ILC Asia WG4 : Minutes of 52nd meeting http://lcdev.kek.jp/ILC-AsiaWG/WG4notes/ January 26 10:45- noon Rm.325 bldg.3 at KEK.
We understand the issue which SLAC people worry, very well. We think that the issue must be resolved by a support of the copper pipe. The pipe should be rigidly supported at both edges of the Q-magnet. If necessary, the pipe can be surrounded by a Aluminum case or an additional support can be installed in the Q magnet since there is 2mm gap between the pipe and the magnet bore. ( the diameters of the pipe and the bore are 28mm and 32mm, respectively. )
In our conclusion, we do not need to change the material of the pipe for present production of 11 QBPMs at least. The material has been decided by detailed discussions with the magnet experts who have a lot of experiences at KEK-B factory. Honda-san will design the support of the pipe by the ATF2 project meeting, 2/3-5, SLAC. We would like to reach the agreement with the SLAC people at the meeting. We may need to define an installation procedure of the QBPMs with "soft" copper pipe into the Q-magnets. We will ask the PAL group for suggestions on the support design and installation method.
Kuroda has been investigating 6-pole component in the Q-magnets whose origin must be the fabrication and assembling errors. Results of two simulations were presented.
First, relative quantities of 6-pole component were assumed to be 0.001 (fixed) and variable for the 20cm long Q-magnets and the final doublet (QD0 and QF1), respectively, where the quantities are defined at radius of 10mm inside the magnets. The signs of these quantities were set to be positive, negative and random for all the magnets. So, the vertical beam sizes were calculated as a function of the final doublet 6-pole component with the three sign-cases. Necessary 6-pole component in the final doublet must be less than 5 x 10-4.
Next, tolerances of skew 6-pole components were studied with correction of roll and strength of the sextupole magnets near the final doublet, where the correction steps were assumed to be 1mrad and 1%, respectively. The skew components are uniformly distributed in azimuthal angle around the beam line, i.e. 2 &pi. When the 6-pole component quantity of the final doublet is 1 x 10-4, the vertical beam size became to 44nm at "95%CL" with the correction. Multiple corrections did not improve the beam size. Also, when the 6-pole component quantity of all the magnets is 5 x 10-4, the corrected beam size was 225nm at "95%CL". So, the skew effect of the final doublet is significant, and the tolerance should be much less than 1 x 10-4 . In discussions, there are questions on the step sizes of the correction; e.g. the FFTB mover has the roll resolution of 1μrad.
Also, he showed modifications of the ATF extraction beam line (EXT) for ATF2. In discussions, it was pointed out that the modifications depend on availability of 140A power supplies. Terunuma will finalize the modifications with taking account of the power supply availabilities.
At the next meeting, we will focus on the priority of issues at the ATF2 project meeting.