LENA Photosensor R&D Marc Tippmann Lothar Oberauer, Michael Wurm, Gyorgy Korga, Quirin Meindl, Michael Nöbauer, Thurid Mannel, Martin Zeitlmair, German Beischler Technische Universität München DPG-Frühjahrstagung 2011, Karlsruhe 2011/03/31

Overview LENA photosensor requirementsPMT characterization Measurements at the Laboratori Nazionali del Gran Sasso Outlook Munich test stand Optical module development Summary

LENA photosensor requirements

LENA photosensor requirements: Overview Desired energy resolution for low energies: → Light yield ≥ 200 photoelectrons/MeV → 30% optical coverage → 3000m² effective photosensitive area needed → Current standard configuration: Liquid scintillator detector: 63,000 PMTs (8“) with Winston Cones (area ×1.75) Water cherenkov muon veto: 6,000 PMTs (8“) 1/9

Timing TTS (spe, FWHM)<3.0ns Early pulses<1% Late pulses<4% LENA photosensor requirements: List 2/9

Timing TTS (spe, FWHM)<3.0ns Early pulses<1% Late pulses<4% LENA photosensor requirements: List Photo detection efficiency PDE for λ peak =420nm>20% Dynamic rangespe – 0.3pe/cm² 2/9

Michael Wurm, TUM, LENA - PMm² meeting 07/04/2009 LENA photosensor requirements: List Noise (for PMTs) Gain>3∙10 6 spe p/V>2 Dark count per area<15Hz/cm² Ionic afterpulses ( μs)<5% Fast afterpulses (5-100 ns)<5% Timing TTS (spe, FWHM)<3.0ns Early pulses<1% Late pulses<4% Photo detection efficiency PDE for λ peak =420nm>20% Dynamic rangespe – 0.3pe/cm² 2/9

LENA photosensor requirements: List Teresa Marrodán, PhD thesis Timing TTS (spe, FWHM)<3.0ns Early pulses<1% Late pulses<4% Photo detection efficiency PDE for λ peak =420nm>20% Dynamic rangespe – 0.3pe/cm² Noise (for PMTs) Gain>3∙10 6 spe p/V>2 Dark count per area<15Hz/cm² Ionic afterpulses ( μs)<5% Fast afterpulses (5-100 ns)<5% Photon Fast afterpulse 2/9

LENA photosensor requirements: List Teresa Marrodán, PhD thesis Environmental properties Pressure resistance>10bar 238 U content<3∙10 -8 g/g 232 Th content<1∙10 -8 g/g nat K content<2∙10 -5 g/g Detector lifetime>30yrs Timing TTS (spe, FWHM)<3.0ns Early pulses<1% Late pulses<4% Photo detection efficiency PDE for λ peak =420nm>20% Dynamic rangespe – 0.3pe/cm² Noise (for PMTs) Gain>3∙10 6 spe p/V>2 Dark count per area<15Hz/cm² Ionic afterpulses ( μs)<5% Fast afterpulses (5-100 ns)<5% 2/9

Fast afterpulses (fAP): Ongoing measurements of fAP time distribution for candidate PMT series → Investigate causes Currently studying their influence on the efficiency of the p decay coincidence: Bachelor thesis by Thurid Mannel Possible methods of discrimation from photons? Bachelor thesis by Martin Zeitlmair LENA photosensor requirements 3/9

PMT characterization

Borexino PMT testing facility Pulsed ps laser diode light source: 410nm, light pulse FWHM <30ps Total time resolution <140ps Can measure up to 32 PMTs simultaneously Measure transit time distribution (TDC), fast + ionic afterpulse time distribution (MTDC), charge spectrum (ADC) Measurements at the LNGS, Gran Sasso Measured 1 sample each of: Hamamatsu: R6091(3“), R6594(5“), R5912(8“) and R7081(10“) ETEL: 9351(8“) 4/9

5“ 10“ : R6594 vs. R7081 R6594 (5“)R7081 (10“) Voltage+1670V+1520V Gain1.0∙ ∙10 7 Photoelectrons (pe) per trigger 5.53%2.91% Threshold0.2pe TTS (FWHM) (Hamamatsu) 1.91ns (1.5ns) 3.05ns (3.5ns) Early pulses (all non-gaussian) 2.95%0.57% Late pulses (after photon pulse peak) 3.13%3.09% 5/9

: R6594 vs. R7081 R6594 (5“)R7081 (10“) Voltage+1670V+1520V Gain1.0∙ ∙10 7 Photoelectrons (pe) per trigger 5.53%2.91% Threshold0.2pe TTS (FWHM) (Hamamatsu) 1.91ns (1.5ns) 3.05ns (3.5ns) Early pulses (all non-gaussian) 2.95%0.57% Late pulses (after photon pulse peak) 3.13%3.09% Dark count(5.23kHz)2.64kHz Dark count per area (46.3 Hz/cm²) 5.26 Hz/cm² Ionic afterpulses0.94%5.12% 5/9

: R6594 vs. R7081 R6594 (5“)R7081 (10“) Voltage+1670V+1520V Gain1.0∙ ∙10 7 Photoelectrons (pe) per trigger 5.53%2.91% Threshold0.2pe TTS (FWHM) (Hamamatsu) 1.91ns (1.5ns) 3.05ns (3.5ns) Early pulses (all non-gaussian) 2.95%0.57% Late pulses (after photon pulse peak) 3.13%3.09% Dark count(5.23kHz)2.64kHz Dark count per area (46.3 Hz/cm²) 5.26 Hz/cm² Ionic afterpulses0.94%5.12% Peak-to-valley ratio /9

LNGS: Results Parameters + Constraints R6091 (3“) with 1.8“ aperture R6594 (5“) R5912 (8“) R7081 (10“) ETL9351 (8“) no ETL9351 (8“) average Voltage+1760V+1670V+1425V+1520V+1500V≈+1450V Gain1.0∙ ∙ ∙10 7 pe/trigger (npe)2.21%5.53%1.83%2.91%4.78%5.19% TTS (FWHM) <3.0ns (manufacturer) 1.89ns (2.0ns) 1.91ns (1.5ns) 2.04ns (2.4ns) 3.05ns (3.5ns) 2.16ns2.76ns EP (all nongauss.) <1%0.14%2.95%1.93%0.57%1.23%0.75% (3σ) LP (after PP peak) <4%6.26%3.13%2.88%3.09%4.08%7.90% (3σ) DN0.192kHz(5.23kHz)1.62kHz2.64kHz1.72kHz2.48kHz DN/area <15Hz/cm²12.1 Hz/cm²(eff.) (46.3 Hz/cm²) 5.1 Hz/cm² 5.3 Hz/cm² 7.7 Hz/cm² Ionic AP < 5%0.14%0.94%6.62%5.12%2.57%4.9% p/V > At the moment no conclusive decision possible: Need to measure ≈ 10 PMTs/series and determine limits + implications on physics from simulations 6/9

Outlook

Outlook: Munich photosensor test stand FADC: Acqiris DC282, 10bit, 8 GHz Light sources: Pulsed ps diode laser: Edinburgh Instruments EPL-405-mod, 403nm, pulse width 48ps Fast LED driven by avalanche diode: 430nm, time jitter (FWHM) <≈1ns Currently being set up Done: Light sources implemented and working, electronics running Next steps: include fiber and beam widening optics, finish online analysis software based on Labview Plan to study: PMTs: time distribution, fast AP, ionic AP, pulse shape, dynamic range, surface scans; also SiPMs 7/9

Outlook: Optical module development Light Concentrators (Winston Cones) MC simulations of light concentrators with geant4 Incorporate results into optical model of detector (geant4 MC) → determine optimum light concentrator Build prototype + scan with laser over aperture and incident angles Diploma thesis by Michael Nöbauer Pressure encapsulations Design pressure encapsulations with FEM pressure simulation, e.g. spherical shape or conical shape, integrate Winston Cones + Mu-metal shielding into design Build + test prototypes Bachelor thesis by German Beischler Borexino Winston Cone 8/9

Summary Approximate limits on photosensor properties known → do simulations to refine values Approximate limits on photosensor properties known → do simulations to refine values Have tested promising PMT series from LNGS → repeat for more samples of Hamamatsu + ETEL PMTs in Munich Have tested promising PMT series from LNGS → repeat for more samples of Hamamatsu + ETEL PMTs in Munich Also test SiPMs and Hybrid Phototubes Also test SiPMs and Hybrid Phototubes Have started development of pressure- withstanding optical modules for PMTs incorporating Winston Cones and Mu-metal Have started development of pressure- withstanding optical modules for PMTs incorporating Winston Cones and Mu-metal 9/9