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Synchrotron Radiation (SR) in Super-KEKB / Belle

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

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Synchrotron Radiation (SR) in Super-KEKB / Belle

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  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 1st layer of SVD

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

  4. Beam orbit in Soft-SR simulation • We can estimate real orbit from BPM • Real orbit is calculated by c2 fitting • with IP constraint (<1mm) • Design orbit is adopted for Super-KEKB

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

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

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

  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 ~1/10 Energy spectra of Hard-SR (simulation) Higher current 100  1100mA achieved !!

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

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

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

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

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

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

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

  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 rbp=1.5cm Strong support for - Design Concept in Super-B - Reliability of BG Simulation

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

  19. Super-KEKB Machine Parameters

  20. HER b Functions Based on IR_HER6.sad

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

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

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

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

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

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

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

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

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

  30. Hard-SR at Super-KEKB / Belle In case of current configuration - 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 For Hard-SR reduction  Reduce scattering on photon-stop  Put photon-stop far place

  31. Hard-SR : materials of photon-stop • 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 Cu:150 kRad/yr Ag:100 kRad/yr Ta:140 kRad/yr

  32. HER-beam HER-beam Idea for Hard-SR reduction SR 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 (rbp= 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, rbp= 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 !

  34. ##### backup #####

  35. QUAD Parameters Based on IR_HER6.sad

  36. SR Background (1) Soft SR: radiated at HER upstream Ecrit ~ keV ~ 1 kRad/yr in physics runs ~ 1 kRad/yr in injections SVD1.5 ~ 0.5 KRad/yr Orbits : Nov 7(2001), May 15(2002) ex = 24nm, ey / ex = 3% b*x / b*y = 63 / 0.7cm Xoffset = 10mm, sx = 0.9mm

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