A new generation photodetector The VSiPMT Project

Our goal: increase the SiPM surface Photocathode Focusing Ring SiPM The classical dynode chain of a PMT is replaced with a SiPM, acting as an electron multiplying detector. 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 IFAE - Roma 10/04/2015 Felicia Barbato

Advantages The classical dynode chain of a PMT is replaced with a SiPM, acting as an electron multiplying detector. excellent photon counting high gain (>106) negligible power consumption (nW) small TTS (<ns) simplicity, compactness and robustness IFAE - Roma 10/04/2015 Felicia Barbato

Advantages The classical dynode chain of a PMT is replaced with a SiPM, acting as an electron multiplying detector. Thanks to the SiPM the photon counting capability of the whole device will be improved with respect to a classical PMT excellent photon counting high gain (>106) negligible power consumption (nW) small TTS (<ns) simplicity, compactness and robustness IFAE - Roma 10/04/2015 Felicia Barbato

Advantages The classical dynode chain of a PMT is replaced with a SiPM, acting as an electron multiplying detector. excellent photon counting The BIGGEST DIFFERENCE with respect to classical HPDs high gain (>106) negligible power consumption (nW) In a VSiPMT the high gain is obtained by the electrons crossing the Geiger region of the SiPM. Thus we need to supply a fair HV, only to obtain electrons with the right energy to enter in the silicon bulk small TTS (<ns) simplicity, compactness and robustness A new generation photodetector for astroparticle physics: the VSiPMT, G. Barbarino et al., DOI: 10.1016/j.astropartphys.2015.01.003 IFAE - Roma 10/04/2015 Felicia Barbato

Advantages The classical dynode chain of a PMT is replaced with a SiPM, acting as an electron multiplying detector. excellent photon counting high gain (>106) The absence of the voltage divider leads to a much lower power consumption negligible power consumption (nW) small TTS (<ns) simplicity, compactness and robustness GREAT DEAL for such experiments operating in hostile environments (underwater, ice, space) IFAE - Roma 10/04/2015 Felicia Barbato

Advantages In the VSiPMT the dynode chain is replaced by a SiPM, thus for such a device the TTS is simply due to the electron trajectories between the photocathode and the SiPM and so we sistematically expect a lower TTS with respect to a classical PMT. The classical dynode chain of a PMT is replaced with a SiPM, acting as an electron multiplying detector. excellent photon counting high gain (>106) negligible power consumption (nW) The TTS is smaller for the VSiPMT than for a standard PMT. small TTS (<ns) simplicity, compactness and robustness IFAE - Roma 10/04/2015 Felicia Barbato

Advantages The classical dynode chain of a PMT is replaced with a SiPM, acting as an electron multiplying detector. excellent photon counting high gain (>106) negligible power consumption (nW) Thanks to the absence of the dynode chain the VSiPMT will be more compact and simpler having only 3 output connections: HV, SiPM bias voltage and the output signal. small TTS (<ns) simplicity, compactness and robustness IFAE - Roma 10/04/2015 Felicia Barbato

The first industrial prototypes An overview on The first industrial prototypes

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 IFAE - Roma 10/04/2015 Felicia Barbato

Well separated waveforms Excellent photon counting capability Waveforms and spectra 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 Well separated waveforms 5 mV/div 20 ns/div Excellent photon counting capability IFAE - Roma 10/04/2015 Felicia Barbato

Excellent photon counting capability Waveforms and spectra 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 20 ns/div Excellent photon counting capability 5 mV/div IFAE - Roma 10/04/2015 Felicia Barbato

Work function HV: photoelectron transfer NO power consumption (NULL current) unlike PMTs. LV-based gain EASY STABILIZATION Reducing the SiO2 coating layer it will be possible to reach the plateau region at even lower voltages Efficiency is highly stable over 3200 V. No need for high voltage stabilization. IFAE - Roma 10/04/2015 Felicia Barbato

Surface increase factor ≈ 7 Photocathode XY scan CHARACTERISTICS: 7mm x 7mm entrance window 3 mm Ø GaAsP photocathode 1mm2 MPPC Homogeneous efficiency ≈ 0.2 over a 7mm2 surface Surface increase factor ≈ 7 IFAE - Roma 10/04/2015 Felicia Barbato

Total Gain = GVSiPMT x GAMP Peak values hystogram High gain (105÷106) Linear trend Area hystogram Total Gain = GVSiPMT x GAMP Ideal Working Point: 72.2V G ≈ 6x106 (GAMP = 20); Dark Count ≈ 60 kcps; GVSiPMT @ 72.2V ≈ 3x105 IFAE - Roma 10/04/2015 Felicia Barbato

Transit Time Spread Laser Trigger DT distribution DT VSiPMT spe signal DT VSiPMT TTS (σ) < 0.5 ns DT distribution IFAE - Roma 10/04/2015 Felicia Barbato

Decisively looks like a weak point Dark Count Rate High DC rates 100 – 1000 kcps Decisively looks like a weak point However... IFAE - Roma 10/04/2015 Felicia Barbato

New generation Hamamatsu MPPCs Dark Count Rate New generation Hamamatsu MPPCs IFAE - Roma 10/04/2015 Felicia Barbato

ZJ4991 (100mm) has a too limited linearity Dynamic range What we measured robust hint for a too strong focusing small size of the photoelectrons beam ZJ4991 (100mm) has a too limited linearity The output signal saturates soon, with Nfired not exceeding 20 even under high illumination conditions IFAE - Roma 10/04/2015 Felicia Barbato

VSiPMT dynamic range depends on two factors: Focusing VSiPMT dynamic range depends on two factors: 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. 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. IFAE - Roma 10/04/2015 Felicia Barbato

Realization of a larger VSiPMT A new project for the Realization of a larger VSiPMT

Optimizing a prototype We will pay a close attention on the optimization of this two parameters VSiPMT Main aspects Focusing optimization SiPM selection Thus we organized a plan in 5-phases IFAE - Roma 10/04/2015 Felicia Barbato

How we expect the VSiPMT to be Photocathode How we expect the VSiPMT to be Focusing metallic ring SiPM SiPM frame HV Tab Feedthrough IFAE - Roma 10/04/2015 Felicia Barbato

Simulation for an optimized focusing Work-plan Phase 5 Phase 4 Phase 1 Phase 2 Phase 3 SiPM selection And characteri zation Simulation for an optimized focusing VSiPMT characteri zation PMT cut VSiPMT assembly IFAE - Roma 10/04/2015 Felicia Barbato

Simulation for an optimized focusing Phase 1 Phase 1 Simulation for an optimized focusing The prototypes by Hamamatsu showed a linearity range much lower than expected Focusing the photoelectrons in a wider spot will help to damp the problem IFAE - Roma 10/04/2015 Felicia Barbato

Phase 1 Simulations Equipotential surfaces inside the VSiPMT. Electroctatic potential distribution inside the VSiPMT. IFAE - Roma 10/04/2015 Felicia Barbato

Electron trajectories Phase 1 Simulations Electrons emission: E=1eV α=40° Focusing ring: V=-1.95kV d=18mm Spot: ø=3mm Timing: TT=7.01ns TTS=0.60ns Electron trajectories IFAE - Roma 10/04/2015 Felicia Barbato

Phase 2 Phase 2 SiPM selection And characteri zation The prototypes by Hamamatsu showed a linearity range much lower than expected We selected a special non-windowed SiPM with a high pixel-number and a reasonable noise in order to achieve a wide dynamic range IFAE - Roma 10/04/2015 Felicia Barbato

Phase 2 SiPM SiPM MPPC Hamamatsu S10943-3360 (X) n.1 V bias 67.15V Gain 1.25 x 106 Dark Count Rate ≈ 400 kcps Size 3x3 mm2 Pixel Size 50 µm Number of pixels 3600 IFAE - Roma 10/04/2015 Felicia Barbato

Phase 2 SiPM IFAE - Roma 10/04/2015 Felicia Barbato

Why cutting a PMT? Phase 3 Phase 3 PMT cut We want to realize a larger prototype We have time requirements that the collaboration with Hamamatsu can not satisfy We are not able to deposit a photocathode, so we tried to cut a commercial PMT preserving its photocathode 1 2 3 IFAE - Roma 10/04/2015 Felicia Barbato

Phase 3 PRELIMINARY PMT cut Carried out in Argon gas (5.0 pure) 3-inches PMT Band saw with diamond grinding disc IFAE - Roma 10/04/2015 Felicia Barbato

Phase 3 PRELIMINARY PMT cut The original PMT The PMT after the cut Unfortunately we succeed in maintaining only a fraction of the original photocathode IFAE - Roma 10/04/2015 Felicia Barbato

Phase 4 Phase 4 VSiPMT assembly After the cut (still in Argon gas) we assemble the device by substituting a SiPM mounted on a PCB frame. IFAE - Roma 10/04/2015 Felicia Barbato

VSiPMT Assembly – The SiPM frame Phase 4 VSiPMT Assembly – The SiPM frame K A HV K A Getters GND Grounded copper mask TOP VIEW BOTTOM VIEW IFAE - Roma 10/04/2015 Felicia Barbato

Phase 4 PRELIMINARY VSiPMT Assembly HV tab SiPM frame 3x3mm2 SiPM Vacuum feedthrough Centering disc IFAE - Roma 10/04/2015 Felicia Barbato

Phase 4 PRELIMINARY VSiPMT Assembly IFAE - Roma 10/04/2015 Felicia Barbato

VSiPMT Assembly – The final product Phase 4 VSiPMT Assembly – The final product PRELIMINARY IFAE - Roma 10/04/2015 Felicia Barbato

Conclusions

Why should we realize a larger VSiPMT? The VSiPMT key words Photon counting capability Low power consumption Large sensitive surface Good timing performances (low TTS) High stability (not depending on HV) All this features make the VSiPMT to be the answer to many big astroparticle physics experiments IFAE - Roma 10/04/2015 Felicia Barbato

We hope to succeed by the end of the year The idea Start Proof of feasibility Proof First prototype Prototype 3-in prototype 3-inches 2007 2012 2013 2015 We hope to succeed by the end of the year We are here IFAE - Roma 10/04/2015 Felicia Barbato

Thank You !

Why we should choose the VSiPMT? Features PMT VSiPMT Comparison Efficiency QEphotocathodex ε1dynode(0.8) QEphotocathodex FillFactor(twd 1) ≈equivalent Gain 106 - 107 105 - 106 Timing ns Fraction of ns (no dynode spread) Linearity Depending on gain Depending on #cells Power Consumption Divider Dissipation VSiPMT: No dissipation Amp. (G=10-20): <5mW Power Supply Stability HV Stabilization LV easy stabilization Dark counts rate (new) ≈ kHz @ 0.5pe ≈ few kHz @0.5pe ≈equivalent (today) Photon Counting Difficult Excellent Afterpulse (new) ≈10% @0.5pe <0,3% @0.5pe VSiPMT (today) Peak-to-valley ratio ≈3 >60 IFAE - Roma 10/04/2015 Felicia Barbato