • First start for constant acceleration, then real ramps

• Power in higher-order modes (HOMs)?

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

  • Mauro Migliorati? Presently no code can do it.
  • David has impedance model for ILC cavities

• Resistive wall impedance?

  • David, contact with JPARC, collecting information
  • Luca will organize a dedicated meeting on 24th November: muon collider magnet working group

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

Priority 2

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

• 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

• More detailed lattice model, beyond smooth approximation.

Further options

• FFA alternative for RCS?

17:20 → 17:30 Round table

Speakers: Alexej Grudiev (CERN), Antoine Chance (CEA Irfu), David Amorim (CERN), Elias Metral (CERN), Fabian Batsch (CERN), Heiko Damerau (CERN), Ivan Karpov (CERN)