News from the interaction region study Bernhard Holzer, Anton Bogomyagkov, Bastian Harer, Rogelio Tomas Garcia, Roman Martin, Luis Eduardo Medina Presented by M. Koratzinos FCC-ee (TLEP) Physics Workshop (TLEP9) 4 February 2015

This talk There has been some progress since the last meeting! I will show some fresh results The work still goes on I will transmit your feedback to the people that do the work M. Koratzinos2

The backdrop We pursue two different IP designs – One design is a small crossing angle no crab waist design (baseline) – CERN. Also this design does not have a local chromaticity correction. – this is done “a la LEP”. – The second is a more ambitious 30mrad crab waist design – BINP and CERN M. Koratzinos3

Small xsing angle approach Basically what was shown in Beijing during HF2014 Chromaticity correction “a la LEP” works Momentum acceptance is still not good enough New: SR power at the IR M. Koratzinos4

CERN IR design based on generic lattice for LINACs local chromaticity correction necessary due to high luminosity goals spacial separation of functions → modular s [m]  [km] D x [m] FFSCCSVCCSHMS  x  y D x CERN IR design for tt operation. R. Martin (CERN)

Geometry FCC-hh x [m] Beam 1 Beam s [m] x [m] FCC-ee, CERN design e+e-e+e- horizontal size of FCC-ee design ≈ 2 m → reasonable not yet included: matching section bending beams back together RF section FCC-ee interaction region currently much longer than FCC-hh R. Martin (CERN)

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FCC-ee sextupole scheme (a la LEP) SF1SF2SF1SD1SD2SD3 2 sextupole families in horizontal plane (90 degree lattice) 3 sextupole families in vertical plane (60 degree lattice) Separate sextupole families in each arc B. Harer

W functions for 1 quarter of the lattice IP Arc 1 Arc 2Arc 3 The ring here has 12 arcs and 4 equidistant interaction points This to be contrasted with a local chromaticity correction that appears to give much better results. A well-matched W function that shows the creation of chromaticity at the IR and the compensation of it in the neighbouring arcs B. Harer

Momentum acceptance The following plots show the change of the tune when the beam energy deviates from the ideal one. Blue line: no sextuples Green line: sextupoles on, equal strength Red line: sextuples on, matched Left plots: beta* of LEP 1.75m/0.07m Right plots: beta* of FCC-ee 1m/0.001m M. Koratzinos10

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Summary – small xsing angle Have tried the LEP approach where chromatricity is corrected in the arcs. Momentum acceptance is a factor of 10 worse than needed. But we can reproduce the LEP momentum acceptance more or less (~1% after optimization) Take home: we need the local chromaticity correction M. Koratzinos12

Second approach: crab waist This approach has become more complete at this stage There is a new and improved IR design that addresses some of the criticisms of the earlier design (SR at IP, second bend) The IR design has been married to the arc optics We finally have the first results regarding DA (Dynamic Aperture) M. Koratzinos13

Crab waist interaction region Work of Anton Bogomyagkov and colleagues from BINP Anton has studied two working points, both of which give good results. The changes since the last meeting are as follows: – The first dipoles are moved by about 20m further away from IP, made dipoles longer and weaker, – got rid of achromatic bend (which made the beam lines parallel prior entering the arc). These changes allowed to move fans of synchrotron radiation further away from IP, without increasing the length of the interaction region (new design is even a bit shorter) (also an extra sextupole is installed at the end of the final focus telescope (FFT) to control third order chromaticity without disturbing dynamic aperture much.) M. Koratzinos14

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Final focus layout Here the situation is complex as we are at a region where both the machine and the experiment claim territory. As a first iteration, and with agreement with Gigi Rolandi it was agreed that: – Area <100mrad is under the jurisdiction of the machine - but note that a luminometer can fit there! – Area >100mrad is under the control of the experiment – The possible range of values for the solenoidal magnetic field are: Strength: 2-4T Length: 7-13m M. Koratzinos16

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Dynamic aperture The tune plots shown are not the last word regarding momentum acceptance (but only a necessary condition) The CERN team has used the BINP IR design together with the CERN arc layout to produce the first DA plots M. Koratzinos31

Dynamic aperture It shows the minimum aperture of the entire x-y phase space after ~100 turns at 120GeV. Unoptimized Currently: ~7  between -0.9%-0.2% M. Koratzinos32 DA under the influence of the sextuples calculated for Anton’s old interaction region, which was matched to Bastian’s arc design. The DA is limited at nominal momentum to 7 sigma (low but sufficient at present) and breaks down for momentum deviations. Plot took 1 week of intensive CPU work. Not sufficient, but this shows that we do have the tools to progress Luis Eduardo Medina, Rogelio TOMAS GARCIA

Conclusions The problems are not easy! Good progress has been made since the last meeting We do have the tools to make progress First Dynamic Aperture plots are encouraging but not yet sufficient M. Koratzinos33

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