1) Options for ATF2 diagnostics optics, emittance scaling in ILC chicanes --
2) 20mrad extraction line design update -- Yuri Nosochkov
3) ILC-FF9 Collimation system performance -- Sasha Drozhdin (presented by A.Seryi)
4) Update on QD0 and Extraction line quad design -- Brett Parker, et al.
Mark discussed the present ATF diagnostic section and discussed how the more ideal design would look like. Three options for improvement of ATF2 diagnostic section were presented. The additional space required ranges from 10m in the first version and 5m in the second version. The longer version have several drifts with about one meter length which can be used for experiments such as nano-BPM, while the shorter version have half-meter drifts, which would be already harder to use for such purpose. The third version is based on Paul Emma's suggestion to place several wire scanners in a drift, which give really straightforward emittance measurements. The required additional space is also about 10m in this case. This last version require further optimization of the optics.
Mark also presented tracking results of the emittance growth due to upstream polarimeter chicanes. The emittance growth is proportional to the dispersion in the fifth power, and is about 1% at 1TeV CM with 10mm dispersion. The present ILCFF9 design has 5mm dispersion, which seem to be too small because it makes the Compton electrons exit so close to the beam pipe. Increase of the dispersion to 10mm is acceptable from the emittance point of view and also for the separation of the Compton electrons. There is also a request to increase the distance between the central bends in the chicane to 8meters from the present 1.4m. Consequences for the optics due to this change will be studied.
Yuri presented an updated version of the 20mrad extraction line design, where he used the extraction line optics with the first quad defocusing DFDF (both DF... and FD... version were presented at LCWS05) and optimized it further. The disrupted beam losses in this extraction line are twice smaller than in the previous version for the beam without offset and somewhat larger for the beam with larger vertical offset (of about hundred nm). Losses at superconducting elements are rather small, about 1.8W.
Sasha investigated collimation performance of the latest ILC-FF9 design. There is significant improvement of the performance in comparison with the previous version, which is attributed to the improved bandwidth of the betatron collimation system and the system as a whole. There are also new findings in comparison with the studies performed during the Collimation Task Force. The bremsstrahlung photons produced in the spoilers, absorbers and masks are now taken into consideration and these photons were found to deposit from 0.2 to 1.2kW in several 0.2m long protection collimators. (For 1E-3 fraction of the beam in the halo). Implications of such losses and needed workarounds will be studied.
Brett presented an updated engineering design of the 20mrad IR quads package which is now combined with the antisolenoid. The final quad and the first extraction quad start at the same distance from the IP, to provide optimal performance of the extraction line. The antosolenoid location and the sub-structure (it consists of four coils that can be trimmed individually) are optimized to compensate the effects of the main detector solenoid on the beam size.
Andrei Seryi, 04/05/05