Q.41:Linac Lattice – Focusing (on behalf of WG1)

1. Q.41:Linac Lattice – Focusing (on behalf of WG1) • Conservative choice: TESLA spacing of 24 cavities per quad • Most thoroughly studied (working lattices exist) • Cryomodules of 8 or 12 cavities OK • Split-tune (75/60 or more) provides protection against mode-rotation LRWFs • Cost saving options: • High energy part of the Linac is more robust (smaller emittance dilution) and larger quad spacing here is cost saving • Weaker focusing even in low-energy end : Hints that smaller emittance growth possible – studies ongoing • Depends on several factors: • Achievable cavity alignment to cryomodules • Presence or absence of HOM BPMs and cryomodules movers • Different steering/tuning algorithms (1:1, DFS, BA, Kobu’s method) were demonstrated • need more understanding of possible limitations • benchmarking among diff. codes. • Would like Quads to be separated from RF cavities • Optimize quad cryostat for better vibration suppression • Separate mechanical alignment of quad cryostats and cryomodules will improve achievable emittance growth, especially if cryomodules have movers