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Lifetime of HPK Square-shape MCP-PMT

Lifetime of HPK Square-shape MCP-PMT. T. Mori ( Nagoya University) On behalf of Belle II PID group Dec. 1, 2010 Fast Timing Workshop Cracow , Poland. Belle & Belle-II Experiments. Super B-factory. Belle detector. Belle II experiment. K /π-ID is important Belle: 3σ. K /π-ID power: 4σ

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Lifetime of HPK Square-shape MCP-PMT

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  1. Lifetime of HPK Square-shape MCP-PMT T. Mori (Nagoya University) On behalf of Belle II PID group Dec. 1, 2010 Fast Timing Workshop Cracow, Poland

  2. Belle & Belle-II Experiments Super B-factory Belle detector Belle II experiment • K/π-ID is important • Belle: 3σ • K/π-ID power: 4σ • ex. S/N ×5 for B  ππ • High background rate 3.5GeV BelleIIdetector cross section 8GeV 1.5T Install here(10cm gap of barrel part) 1.2m 2.6m e+: 4GeV e- : 7GeV Higher statistics： Higher luminosity (×~40) B-factory ＆ Higher accuracy ： Belledetector upgrade TOF + ACC (ACC: Threshold type Aerogel Cherenkov Counter) TOP counter (Time Of Propagation) For barrel part Backward Forward Fast Timing WS, Cracow

  3. TOP Counter • Time Of Propagation counter • RICH + TOF technique • Cherenkov radiator + time sensitive screen • Position (x, y) (RICH) ⇒ Position + time (x, t) • Very compact & simple • Radiation hardness π K ～ O(1m) K, πwith p = 4GeV/c ⊿TOP = 40ps (L ~ 1m, ⊿θC = 6mrad) ⊿TOF = 30ps (L ~ 1m) ⊿t ~ O(100ps) Fast Timing WS, Cracow

  4. Performance & Important Device Separation power : • Performance definition • σphotodetector : TTS of photodetector • Ndet: number of detected photons • Requirements • TTS : <50ps • Gain : 1.0×106 • Single photon detection • Enough statistics for TTS • QE : >20%@λ=400nm • Available in B -field > ~ 50ps (Chromatic) Photo-detector is very important Our selection: MCP-PMT Fast Timing WS, Cracow

  5. ~400m Square-shaped MCP-PMT: SL10 Ordinary cylindrical MCP-PMT Typical signal shape Square MCP-PMT Channel φ ~ 10μm 27.5mm MCP(Micro channel plate) 27.5mm Co-development with Hamamatsu Photonics K.K. φ11mm ~4mm Single photon irradiation Fast Timing WS, Cracow

  6. Performances of SL10 Pedestal Single photon irradiation QE [%] Multi-alkali PC G ~ 106 • All requirements satisfied • Remaining factor: stability(Lifetime)in high photon rate • ~7x1012 photons/cm2/year • ~0.17 C/cm2/year • Estimated with TOF trigger hit rate • Cylindrical type: enough lifetime Number of events Number of events ADC [0.25pC] TDC [25ps] Wavelength [nm] σtts = 40 [ps] Fast Timing WS, Cracow

  7. Lifetime measurement for SL10 • Parameters • TTS • σphotodetector • Gain • Single photon detection • Enough statistics for TTS • QE • Ndet For single photon test calibration PMT Load of photons & single photon test done in same setup ~40-photon/pulse 1k – 40kHz Fast Timing WS, Cracow

  8. Result: TTS, Gain • Decrease • Good Stability • TTS is stable • Single photon detection is OK 0 0.4 No problem Time in Belle II experiment [years] Fast Timing WS, Cracow

  9. Result: QE • QE difference • SL10 • Cylindrical • Lifetime • QE degradation: predominant factor • Gain: linearly decrease; still OK for single photon detection & TTS • TTS: Stability confirmed Cylindrical Why? Previous SL10 Let’s see QE in detail Fast Timing WS, Cracow

  10. QE Variation: Wavelength Three step model: Fitting: ratio of QE • Increase of work function dominates T : transmittance A: mechanical factor (effective region) φ: work function ⊿φ: variation of work function YJ0011 A(t)/A(t=0) 0.98±0.04 ⊿φ0.27±0.07eV φ 1.56±0.13eV QE [%] Beforeaging After aging Work function Wave length [nm] Fast Timing WS, Cracow

  11. QE Variation: Position QE after aging QE before aging • Surrounding part: large QE drop • Ion feedback? • Structure? y y [mm] y [mm] 16 x [mm] 1 x [mm] x Fast Timing WS, Cracow

  12. Effect of Ion Feedback? Positive Ion damages same position as signal photon irradiation Lifetime test with mask • Ion feedback • Mask: no effect • Ion feedback Lifetime test with mask Mask Window MCP-PMT QE variation without mask QE variation with mask Fast Timing WS, Cracow

  13. Inner Structure & Possible Cause Window Window PC PC Inner structure of Cylindrical type & square-shaped MCP-PMTs 1st MCP 1st MCP • Only NEUTRAL gas can pass through gap (∵electric field) 2nd MCP 2nd MCP Anode Anode E Ceramic tube Neutral gas Al-film Al-film Cylindrical: separated Square: connected Stainless tube Poisoning of multi-alkali PC with different gasses (INFN Milano – LASA, Via F.lli Cervi 201, 20090) We also found report saying CO2 and H2O affect QE: (Japanese Journal of Applied Physics 29, No. 10, p. 2087 (1990)) • Too much oxidation of Cs • variation of band gap • increase of work function Fast Timing WS, Cracow

  14. Modification of Inner Structure Window PC 1st MCP Ceramic insulator • Separate space to PC-side & anode-side • It is not high airtight • MCPs are changed with that of low outgassing type • To reduce amount of out gas Ceramic insulator 2nd MCP Anode Al-film Fast Timing WS, Cracow

  15. Lifetime for New SL10 • 2.5 [C/cm2] for relative QE 80% • 1.2×1014[photons/cm2] Before modification After modification Relative QE Output charge [C/cm2]  SL10 is available 0 10 1 DOI:10.1016/j.nima.2010.10.145 Time in Belle II experiment [year] Fast Timing WS, Cracow

  16. Summary • We are developing TOP counter for Belle-II experiment • TOF + RICH technique  TTS & Nphotons are important • Square shape MCP-PMT (SL10) is developed for TOP • Satisfies required performances (TTS, gain) for TOP • Lifetime of QE in high photon rate • We find possible cause of QE drop: Neutral gas (CO2 & H2O)  Improvementof inner structure against gas damage • Separate space to PC-side & anode-side by ceramic insulator • Low outgassingMCP 2.5C/cm2for relative QE 80% achieved • > 10 years under ~7×1012 photons/year/cm2 Fast Timing WS, Cracow

  17. Backup Fast Timing WS, Cracow

  18. Photon Hit Rate Estimation Main source: spent electrons  EM shower  Cherenkov light TOF hit rate in Belle experiment: 187kHz @ L=1034cm-2s-1 Belle spent electron simulator: 400 – 500 kHz @ L=1034cm-2s-1 Use 500 kHz electron  Geant simulation • TOP counter is implemented • Quartz radiator: 2650×454×20[mm3] • Without expansion volume • QE: 20% @ λ=400nm • CE: 60% • To be conservative Photon hit rate of MCP-PMT: 300kHz/(TOP module) Factor 20 is expected for Belle-II experiment with L~1036cm-2s-1 ☆ Photon hit rate (20×300 / (45.4×2))×365/2×24×60×60 / (QE×CE)= 6.9×1012 [photons/cm2/year] • effective factor ☆ Typical output charge (20×300 / (45.4×2))×365/2×24×60×60×G×e = 167 [mC/cm2/year] • Gain: 106 Fast Timing WS, Cracow

  19. Performance of TOP Counter • Performance definition • σtop= √(σMCP-PMT2 + σchromatic2 + σothers2) • Ndet: number of detected photons Separation power : y θ z x Photo-detector is very important Ndet 0.8Ndet  S  0.9S Fast Timing WS, Cracow

  20. Suppression of Chromatic Dispersion 350nm • Wavelength cut Suppression of chromatic dispersion with 350nm wavelength cut filter Group velocity of light σchromatic 50 25ps Number of Cherenkov photons Path length in quartz: 1m Transmittance of wavelength cut filter wavelength cut ⇒ TTS improve ⇒ fine tune Ndet decrease Fast Timing WS, Cracow

  21. Number of detected photons Fast Timing WS, Cracow

  22. Channel ~10m ~400m Photo-detector Square type MCP-PMT • Requirements • Gain : 1.0×106 • TTS : <40ps • QE : >20%@λ=400nm • Available in B -field Co-development with Hamamatsu Photonics Only photo-detector satisfies requirements MCP-PMT (Micro Channel Plate) Channel φ~10μm, Bias angle of MCP : 13° Available in B-field Fast Timing WS, Cracow

  23. SL10 Fast Timing WS, Cracow

  24. Cylindrical & SL10 Fast Timing WS, Cracow

  25. Lifetime measurement for SL10 • Lifetime difference • Cylindrical • Square • Lifetime • QE degradation • predominant factor • Gain & TTS • stability confirmed For single photon test Cylindrical ~40-photon/pulse 1k – 40kHz Square Why? Fast Timing WS, Cracow

  26. Gain decrease • ADC plots Output charge After photon load Before photon load Fast Timing WS, Cracow

  27. E - λ Fast Timing WS, Cracow

  28. How the QE Degradation Occur? After measurement Before measurement QE fall Before • QE fall is not uniform • Ion feedback is not reasonable y [mm] y [mm] After QE [%] (y = 10[mm]) x [mm] x [mm] QE [%] x [mm] Before After Increase of work function Wave length [nm] Fast Timing WS, Cracow

  29. How the QE Degradation Occur? Initial QE QE fall Terminal QE Initial • QE fall is not uniform • It is not reasonable if it caused by Ion feedback y [mm] y [mm] Terminal QE [%] (y = 10[mm]) x [mm] x [mm] x [mm] Inner structure of CT0790 & square-shaped MCP-PMTs Possibility of neutral gas Fast Timing WS, Cracow

  30. Neutral gas assumption Tube Fast Timing WS, Cracow

  31. Lifetime of SBA-PC MA SBA1 SBA2 0 1 10 Use in Belle II [years] Fast Timing WS, Cracow

  32. Set up for Beam Test Quartz + MCP-PMT Fuji test beam line at KEK TOP Counter MWPC2 y y electron beam （2GeV/c） Trigger Counter Timing Counter x x MWPC1 Beam trajectory Vetocounter MCP-PMT t0 determination Subtract EM-shower events Fast Timing WS, Cracow

  33. Prototype test for TOP 1st 3rd 3rd 1st 2nd 2nd • Consistency confirmed data simulation N [photons] ch29 quartz transit time[25ps] transit time[25ps] Electron beam irradiation 915mm 3rd 2nd 875mm 1st Fast Timing WS, Cracow

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