Updated transverse stability criteria for cavity HOMs in RCS

• David Amorim (EPFL)

Room: 17/1-007

Transverse impedance of the RF system

• Leonard Thiele (Rostock University (DE))

Room: 17/1-007

Discussion and AOB

• Simon Albright (CERN)
• Heiko Damerau (CERN)
• Elias Metral (CERN)
• Antoine Chance (CEA Irfu)
• Alexej Grudiev (CERN)
• David Amorim (EPFL)
• Fabian Batsch (CERN)
• Elleanor Lamb
• Lisa Soubirou
• Leonard Thiele (Rostock University (DE))

Room: 17/1-007

Follow-up points Room: 17/1-007 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? - *How do define a reasonable synchronous phase?* - First start for constant acceleration, then real ramps - *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 - *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)