Notes from an informal meeting on the Muon Collider Lattice Design

Date: 18^th November 2022

Present: C. Carli, K. Oide, P. Raimondi, D. Schulte, R. Tomas, K. Skoufaris

Aim: Presentation of ideas and existing designs for a 10 TeV com machine to experts on challenging collider lattices and get feedback on improvements and further studies to hopefully come to a working proposal

Main points of the discussion:

• Fringe fields, in particular of low beta quadrupoles, may seriously impact the dynamic aperture and compromise performance. Related effects may be a limitation to the maximum L^*. Fringe field effects have not been considered, but this is planned once a working lattice is available.
  • Proposal to increase the number of quadrupoles (four or five quadrupoles instead of triplet) of the low beta section. This might help with fringe field effects, but leads to longer IR.
• Discussion on dependence of tunes from action variables: a plot of tunes versus action variables will be generated
  • The results should give indications on suitable choices of the working point
  • Minimization of the dependence of the tunes from action variable should be done
• Discussions on phase advance between sextupole pairs
  • Suggestion to search for optics with phase advance of exactly π between sextupole pairs. This implies using more quadrupoles. Solutions with vertical phase advance close to zero are not compatible with these scheme and can be replaced by phase advance π as well in vertical.
• Solenoid of the detector: not taken into account so far for lattice design; hard edge model used for Beam Induced Background (BIB) simulations (info from FLUKA team after meeting).
• Discussion on cancellation of perturbations from sextupoles between chromatic compensation left and right of the IP (about π phase advance over IP plus typically multiples of π in chromatic compensation section)
  • Could help to reduce perturbations due to sextupoles and increase the dynamic aperture
  • Phase space deformations (e.g. plot on pages 16 and 17) at the IP (between the strong sextupoles) may be interpreted as confirmation of the effect.
  • To be further investigated. 
• Physical rms emittance is about 0.5 nm (25 um normalized rms emittance divided by relativistic gamma of about 47 000).