M. Sullivan Apr 27, 2017 MDI meeting Update of the SR M. Sullivan Apr 27, 2017 MDI meeting

Outline Current beam pipe layout Improved SR calculations How Lumi-monitor fits in Improved SR calculations Binning for critical energy histograms was found to be too coarse. This has been resolved. New tt SR background estimate HH running SR background estimate WW running SR background estimate Summary

Here is where the beam pipe needs to be enlarged LumiCal HOM absorbers

Features The natural chamber wall geometry is OK All LumiCal tracks now have a 20 mrad or higher angle of incidence to the beam pipe walls There looks to be enough room on the other side of the beam pipe for a NEG vacuum pump Now we come to the next question…..

Shielding The question now arises about shielding the central detector from SR from the last bend magnet The LumiCal needs a window in the beam pipe where we can no longer put shielding For the Z running this is probably not an issue The photon energies are very low (Ave scattered=1.8 keV) But for the Top running this is more important Ave scattered is 200 keV Effectively the central part of the beam pipe increases from +/-12.5 cm to +/-50 cm due to the LumiCal window This will increase the number of photons going into the central chamber (factor of 10? More?) GEANT simulation comparison will tell us the answer

tt scattered photon energy spectrum in Jan. The photons that cause trouble are coming from the high energy tail of the bend radiation

Scattered energy spectrum for tt in Mar. 522458 out of 100 million incident scatter through the tip I found an inaccuracy in my code where the binning for the critical energy histograms was calculated too coarsely. Came about because there are very strong FF quads and a very soft last bend magnet

Energy scattered/incident ratio

Scattered energy spectrum from HH 433219 out of 1billion incident scatter through the tip Number incident > 10 keV is 187 million/xing so 81,000 scatter from the tip

Scattered energy spectrum for WW 389692 out of 10 billion incident scatter through the tip Number incident > 10 keV is 28 million/xing so 109 scatter from the tip

WW scat. ener. with expanded scale

For the Top running 2.1109 photons are incident on the mask tip from every beam bunch (9.9108 > 10 keV) 0.52% scatter through the mask tip (5.15 million) Of these, 1.4% go through 1 cm of Ta (72,000) Or 0.16% go through 2 cm of Ta (8200) This is looking like it might be OK We will probably need 2 cm of shielding (Ta, W or Pb) near the mask tip Once the photons are going through the shield at a 45 deg or smaller angle of incidence 1 cm of shielding should be enough A detailed GEANT simulation should verify this

What about the other running points? SR photon critical energies are listed here The critical energy of the last soft bend magnet For the Top (175 GeV) – 100 keV For the Higgs (125 GeV) – 40 keV For the WW (80 GeV) – 9.5 keV For the Z (46 GeV) – 1.8 keV (3.6 keV?) More simulation runs with the GEANT4 model of the beam pipe Do we want/need the LumiCal for the Higgs? Stay tuned……

Summary The LumiCal looks OK at the Z running Even with smaller beta* optics (needs to be checked) We need a Be beam pipe for the LumiCal window in order to minimize the RL to the LumiCal and to minimize the HOM power in this region The LumiCal window will cause central detector SR backgrounds to increase at the Top running because of the higher energy of the scattered photons and some reduced shielding but in general SR backgrounds look like they can be controlled

FF quads Magnet designs are converging and the next big step is to get initial dimensions for the cryostats Can we have warm bores as asked? How much actual space is needed for the magnets and correction coils and compensation coils

Conclusions A great deal of progress has been made in deciding on baseline parameters and general layout of the IR SR at the Z does not appear to be an issue due to the very low photon energies SR backgrounds at the Higgs and Top will be more of an issue. The photon energies are significantly higher, but at first blush it looks like they can be controlled