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Beam Background Simulation at Belle/KEKB

Beam Background Simulation at Belle/KEKB. O. Tajima (Tohoku university). Belle Collaboration. Motivation SR background Particle background Feedback to the detector design SR alarm Summary. Motivation.

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Beam Background Simulation at Belle/KEKB

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  1. Beam Background Simulation at Belle/KEKB O. Tajima (Tohoku university) Belle Collaboration • Motivation • SR background • Particle background • Feedback to the detector design • SR alarm • Summary

  2. Motivation Detector had serious radiation damage at the beginning of the experiment (SVD 1) • Beam BG simulation is essential to • Understand the reason of rad. damage • Feedback to the design of the detector  Control of the BG level & accelerator operation criteria

  3. Particle BG from HER and LER Beam-gas scattering in the entire ring (Bremsstrahlung and Coulomb) Touschek effect Beam-induced Backgrounds Synchrotron Radiation(SR) BGfrom HER Soft SR: radiated at HER upstream Ecrit ~ keV Hard SR: backscattering photon (BS-photon) Ecrit ~ 40 keV

  4. SR Background (1) SR wattage calculation based on orbit • HER contribution is only considered  SR intensity & spectrum from each magnets  Ecrit ~ keV Background simulation is performed by using EGS4 & Geant4  Exact geometry of beam-pipe is integrated  Photons traced down to 1 keV (0.25keV for G4)  Reliable EM interactions (L-edge X-rays of Au etc.)

  5. SR Background (2) SVD gain was droped for 10 days !

  6. SR Background (3) The reason is the SR from HER !! Estimated dose w/ actual orbit condition at 1st layer (kRad/10days)  Bad orbit condition cause it !!

  7. dose  φ- dependence  SR Background (4) HER φ- dependence is reproduced by the simulation !

  8. SR Background (5) Set the limit for kick angle of steering magnet ! Au coating is also effective !

  9. TURTLE: simulation in the ring • Tool for beam transport & beam-gas scatterings • The entire ring, up to one whole turn • Bremsstrahlung&Coulomb scattering GEANT : simulation in / around the detector • Full detector simulation based on Geant3 • 8.3 m HER / 6.5 m LER sides (up to QC2 magnets) • Magnetic fields of Quads and solenoids are included Particle Background (1) TURTLE + GEANT simulation on CO at 1 nTorr

  10. Particle Background (2) Belle 8.3 m 6.5 m IP

  11. Particle Background (3) Comparison with measurement based on Single-Beam run (Dec 2000) Dose on 1st layer (kRad/yr) The values in “(…) “ means no contribution from scatterings on materials outside the vacuum chamber Reproduce the measurements !

  12. SVD2 (1) 2cm 1.5cm

  13. SVD2 (2)

  14. Particle BG on SVD2 (1) (kRad/yr)

  15. Particle BG on SVD2 (2) SVD2* (r=1cm) better SVD1.4 (r=2cm) SVD2 (r=1.5cm)

  16. Soft SR BG on SVD2 (1) Based on the two orbits

  17. Soft SR BG on SVD2 (２) Dose during the Physics-run (kRad/yr) ex = 24nm, ey / ex = 3%, b*x / b*y = 63 / 0.7cm A few kRad/yr during physics runs

  18. Soft SR BG on SVD2 (3) Dose during the Injection (kRad/yr) Xoffset = 10mm, sx = 0.9mm A few kRad/yr during injections

  19. Hard SR on SVD2 (by Geant4 / EGS4) Cu B.S. -SR Hard-SR E deposit compton L-edge of Au K-edge K-edge of Cu Preliminary 20 ~ 30 kRad/yr (?)

  20. Expected Dose on SVD2 Particle BG  ~80 kRad/yr SR BG  20~30 kRad/yr Total ~100 kRad/yr Lower BG than till now (~2/3) Better VTX resolution is expected Higher tracking efficiency Stable data taking for a long time Will be checked by real operation from Oct

  21. SR alarm(1) Online alarm system based on the SR-sim. • Bad operation condition is rejected • Control the SR BG level • Challenging accelerator operation • Real orbit calculation from the beam position monitor, BPM (d=100mm) • Calculation of SR wattage distribution • 3. SR background estimation

  22. SR alarm(2) Real orbit is calculated by c2 fitting with IP constraint (<1mm)

  23. SR alarm(3) Performance System is almost ready ! To be installed soon !

  24. Understand reproduce the study / experience on SVD1 Feedback Detector / orbit was designed based on sim.  lower radiation damage ! (~100 kRad/yr)  can be checked soon for SVD 2 ! Summary Simulation of Beam BG (SR & Particle) Control Alarm system using real time SR sim based on actual orbit  start soon !

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