1. LOGO The VSiPMT Project Progress in the realization of a larger prototype Felicia Barbato – University of Naples “Federico II” – Italy

2. LOGO Our goal: increase the SiPM surface An innovative design for a modern hybrid photodetector based on the combination of a Silicon PhotoMultiplier (SiPM) with a hemispherical vacuum glass PMT standard envelope Photocathode Focusing Ring The classical dynode chain of a PMT is replaced with a SiPM, acting as an electron multiplying detector. SiPM Felicia Barbato PD15 - Troitsk 7/07/2015

3. LOGO Advantages The classical dynode chain of a PMT is replaced with a SiPM, acting as an electron multiplying detector. excellent photon counting high gain (>10 6 ) negligible power consumption (nW) small TTS (<ns) simplicity, compactness and robustness Felicia Barbato PD15 - Troitsk 7/07/2015

4. LOGO The industrial prototypes 32 mm 33 mm In 2013 Hamamatsu realized for us two industrial prototype, by arranging a no-windowed SiPM inside a commercial Hamamatsu HPD. The characterization of the devices pointed out features even better than expected Felicia Barbato PD15 - Troitsk 7/07/2015

5. LOGO Waveforms and spectra Excellent photon counting capability 5 mV/div 20 ns/div Peak values istogram MEASUREMENT CONDITIONS: VSiPMT illuminated by a pulsed laser light at low intensity (407nm) Oscilloscope triggered in synch with the laser Responses for multiple triggers are overlaid MEASUREMENT CONDITIONS: VSiPMT illuminated by a pulsed laser light at low intensity (407nm) Oscilloscope triggered in synch with the laser Responses for multiple triggers are overlaid Well separated waveforms Felicia Barbato PD15 - Troitsk 7/07/2015

6. LOGO Waveforms and spectra Excellent photon counting capability 5 mV/div 20 ns/div MEASUREMENT CONDITIONS: VSiPMT illuminated by a pulsed laser light at low intensity (407nm) Oscilloscope triggered in synch with the laser Responses for multiple triggers are overlaid MEASUREMENT CONDITIONS: VSiPMT illuminated by a pulsed laser light at low intensity (407nm) Oscilloscope triggered in synch with the laser Responses for multiple triggers are overlaid Felicia Barbato PD15 - Troitsk 7/07/2015

7. LOGO Work function Efficiency is highly stable over 3200 V. No need for high voltage stabilization. HV: photoelectron transfer NO power consumption (NULL current) unlike PMTs. LV-based gainEASY STABILIZATION Reducing the SiO 2 coating layer it will be possible to reach the plateau region at even lower voltages Felicia Barbato PD15 - Troitsk 7/07/2015

8. LOGO Photocathode XY scan CHARACTERISTICS: 7mm x 7mm entrance window 3 mm Ø GaAsP photocathode 1mm 2 MPPC Homogeneous efficiency ≈ 0.2 over a 7mm 2 surface Surface increase factor ≈ 7 Felicia Barbato PD15 - Troitsk 7/07/2015

9. LOGO Gain Peak values hystogram Area hystogra m Ideal Working Point: 72.2V G ≈ 6x10 6 (G AMP = 20); Dark Count ≈ 60 kcps; High gain (10 5 ÷10 6 ) Linear trend High gain (10 5 ÷10 6 ) Linear trend Total Gain = G VSiPMT x G AMP G VSiPMT @ 72.2V ≈ 3x10 5 Felicia Barbato PD15 - Troitsk 7/07/2015

10. LOGO Transit Time Spread TT  T distribution VSiPMT TTS (σ) < 0.5 ns VSiPMT spe signal Laser Trigger Felicia Barbato PD15 - Troitsk 7/07/2015

11. LOGO Dark Count Rate Decisively looks like a weak point However... High DC rates 100 – 1000 kcps Felicia Barbato PD15 - Troitsk 7/07/2015

12. LOGO Dark Count Rate New generation Hamamatsu MPPCs Felicia Barbato PD15 - Troitsk 7/07/2015

13. LOGO Dynamic range What we measured ZJ4991 (100  m) has a too limited linearity The output signal saturates soon, with N fired not exceeding 20 even under high illumination conditions robust hint for a too strong focusing small size of the photoelectrons beam robust hint for a too strong focusing small size of the photoelectrons beam Felicia Barbato PD15 - Troitsk 7/07/2015

14. LOGO Focusing Differently from the cases of a PMT or an HPD, a too strong focusing would be deleterious because a too squeezed photoelectron spot means that not all pixels are involved, thus drastically reducing the linearity. SiPM: linearity strongly related to the total number of pixels. Focusing : linearity is maximized if for a photocathode uniformly illuminated all pixels are hit by the accelerated photoelectrons. VSiPMT dynamic range depends on two factors: Felicia Barbato PD15 - Troitsk 7/07/2015

15. LOGO The characterization of the prototypes by Hamamatsu revealed that the VSiPMT is feasible and competitive The prototypes by Hamamatsu are too small and non optimized. We want to go ahead with the realization of a larger, optimized and usable prototype. Felicia Barbato PD15 - Troitsk 7/07/2015

16. LOGO We will pay a close attention on the optimization of this two parameters Thus we organized a plan in 5-phases Optimizing a prototype Felicia Barbato PD15 - Troitsk 7/07/2015

17. LOGO Work-plan Phase 5 Phase 4 Phase 1 Phase 2 Phase 3 Simulation for an optimized focusing SiPMselectionAndcharacterization Photo- cathode deposition VSiPMTassembly VSiPMTcharacterization Felicia Barbato PD15 - Troitsk 7/07/2015

18. LOGO Phase 1 Electrons emission: E=1eV α=40° Focusing ring: V=-2kV Spot: ø=3.5mm Felicia Barbato PD15 - Troitsk 7/07/2015 The photoelectron spot is supposed to be spread out over the SiPM surface to maximize the dynamic range Simulations – Photoelectron trajectories

19. LOGO Phase 2 SiPMSiPM SiPMMPPC Hamamatsu S10943-3360 (X) n.1 V bias 67.15V Gain1.25 x 10 6 Dark Count Rate≈ 400 kcps Size3x3 mm 2 Pixel Size50 µm Number of pixels3600 Felicia Barbato PD15 - Troitsk 7/07/2015 We selected a special non-windowed SiPM with a high pixel-number and a reasonable noise in order to achieve a wide dynamic range

20. LOGO Phase 2 SiPMSiPM Felicia Barbato PD15 - Troitsk 7/07/2015

21. LOGO Phase 3 We don’t have a facility able to deposit an air sensitive photocathode, so we are looking for the realization of a metallic photocathode Photocathode deposition Felicia Barbato PD15 - Troitsk 7/07/2015 We are trying to realize a homemade VSiPMT prototype by cutting a commercial PMT and preserving its photocathode

22. LOGO Phase 3 PMT cut Digging a groove by using a band saw with diamond grinding disc 3-inches PMT Cutting the PMT with an hot wire in Argon atmosphere by using a glove box (Argon 5.0) Felicia Barbato PD15 - Troitsk 7/07/2015 PRELIMINARY

23. LOGO Phase 3 PMT cut The original PMTThe PMT after the cut Felicia Barbato PD15 - Troitsk 7/07/2015 PRELIMINARY

24. LOGO Phase 3 PMT cut Felicia Barbato PD15 - Troitsk 7/07/2015 PRELIMINARY Unfortunately we succeed in maintaining only a fraction of the efficiency of the original photocathode

25. LOGO Phase 4 VSiPMT Assembly – The SiPM frame TOP VIEW BOTTOM VIEW KA KA HV GND Getters Grounded copper mask Felicia Barbato PD15 - Troitsk 7/07/2015

26. LOGO Phase 4 VSiPMT Assembly 3x3mm 2 SiPM HV tab SiPM frame Centering disc Vacuum feedthrough Felicia Barbato PD15 - Troitsk 7/07/2015 PRELIMINARY

27. LOGO Phase 4 VSiPMT Assembly Felicia Barbato PD15 - Troitsk 7/07/2015 PRELIMINARY

28. LOGO Phase 4 VSiPMT Assembly – The final product Felicia Barbato PD15 - Troitsk 7/07/2015 PRELIMINARY

29. LOGO Phase 5 Felicia Barbato PD15 - Troitsk 7/07/2015 PRELIMINARY VSiPMT Test HV=-4kV HV=OFF

30. LOGO All this features make the VSiPMT to be the answer to many big astroparticle physics experiments Felicia Barbato PD15 - Troitsk 7/07/2015 Conclusions Realize an air transportable photocathode Realize a new, optimized and larger prototype with a new company

31. LOGO