Minutes of 107th FFIR/BDSIM and 29th ILC-Asia WG4 meeting on 6/1/2005

ILC Asia WG4 : Minutes of 29th meeting
June 1 10:00
Rm.425 bldg.3 at KEK.

(1) Series of meetings and mini-workshops

There were a series of meeting/workshop as follows;

(2) Shintake monitor

T.Suehara reported measurements of beam halo at the ATF extraction line. The halo was measured in the horizontal direction for 5 -10 &sigmax by the wire scanner increasing gains of the detector; i.e. photomultiplier for the air cherenkov counter. The gain was calibrated at the peak in the wire-scanned signals. The halo is not Gaussian shape but power one of &sigma-4. The halo intensity was estimated to be about 1% for x > 5 &sigma. The S/N was about 2 at x=10&sigma. He expressed necessity of beam-collimation at upstream of the extraction line in order to reduce background a the Shintake monitor. At present, the minimum aperture is located at the septum (BS1X - 3X), where the vertical and horizontal full apertures are 7 and 14mm, respectively. The beam sizes are listed in a file of http://acfahep.kek.jp/subg/ir/bds/atf2/ff3.5_disp_b.txt .

Also, he measured background at 6 points around the beam dump by a Cs-I crystal detector with a photomultiplier as shown in his slides. Observed signals has two components with fast (prompt) and slow timings, where the slow one is delayed with several hundreds nano seconds after the fast one. The fast signal becomes larger near the dump, while the timing becomes slower. So, the fast one might consist of backgrounds both from the upstream and the dump. The slow signal was observed to be more delayed far from the dump. He could reproduce the timing structure of observed signals by GEANT4-simulations of back-scattering background from the dump, where the slow component was identified as neutrons.

Next background study will be planned in next week of 6/6-10. The goals are (1) timing decompose of the fast signal to separate the upstream and backscattered background, (2) to search for "optimal" location of the detector with least background, and (3) measurement of beam halo in vertical direction.

Air cherenkov counter might be more suited for the Shintake monitor for faster timing response as well as less affected by charged background than the crystal detector. So, it was pointed out that the background should be studied with the cherenkov counter too.

(3) Other issues

We discussed on necessary area for an optional laser facility at the ATF2 for available space in the assembly hall, KEK. The facility has been investigated by T.Takahashi, J.Gronberg and V.Telnov etc. . The area can be about 10x10m2, while the length of laser cavity must be 100m for 300nsec bunch spacing at the ILC photon collider. They will update the Appendix of "Proposal of laser facility" in the ATF2 proposal.

Estimation of tolerances is emphasized at the ATF extraction line in addition to those at ATF2-FF line, since some of present magnets and power supplies might be upgraded. Also the tolerances should be compared with those at the ILC-BDS.