Notes from an informal meeting on the Muon Collider Lattice Design

Date: 25^th May 2023

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

Aim: Presentation of an updated version, taking comments from previous meetings into account, of the 10 TeV com muon collider, and feedback fot further studies.

Main points of the presentation and discussion:

• Changes compared to the latest version presented:
  • Optimization of phases of sextupole chromatic compensation sextupole pairs.  This allowed to reduce the dependance of the tunes from the momentum offset and to improve the off-momentum dynamic aperture.
  • Off-momentum dynamic aperture improved, but still smaller than requirements.
  • Residual dispersion at the IPs has been reduced to values with a neglibible impact on the luminosity.
  • Decrease of the Montague W functions after the IR and CC regions alone (handover to matching section). Nevertheless, the W functions at this handover to the matching section increased again after completing the lattice and rematching to have small W at the IP.
     
• Main points from the discussion
  • The working point of the lattice version presented, with tunes close to a half-integer and an integer resonance, is the result after connecting all pieces (IR, CC, matching section and arc) of the collider. Optimized choice of the working point for further iterations shoud improve dynamic apertures.
  • Optimization of β^* versus momentum offset δ instead of matching Montague W at the IP to zero. Some plots show of β^* versus momentum offset δ are asymmetric despite W matched to zero. Changing the strategy and accepting a (small) non-zero W would allow to improve. Increasing the number of data points (momentum offsets) of these plots will make the interpretation easier. 
  • Some discussion on difficulties of MAD-X matching routines to converge. To be checked whether insufficient number of iterations or another explanation can be identified.
  • Katsunobu suggested to check whether coherent synchrotron radiation may be an issue.
     
• Next steps
  • Working point adjustment and control. Improved working point optimization and and tuning range will be implemented for next version (possibly as additional task of longer matching section). This should as well improve the momentum acceptance.
    • Adding one more arc cell is proposed by Pantaleo as a simple way to move the working point to a more suitable region for a fast study.
    • Katsunoby proposes to adjust the phase at the handover to the arc.
  • Studies of non-linear behaviour of arc sells to separate the impact coming from different parts of the lattice.
  • Separation turn-by-turn phase space plots combining result for several particles (different initial horizontal and vertical positions and different momentum offsets) into several plots to ease the interpretation.
  • Check whether coherent synchrotron radiation may be a limitation.