Dear colleagues,

As reported in the recent global timing working group report (EDMS D1097725), the BDS group was invited to look into ways to cut ~150m from the length of the positron system (optionally also from the electron side) to fix the timing mismatch between e- and e+ beams which exists in the current TDR lattices. There is a change request in process looking at increasing the linac length by ~1.5km (CR4 - EDMS D1092915) for additional reasons which will fix this problem if that is approved, but here Nick has also asked for a quick look into the possibility of shortening the BDS as an input into these discussions.
I think the most obvious candidate is for shortening the energy collimation system, which comes mainly at the cost of an additional 2.1% horizontal emittance growth and 220 MeV energy loss for the 1 TeV machine (negligible impact for 500 GeV).
As a suggested response to these requests, please find attached short note. Let me know if you have any comments or other suggestions on this topic.

Best regards,

- Glen.

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