=== Minutes of 1999/10/28 SVD meeting === Attendance: Asano, Casey, Hara, Hazumi, Heenan, Kaneko, Kawasaki, Moorhead, Mori, Okuno, Olsen, Tajima, Takasaki, Varner, Watanabe, Yamada, Yokoyama, Zontar (US people could not attend the meeting due to a trouble between NTT and DCS). 1. BG study results (Tajima) Tajima showed results of single bunch beam BG study. Cluster energy spectrum was compared between July (after steering magnet strength was limited) and Oct data. Hard (~30keV) X-ray is reduced by a factor of 20. Soft (<10keV) X-ray is reduced by a factor more than 100 and undetectable any longer. Dose rate was also calculated from the energy spectrum. The July data before the steering magnet strength was fixed, the dose rate due to soft and hard X-ray was calculated to be 2.7 Rad/s and 74m Rad/s. These rate corresponds to 97 kRad and 2.7 kRad for 10 A*hours. This is consistent with the damage observed by VA1s and DSSDs. Currently, the integrated doses for 10 A*hours are 0 Rad, 20 Rad and 50 Rad for soft and hard X-ray, and MIP, respectively for the current of 10mA. For the MIP contribution, you need to make corrections depending the beam current due to parabolic behavior of the particle BG. If we assume average beam current of 100mA, 5 kRad of dose is expected for 10 A*hours. 2. KEKB radiation interlock (Tajima) Currently, Injection will be inhibited at 40 mRad/s. Although this limits the HER injection rate, it does not reduce the total radiation due to the injection because the injection time simply gets longer. To avoid repeated bad injections, the new radiation interlock scheme was proposed and approved. * During injection, the injection inhibit is issued above 80 mRad/s. The beam boart is issued above 100 mRad/s. * During storage, the beam abort is issued above 30 mRad/sec with duration of more than 200s or above 100 mRad/s. * Hourly limit of 20~30 Rad/h is imposed. Injections are inhibited once this limit is exceeded. The time interval may be 2, 4 or 8 hours. We will test what is the best for the KEKB and the BELLE. * New scheme will tested for a week before it takes effect. 3. TOF trigger (Casey) Brendan reported the status of tsim-tof. He first remidned us that the current L0 rate can be described as 12*I+0.27*I^2 and it reaches as high as 70 kHz at 500 mA. This is above our limit of 40 kHz, which corresponds to 1% dead time. Please note that the situation will get better as the vacuum is improved. Then he studied efficiencies of various TOF trigger configurations as shown below. Cut BB(MC) Cont.(MC) HadronC m>0 99.9% 97% 100% mhits>1 99% 93% 98% mhits>2 96% 85% 94% dphi>45deg 98% 90% 98% The mhits>2 cut appears too tight. dphi>45deg cut can be useful if the rate is very high. He is working to understand the BG rejection capability of the each cut using real data. If you have a good idea on the TOF trigger, you can ask him to study it. 4. S6936-MOD results (Yokoyama) Yokoyama studied the shaping time dependence of the noise with S6936-MOD. Between 1us and 2us, the noise is relatively flat. The Vfp was also used to adjust the shaping time which complicate the noise calculation. He will measure the shaping time dependence again without changing Vfp and compare with the calculation. 5. SVD/VTX software status (Hazumi) SVD matching efficiency is measured to be 95% with hadronic events by Sumisawa without alignment. The Bhabha events has lower efficiency by 2-3% for unknown reasons. The peak of the cluster energy is about 19,000e for both sides. So, the SVD seems working fine. The alignment group obtained the first alignment constants using 60K cosmic data. The quality of the constants appears close to what we obtained with the SVD1.0. There is mean shifts in misdistance of Bhabha tracks and the direction is different between vertical and horizontal tracks. The CDC tracks also had similar shifts. (It turned out that the shift disappeared with correct script). 6. Monitor (Tsuboyama) Tsuboyama discuss the possibility that the FET and PIN is sensitive different radiation source. He compared PIN and FET integrated dose and its relation with LER and HER currents. It appeared PIN and FET responds differently to the HER and LER current. However, the sample of PIN and FET are taken at the different position (FW and BW). So, the difference could be attributed to the position dependence. He will study further. He also studied the flange temperature rise with the reduced cooling. -- Hiroyasu Tajima Department of Physics, University of Tokyo 7-3-1 Hongo, Bukyo-ku, 113-0033 Tokyo Email: tajima@phys.s.u-tokyo.ac.jp Tel: +81-3-5841-7593 (office) Tel: +81-3-5805-8093 (ISDN) Tel: +81-298-64-5200 x4917 (PHS@KEK) Fax: +81-3-5841-8058