1. Candidate light sensors for CTA High precision measurements of ultra-low light level detectors for CTA project: PMTs and SiPMs Matthias Kurz Max-Planck-Institute for Physics Candidate lightsensors for CTA Matthias Kurz Max-Planck-Institut for Physics in Munich

2. Cherenkov Telescope Array (CTA) Initiated by MAGIC and H.E.S.S. European initiative to build the next generation large ground – based gamma ray instrument of ~ 10 times higher sensitivity ~700 scientists from 100 institutions (mainly EU, but also USA and Japan) Study of distant AGNs, Black Holes, Gamma Ray Bursts, as well as the galactic sources (Pulsars, Supernovae, mquasar,…) from 10 GeV to 100 TeV Answer the long-standing question about the origin of cosmic rays ~100 telescopes, 2-arrays (in southern & northern hemisphere) Standard detectors will be PMTs SiPM: future candidate sensor Candidate lightsensors for CTA Matthias Kurz Max-Planck-Institut for Physics in Munich for Very High Energy Ground-Based  -ray Astronomy

3. Estimated need ~ 1.5 x 10 5 PMTs Very high Quantum Efficiency Almost 100 % Collection Efficiency of photo electrons (ph.e.) from photo cathode on the 1 st dynode Afterpulsing rate: < 0.02 % for threshold ≥ 4 ph.e. (needed for obtaining a very low threshold setting) Pulse width: < 2 - 3 ns Transit Time Spread: ≤ 1.3 ns (single ph.e.) Stabilize photo cathode to 1 st dynode to ~ 375 V Linear Dynamic Range > 5000 ph.e. About 2 years ago started a PMT development program with Hamamatsu (Japan) and Electron Tubes Enterprises (England) for the CTA project Candidate lightsensors for CTA Matthias Kurz Max-Planck-Institut for Physics in Munich Needs of light sensors for the CTA project afterpulsing event induced pulse

4. Candidate lightsensors for CTA Matthias Kurz Max-Planck-Institut for Physics in Munich Full-automatic QE measuring device Light source (Deuterium and Tungsten lamp) Monochromator Filter wheel (eliminate the second harmonics)

5. Quantum Efficiency measurements for tested PMTs Candidate lightsensors for CTA Matthias Kurz Max-Planck-Institut for Physics in Munich 1 ½ inch PMT has been chosen as the target PMT for all 3 types of telescopes CompanyType QE peak ( ) Cher Hamamatsu8619 1“ 28,7 ± 2,2 (390 nm) 19,4 ± 0,3 Hamamatsu9420 1,5“ 34,6 ± 3,1 (370 nm) 22,9 ± 0,4 Hamamatsu7724 2“ 38,9 ± 3,3 (370 nm) 25,7 ± 0,4 Electron Tubes 9117B 1,5“ 34,0 ± 3,2 (360 nm) 19,9 ± 0,3 Electron Tubes 9142B 1,125“ 30,2 ± 2,7 (370 nm) 16,5 ± 0,3

6. Candidate lightsensors for CTA Matthias Kurz Max-Planck-Institut for Physics in Munich Main candidates Hamamatsu R9420 modified (convex input window shape) (mat and polished input window types) Hamamatsu R8619 modified Body of R9420 but used 8619 dynode system (again, two window types) Electron Tubes 9117B 1.5’ size, super-bialkali photo cathode PMTs

7. Afterpulsing rates of possible candidate PMTs Candidate lightsensors for CTA Matthias Kurz Max-Planck-Institut for Physics in Munich requirement of CTA: AP rate for a threshhold ≥ 4 phe must be < 0.02 % (red line) Hamamatsu R9420 standard R9420 MOD 1 st modification R8619 MOD 1 st modification body of R9420 Hamamatsu R8619 standard Electron Tubes 9142B

8. Candidate lightsensors for CTA Matthias Kurz Max-Planck-Institut for Physics in Munich AP arrival time to check, what are the sources for AP inside PMT Peaks locate ions (H +,He +,2+, CH 4 + ) smeared out continuum below the peaks caused by rest gases (low  ”clean” vacuum) ET tube 9142B (top right) has very low AP with little peaks AP sources Varies for different PMTs ! Electron Tubes 9142B Hamamatsu R9420 standard and modified Hamamatsu 8619 standard and modified

9. Candidate lightsensors for CTA Matthias Kurz Max-Planck-Institut for Physics in Munich PMT Glowing Glowing seen from the frontglowing seen from the side Shooting pulsed laser with 40 MHz, l = 405nm CCD exposure 10 min., filter cutting l < 500nm High voltage of PMT applied Relatively high laser intensity Some evidence that it is fluorescent light emission with spectrum > 700 nm Optical afterpulsing

10. New SiPMs from MEPhI – MPI – with the help of PEI Candidate lightsensors for CTA Matthias Kurz Max-Planck-Institut for Physics in Munich Different samples: different pixel sizes, p over n type SiPMs of (1 & 3 mm²) Operation voltages 26V and 35V in total 18 different modifications of SiPMs Also tested Hamamatsu MPPCs, 1& 3mm, S10362-11-50U Also planning to test other types when available e.g. Philips, and other manufactures

11. Candidate lightsensors for CTA Matthias Kurz Max-Planck-Institut for Physics in Munich MEPhI-MPI-PEI W24-3_50B Hamamatsu S10362-11-050U Fast peak FWHM~2.5 ns and ~350ns long low-amplitude exponential tail. Tail should be taken into account for correct gain estimation of SiPM: in the fast peak only 10% of the charge in the long tail 90% of the charge Cooled down to decrease the dark noise Cut out the AP and dark rate pile up Fast pulse FWHM~2.5ns Pulse shape of different SiPMs

12. Candidate lightsensors for CTA Matthias Kurz Max-Planck-Institut for Physics in Munich Ulbricht sphere for PDE measurement Ø = 10.5 cm, made of Spectralon (highly reflective and defuse scattering material) every port provides the same amount of light (more than 100 reflections before exiting)

13. Candidate lightsensors for CTA Matthias Kurz Max-Planck-Institut for Physics in Munich Test of PDE of SiPMs PDE = photon detection efficiency Test PDE for an over- voltage of ~ 4-10% (just for testing and fine-tuning the setup) Measurements from MEPhI samples shown for an overvoltage of 15% that they can reach a peak PDE of more than 35% PDE(λ) = G Geiger-Eff.. A Geometrical-Eff.. T Transmission-Eff. QE Internal

14. - No trenches yet - With trenches (currently under production) X-talk = X-talk/5-10, i.e. expected X-talk: Candidate lightsensors for CTA Matthias Kurz Max-Planck-Institut for Physics in Munich Optical crosstalk 2-3 %

15. Candidate lightsensors for CTA Matthias Kurz Max-Planck-Institut for Physics in Munich PMT development for the needs of CTA is in progress Already now the PMTs of Hamamatsu came rather close to the specified target parameter values: peak PDE 34-35%, afterpulsing slightly above 0.02%. Next two years further optimization of PMTs from both Hamamatsu and Electron Tubes Enterprises (CTA financial support) Design and tests of PMT-based pixels and clusters of 7-pixels SiPMs are becoming serious sensor candidates for the CTA project. Intending to evaluate all candidate sensors We believe in a few years one can have high quality SiPMs from several manufacturers that can be used also in our project Conclusion

16. Candidate lightsensors for CTA Matthias Kurz Max-Planck-Institut for Physics in Munich Thank you for your attention!

17. Back up slides Candidate lightsensors for CTA Matthias Kurz Max-Planck-Institut for Physics in Munich

18. Pulse width dependence on the applied HV Supply voltage [V] FWHM [ns] e.g. : Hamamatsu 9420 VoltageFWHM [ns] 700 3,11 800 2,82 900 2,60 1000 2,64 1100 2,52 1200 2,35 ~ 82/sqrt(HV)

19. Candidate lightsensors for CTA Matthias Kurz Max-Planck-Institut for Physics in Munich PMT Glowing lower left photo: seen from top top right photo: glowing seen from side Shooting pulsed laser with 40 MHz,  = 405nm CCD exposure 10 min., filter cutting < 500nm High voltage of PMT applied Relatively high laser intensity Some evidence that it is fluorescent light emission with spectrum > 700 nm Optical afterpulsing Simple photo of PMT Light emission picture Overlay to visualize the origin of the light

20. Candidate lightsensors for CTA Matthias Kurz Max-Planck-Institut for Physics in Munich 34 - 35 % peak QE has been achieved Afterpulsing rates close to 0.02 % Intending to start a 2 years development contract with Hamamatsu and ETE, financial support promised from CTA Obtained 10 PMTs of this production from Hamamatsu for evaluating (the ones in blue-green colour) Recent progress of Hamamatsu PMTs