Agenda and Summary:
1) Kicker for fast feedback -- Steve Smith
2) Discussion of e+ sources location and BDS, M.Woodley and all
3) Brief summary of ATF2 discussion from Nanobeam -- A.Seryi
4) Discussion of R&D list for 20, 14, 2, 0mrad options -- A.Seryi and all
Kicker for fast feedback
Steve presented design considerations for fast feedback kicker for 20mrad IR and
2mrad IR, assuming the kicker is located either inside of SD0 or just upstream.
The cupture range was assumed to be ~500nm for both x and y. Two plausible
solutions for kicker were investigated: unloaded stripline kicker and
ferrite-loaded single-turn kicker. The aperture requirements are different --
20mm in 20mrad and 180mm in 2mrad IR (see file "Snowmass
2mr design" for 2mrad tracking and aperture requirements). Correspondingly,
the kicker power is different as well-- 500W and 35kW (20mrad and 2mrad) for
stripline kicker and 75W and 4kW for ferrite-loaded kicker. All these cases look
technically doable, from the kicker design point of view.
Several issues were identified in discussion. First, the ferrite-loaded kicker cannot go inside SD0 or perhaps even near SDO, since it cannot be placed in high magnetic field. Second: if the stripline kicker placed inside of SD0, in order to obtain proper kicker impedance, there should be a gap between strips and SD0 aperture -- this will increase SD0 aperture by 25% or so, increasing pole tip field by ~50%. The SD0 magnetic design, especially in 2mrad case, may become too challenging. For these reasons, the kicker should be placed just upstream of SD0 in a drift space, as close as possible to SD0 (to minimize nonlinear effects, see notes on Oct 4, 2005).
Discussion of e+ sources location and BDS
Following the suggestion of wg3a, occurred at the end of Snowmass05, to locate
the e+ undulator source at the end of the linac and in front of beam delivery,
intensive discussion of consequences of such a decision have started. A document
has been prepared (see file "e+
source type") which argues with the end of the linac location and discusses
the consequences, in general and for BDS in particular, such as loss of BDS
upgrade flexibility and so on.
The wg3a suggestion may be based on assumption that there is a bend in the very beginning of BDS that may help separating gammas from undulator from the main electron beam. The file TDR & ILC BDS shows that there is no such bend in the present BDS baseline, and shows the differences of TESLA TDR BDS and ILC baseline BDS.
Accurate comparison of mid linac and end linac e+ source location show that there is no cost benefit to end of the linac location while many other factors favor the mid linac. In order to understand these cost differences, and list all the systems (mps, collimatiors, beam dumps, etc.) needed for either location, Mark generated sketch (see Mark's talk) of e+ source merged with rearranged BDS, to give min cost. Mark will also generate similar sketch for mid linac location, for cost comparison. One need to stress that the presented sketch does not represent a design, does not prove feasibility and is intended only for rough comparison of the cost and of the list of system with mid linac location.
Couple of additional issues were identified in discussion: a) depolarization of 250MeV positron beam (which has noticeable energy spread) during transport to the other side of IR may be a problem; b) as drawn on the sketch, the positrons go to the other side of IR under the IR hall, which does not seem to work as it causes severe problems for conventional facility group.
Brief summary of ATF2 discussion from Nanobeam
Brief summary of ATF2 discussion at Nanobeam 05 was presented by Andrei. Among
the things to consider are the following.
1) Need to make designs of bends.
2) Need to consider collimation in FF, to provide good background for IP size monitor.
3) Tests of tail folding octupoles can be performed at ATF2, with compact SC octupoles. Need to consider if optics need to be modified for such a test.
4) FD design need to be done.
For the latter, it was discussed that conventional EM FD would be baseline for ATF2, while SC compact FD may be considered for future upgrades.
For the FD design, the aperture need to be chosen. If we aim to 2.8microns/35nm in X/Y at IP, with beta* 4mm/0.1mm, then in the FD we have betaX=5000m (see file "ATF2 optics"). Then the X beam size in FD is about 3.1mm in FD (dispersive size for dp/p=0.001 is much smaller). The ten sigmas criterion gives radius r=30mm for the FD. This needs to be further discussed and then magnet and vacuum chamber design should proceed.
Discussion of R&D list for 20, 14, 2, 0mrad options
The list of R&D items specific to BDS configurations with 20,14,2,0mrad crossing angle is being prepared and was presented by Andrei. Couple of missing items were suggested by the group and were added. This list will be sent to whole community for discussion. The group also suggested that ranking of R&D items, perhaps similar as was done for TRC, may be appropriate and should be suggested.
Andrei Seryi, 11/02/05