1. Synchrotron Radiation (SR) in Super-KEKB / Belle Osamu Tajima ( Tohoku univ )

2. Contents Introduction (Soft/Hard-SR, simulation tools) Experience at Belle - Troubles in 1999 - Efforts for SR reduction - Current Status Ideas for SR reduction in Super-B Dose is given only for 1 st layer of SVD

3. Synchrotron Radiation (SR) Scattered at downstream photon-stop (OC2RE chamber) Soft-SR High energy SR is generated in OCS magnet Hard-SR (backscattering) Several keV keV ~ 150 keV Belle

4. Beam orbit in Soft-SR simulation We can estimate real orbit from BPM Real orbit is calculated by  2 fitting with IP constraint (<1mm) Design orbit is adopted for Super-KEKB

5. Simulation Tools in Detector etc. Simulate down to 1 keV or less Photoelectric-effect is important in keV range ex. Au L-edges (14keV…), Cu K-edge (8keV) etc. Requirements EGS4 / Geant4

6. #### Experience at Belle ####

7. Belle had miserable experience Understanding & Reduction are Important ! Soft-SR killed readout chip Current limited, 100mA by high rate Hard-SR

8. Simulation reproduce Gain-drop azimuthal distribution actual orbit by T.Abe (KEK)  Solved by limiting steering magnets operation  No more troubles

9. Reduction of Hard-SR Put photon-stop far place : 6  9.5 m ~ 0.4 Chamber material : Al  Cu ~ 1/3 Energy spectra of Hard-SR (simulation) ~1/10 Higher current 100  1100mA achieved !!

10. More Reduction Efforts Au-coating ! crescent shape SR-mask SVD 2.0

11. More Reduction Efforts Au-coating ! crescent shape SR-mask Au coating absorbs low energy photon less than 8 keV SVD 2.0

12. More Reduction Efforts Au-coating ! crescent shape SR-mask Saw-tooth surface shape in Ta blind Soft-SR reflected on Ta SVD 2.0

13. More Reduction Efforts Au-coating ! crescent shape SR-mask Crescent shape SR-mask blind Be section from Soft-SR SVD 2.0

14. More Reduction Efforts Au-coating ! crescent shape SR-mask SVD 2.0 Hard-SR is shielded by Ta-chamber

15. Dose expectation SVD2 (r=1.5cm) Scattered at downstream photon-stop (OC2RE chamber) Soft-SR High energy SR is generated in OCS magnet Hard-SR (backscattering) Several keV keV ~ 150 keV few kRad/yr 29 kRad/yr

16. Azimuthal Distribution of SR 33 kRad/yr at HER 1.1A 21 kRad/yr at HER 1.1A Single-Bunch 15 mA (trigger-timing is adjusted) Total 0.8 A w/ 1284 bunch (random timing) Only above threshold 10 keV Simulation complements below thereshold simulation 29 kRad/yr Hard-SR simulation

17. Current Status of SR at Belle Simulation reproduced experience Current beampipe (r =1.5 cm) at Belle is designed based on BG simulations Hard-SR is dominated (~30 kRad/yr) Data is consistent with simulation Success of beampipe design r bp =1.5cm Strong support for - Design Concept in Super-B - Reliability of BG Simulation

18. #### Study for Super-B ####

19. Super-KEKB Machine Parameters KEKBSuperKEKB Horizontal emittance24 nm33 nm x-y coupling~ 3 %6.4 %  x * /  y * (cm) 63 / 0.730 / 0.3 Beam current1.1 A4.1 A Crossing angle22 mrad30 mrad HER-beampipe tilt11 mrad15 mrad

20. HER  Functions Based on IR_HER6.sad

21. Beampipe in Super-Belle  Can we also scale SR-mask height ? Scaled to 2/3 ( r bp 1.5  1.0 cm)

22. Discussion for SR-mask (r bp =1cm) 200 kRad/yr 2/3 scale 2 MRad/yr !!

23. Discussion for SR-mask (r bp =1cm) Mask height should be same as r bp =1.5 cm case ( ~2.5 mm height) 200 kRad/yr 2/3 scale 2 MRad/yr !! Acceptable height

24. Discussion for SR-mask (r bp =1cm) outside inside 200 kRad/yr

25. Discussion for SR-mask (r bp =1cm) outside inside outside inside If vertical direction is higher ? 200 kRad/yr

26. Discussion for SR-mask (r bp =1cm) outside inside outside inside 80 kRad/yr 200 kRad/yr

27. Dose distribution Sym. SR-mask ~20 kRad/yr ~50 kRad/yr QC1L(-3m) during injection QC2L(-7m) at stored ~10 kRad/yr

28. Dose distribution Sym. SR-mask ~50 kRad/yr QC1L(-3m) at injection QC2L(-7m) at stored ~10 kRad/yr !! WARNING !! Soft-SR is localized ~20 kRad/yr

29. SR Alarm Online Alarm system based on the SR-sim. 1. Real orbit fitting with BPM (  =100mm) 2. SR simulation into detector  Monitor Soft-SR immediately  Control BG level (hopefully)  Permit challenging accelerator operation BPM Operator simulation Orbit fit Alarm Feed-back

30. Hard-SR at Super-KEKB / Belle - No correlation with beampipe radius - Determined by beam current and solid angle HER current: 1.1 A  4.1 A beampipe tilte: 11 mrad  15 mrad  29 kRad/yr(SVD2) x (4.1/1.1) x (15/11) ~ 150 kRad/yr In case of current configuration For Hard-SR reduction  Reduce scattering on photon-stop  Put photon-stop far place

31. Hard-SR : materials of photon-stop Cu:150 kRad/yrAg:100 kRad/yrTa:140 kRad/yr Heavy material reduce compton scattering K-edge of heavier material is higher  Ag looks good for Radiation Dose  Wattage w/ Ag (Ta) is 36 (64) % higher than Cu

32. Idea for Hard-SR reduction HER-beam If we can bend beam  photon-stop far place SR If 2 times far place  1/4 BG

33. Summary We had serious troubles by SR, but Solved  simulation reproduces them Beampipe for SVD 2.0 (r bp = 1.5 cm) was designed based on the BG simulation  Measured dose agrees to expectation Basic design for Super-B is same as SVD 2.0, r bp = 1.0 cm scaled to 2/3 SR-mask shape is symmetric w/o 2/3 scale No serious increase for Hard-SR  Soft / Hard-SR ~ 80 / 150 kRad/yr  only 8 times higher than current SR-BG No problem for Super-KEKB / Belle !

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35. QUAD Parameters s (m)k1 SuperKEKBKEKBSuperKEKBKEKB QCSR (+2m)+ 0.72 ~ 1.68+ 1.48 ~ 2.40- 0.46- 0.30 QCSL (-1m)- 1.52 ~ -0.52- 2.08 ~ 1.12- 0.56- 0.38 QC1L (-3m)- 3.12 ~ 2.48- 3.61 ~ 2.99- 0.37- 0.32 QC2L (-7m)- 7.70 ~ 5.70- 8.23 ~ 6.17+ 0.25+ 0.24 Based on IR_HER6.sad

36. SR Background (1) X offset = 10mm,  x = 0.9mm  x = 24nm,  y /  x = 3%  * x /  * y = 63 / 0.7cm ~ 1 kRad/yr in physics runs ~ 1 kRad/yr in injections Soft SR : radiated at HER upstream E crit ~ keV Orbits : Nov 7(2001), May 15(2002) SVD1.5 ~ 0.5 KRad/yr