Working Group 3 Summary M. Sullivan / Y. Funakoshi

We had 6 sessions and 14 talks – 3 sessions were joint (WG2 and WG4) Fri. – Oct. 10 – CEPC IR Optics, Y. Wang (IHEP) – Status of FCC-ee interaction region design, R. Martin (CERN) – Crab waist interaction region, A. Bogomyagkov (BINP) – SuperKEKB background simulations, H. Nakayama (KEK) – Beam-beam limit vs. number of IPs and Energy II: scaling law, M. Xiao (IHEP) – Beam-beam limit vs. number of IPs and Energy I: beam- beam simulation, K. Ohmi (KEK) – Long-Range beam-beam interaction with the CESR bunch train operation, D. Rice (Cornell U.)

Sessions 4-6 Sat. – Fri Oct. 10 – Choice of L* I and SR in the HF IR, M. Sullivan (SLAC) – Choice of L* II: IR optics and dynamic aperture, E. Levichev (BINP) – Choice of L* III: requirement from the detector, G. Li – Lost particles in the IR and Touschek effects, M. Boscolo (INFN-LNF) – Infrared synchrotron methods and systems for monitoring and controlling particle beams in real time, M. Maltseva (TENZOR) – Detector beam background simulations for CEPC, H. Zhu (IHEP) – Synchrotron radiation absorption and vacuum issues in the IR, J. Seeman (SLAC)

Some highlights The CEPC IR optics have been improved – The strong bend magnets in the local chromaticity correction blocks have been softened and the L* has moved down to 1.5m The FCC-ee IR design is being studied – Double ring – 11 mrad crossing angle – A very flexible design to cover Z0 to ttbar Ecm range A crab waist IR design was presented that looked promising There was a very comprehensive talk on superKEKB background studies – Very extensive work on detector and local accelerator component modeling

Highlights (2) Two interesting studies of beam-beam limits – Scaling laws and simulations compared against measured values from several machines – Larger  y* gives more luminosity for CEPC design 2mm  y* should have more lumi than 1.2 mm  y* Presentation on pretzel design with bunch trains from CESR – Difficult to maintain even with extreme machine flexibility

Highlights (3) Three talks on L* choices – First talk also included general SR issues There is a lot of SR in the IR Beam tails are important – Second talk included general non-linear effects and suggested lowering beta maximum values – Third listed detector requirements and pointed out desire for a small radius IP beam pipe Comprehensive presentation on beam particle losses – Beamstrahlung is very important for the CEPC and FCC-ee

Highlights (4) Interesting presentation on a new detector using infrared SR to monitor beam conditions in real time Detector background simulations for CEPC – General indication is that backgrounds do not look too bad at this stage – More detailed simulations to follow A look at PEP-II B-factory issues for SR power and vacuum requirements in the IR – SR power must be carefully controlled – Everything in the vacuum system has to be water cooled

Summary Some general impressions and thoughts for further study – L* needs further optimization Final focus magnets are still quite strong Beta maximums are still fairly large Strong SR generators – Beam pipe sizes need further investigation – Beam-stay-clear definition – what is needed? Beam tail distributions

Summary (2) – Storage ring beams have beam halos The ILC does not. So ring backgrounds should be higher than the ILC? Beam backgrounds (SR and lost particles) will set IR beam pipe size(s) Beam tails used for PEP-II B-factory Minimal tail distribution since the B- factories do not have beamstrahlung

Conclusions We had a very interesting set of presentations and a great deal of discussion on many topics There is always much more to do and many good points were raised that will require further thought and study These large ring e+e- colliders (factories!) are very interesting machines with challenging issues!