Agenda and Summary:
1) Fast feedback hardware discussion (location of kicker & BPMs, etc.) --
Phil Burrows, Tony Hartin, Linda Hendrickson, Steve Smith, Glen White, et al.
We start from reviewing Tony's talk at Snowmass
1a) Comments on kicker location -- A.Seryi
2) Status of 14mrad extraction optics -- Y.Nosochkov
3) Optimization of anti-DID for SiD, LDC, GLD -- A.Seryi
4) Incoming and extraction lines layouts -- B.Parker
Fast feedback hardware discussion :
The group discussed location of hardware for fast feedback (BPM and kicker),
starting with Tony presenting his Snowmass talk. In his detailed study, Tony
evaluated the effect of background (pairs, etc) on feedback BPMs, versus its
location or other parameters. For example, it was found that placing the BPM
after the first extraction quad in 20mrad case would not be acceptable. When the
BPM is placed behind the luminosity mask and before the QEX1, the number of hits
is acceptable, and is also decreasing as BPM moved closer to QEX1. For 2mrad
case, the location behind the luminosity mask is acceptable as well.
Discussing BPM location choice for the baseline, the following tentative decision was suggested:
a) 20mrad IR: BPM just behind the lumi mask;
b) 2mrad IR: BPM just behind the lumi mask;
c) 14mrad: BPM may be behind the lumi mask or it may be closer to QEX1 (in 14mrad L*extr=6m) where the number of hits is reduced. One need to evaluate if BPM can be installed in that place (which is inside of QD0 cryostat) and would not limit the aperture.
As for the kicker location, if we assume that the kicker should not go inside of QD0, so that it would not limit its aperture, the next best choice (in present FD) is just upstream of SD0 (see Andrei's comment). In this case the nonlinear effect due to orbit offset in the sextupole SD0 is minimized (the feedback range of 20sigmaX and 70sigmaY or more is possible). If the kicker is placed closer to QF1, the nonlinear effect is larger, and the range of feedback is reduced (to about 5sigmaX and 10sigmaY). Another possible location of the kicker is inside of SD0 -- this needs further studies. One other issue for the kicker in 2mrad case -- its aperture needs to be rather large, up to 9cm in radius or so.
Status of 14mrad extraction optics :
Yuri presented modifications of extraction optics for 14mrad case, where the L*extr is increased to 6m, to give room for incoming quads. Yuri also increased space allocated for crab-cavity to 4m and also considered two options for photon aperture based on photon angles 0.75mrad and 1.25mrad. The optics provide all the same functionality as previous 20mrad version, such as downstream energy spectrometry and polarimetry with R22=-0.5, and in terms of beam losses along the beamline it performs better than the previous version.
Optimization of anti-DID for SiD, LDC, GLD :
Andrei presented optimized anti-DID for SiD, LDC and GLD for the case of
intermediate crossing angle 14mrad. The use of anti-DID is possible with smaller
crossing angle since the synchrotron radiation (SR) effects are considerably
reduced, and the DID field can be optimized not for the incoming, but for the
The anti-DID field strength was optimized to maximize the number of pairs directed to extraction aperture. It was found that, due to anti-DID, more than 50% of pairs can be directed into extraction aperture, helping to improve background.
The anti-DID does increase the SR effects for the incoming beam, but the effect is negligible in SiD (luminosity drops by less than 0.2%), very small in GLD (less than 1%) and small in LDC (about 2%).
The modified DID field shape with flattened central region was used for GLD and LDC, as desirable for ease of TPC calibration (see notes on September 27, 2005).
The files with solenoid and anti-DID field data are posted, see links on the left.
Incoming and extraction lines layouts :
Brett presented layouts of magnets in incoming and outgoing beamlines, which serve as part of the input for detailed engineering design of IR magnets. The IR magnet design for 14mrad is ongoing and will be discussed on one of the next meetings.
Andrei Seryi, 10/04/05