LENA Photosensor RD Marc Tippmann Lothar Oberauer Michael

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 requirements PMT characterization • Measurements at the Laboratori Nazionali del Gran Sasso Outlook • Munich test stand • Optical module development Summary

LENA photosensor requirements

LENA photosensor requirements: Overview Requirements on photo sensors • Sensor performance • Environmental properties • Availability until start of construction • Cost-performance-ratio Desired energy resolution for low energies: → Light yield ≥ 200 photoelectrons/Me. V → 30% optical coverage → 3000 m² 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

LENA photosensor requirements: List Timing TTS (spe, FWHM) <3. 0 ns Early pulses <1% Late pulses <4% 2/9

LENA photosensor requirements: List Timing TTS (spe, FWHM) <3. 0 ns Early pulses <1% Late pulses <4% Photo detection efficiency PDE for λpeak=420 nm >20% Dynamic range spe – 0. 3 pe/cm² 2/9

LENA photosensor requirements: List Timing TTS (spe, FWHM) <3. 0 ns Early pulses <1% Late pulses <4% Michael Wurm, TUM, LENA - PMm² meeting 07/04/2009 Photo detection efficiency PDE for λpeak=420 nm >20% Dynamic range spe – 0. 3 pe/cm² Noise (for PMTs) Gain >3∙ 106 spe p/V >2 Dark count per area <15 Hz/cm² Ionic afterpulses (0. 1 -200 μs) <5% Fast afterpulses (5 -100 ns) <5% 2/9

LENA photosensor requirements: List Teresa Marrodán, Ph. D thesis Timing TTS (spe, FWHM) <3. 0 ns Early pulses <1% Late pulses <4% Photo detection efficiency PDE for λpeak=420 nm >20% Dynamic range spe – 0. 3 pe/cm² Noise (for PMTs) Gain >3∙ 106 spe p/V >2 Dark count per area <15 Hz/cm² Ionic afterpulses (0. 1 -200 μs) <5% Fast afterpulses (5 -100 ns) <5% Photon Fast afterpulse 2/9

LENA photosensor requirements: List Teresa Marrodán, Ph. D thesis Timing TTS (spe, FWHM) <3. 0 ns Early pulses <1% Late pulses <4% Photo detection efficiency PDE for λpeak=420 nm >20% Dynamic range spe – 0. 3 pe/cm² Noise (for PMTs) Environmental properties Gain >3∙ 106 Pressure resistance >10 bar spe p/V >2 238 U <3∙ 10 -8 g/g Dark count per area <15 Hz/cm² 232 Th Ionic afterpulses (0. 1 -200 μs) <5% nat. K Fast afterpulses (5 -100 ns) <5% Detector lifetime content <1∙ 10 -8 g/g <2∙ 10 -5 g/g >30 yrs 2/9

LENA photosensor requirements Fast afterpulses (f. AP): Ongoing measurements of f. AP 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 3/9

PMT characterization

Measurements at the LNGS, Gran Sasso Borexino PMT testing facility • Pulsed ps laser diode light source: 410 nm, light pulse FWHM <30 ps • Total time resolution <140 ps • Can measure up to 32 PMTs simultaneously • Measure transit time distribution (TDC), fast + ionic afterpulse time distribution (MTDC), charge spectrum (ADC) Measured 1 sample each of: • Hamamatsu: R 6091(3“), R 6594(5“), R 5912(8“) and R 7081(10“) • ETEL: 9351(8“) 4/9

Measurements @LNGS: R 6594 vs. R 7081 5“ 10“ R 6594 (5“) R 7081 (10“) Voltage +1670 V +1520 V Gain 1. 0∙ 107 1. 3∙ 107 Photoelectrons (pe) per trigger 5. 53% 2. 91% Threshold 0. 2 pe TTS (FWHM) (Hamamatsu) 1. 91 ns (1. 5 ns) 3. 05 ns (3. 5 ns) Early pulses (all non-gaussian) 2. 95% 0. 57% Late pulses (after photon pulse peak) 3. 13% 3. 09% 5/9

Measurements @LNGS: R 6594 vs. R 7081 R 6594 (5“) R 7081 (10“) Voltage +1670 V +1520 V Gain 1. 0∙ 107 1. 3∙ 107 Photoelectrons (pe) per trigger 5. 53% 2. 91% Threshold 0. 2 pe TTS (FWHM) (Hamamatsu) 1. 91 ns (1. 5 ns) 3. 05 ns (3. 5 ns) Early pulses (all non-gaussian) 2. 95% 0. 57% Late pulses (after photon pulse peak) 3. 13% 3. 09% Dark count (5. 23 k. Hz) 2. 64 k. Hz Dark count per area (46. 3 Hz/cm²) 5. 26 Hz/cm² 0. 94% 5. 12% Ionic afterpulses 5/9

Measurements @LNGS: R 6594 vs. R 7081 R 6594 (5“) R 7081 (10“) Voltage +1670 V +1520 V Gain 1. 0∙ 107 1. 3∙ 107 Photoelectrons (pe) per trigger 5. 53% 2. 91% Threshold 0. 2 pe TTS (FWHM) (Hamamatsu) 1. 91 ns (1. 5 ns) 3. 05 ns (3. 5 ns) Early pulses (all non-gaussian) 2. 95% 0. 57% Late pulses (after photon pulse peak) 3. 13% 3. 09% Dark count (5. 23 k. Hz) 2. 64 k. Hz Dark count per area (46. 3 Hz/cm²) 5. 26 Hz/cm² 0. 94% 5. 12% 3. 88 3. 09 Ionic afterpulses Peak-to-valley ratio 5/9

Measurements @ LNGS: Results Parameters + Constraints R 6091 (3“) with 1. 8“ aperture R 6594 (5“) R 5912 (8“) R 7081 (10“) ETL 9351 (8“) no. 1732 ETL 9351 (8“) average Voltage +1760 V +1670 V +1425 V +1520 V +1500 V ≈+1450 V Gain 1. 0∙ 107 1. 3∙ 107 1. 0∙ 107 pe/trigger (npe) 2. 21% 5. 53% 1. 83% 2. 91% 4. 78% 5. 19% TTS (FWHM) <3. 0 ns (manufacturer) 1. 89 ns (2. 0 ns) 1. 91 ns (1. 5 ns) 2. 04 ns (2. 4 ns) 3. 05 ns (3. 5 ns) 2. 16 ns 2. 76 ns 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) 0. 192 k. Hz (5. 23 k. Hz) 1. 62 k. Hz 2. 64 k. Hz 1. 72 k. Hz 2. 48 k. Hz 12. 1 Hz/cm²(eff. ) (46. 3 Hz/cm²) 5. 1 Hz/cm² 5. 3 Hz/cm² 7. 7 Hz/cm² 0. 14% 0. 94% 6. 62% 5. 12% 2. 57% 4. 9% 2. 04 3. 88 2. 99 3. 09 2. 25 2. 10 DN DN/area <15 Hz/cm² Ionic AP < 5% p/V >2 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 DC 282, 10 bit, 8 GHz • Light sources: • Pulsed ps diode laser: Edinburgh Instruments EPL-405 -mod, 403 nm, pulse width 48 ps • Fast LED driven by avalanche diode: 430 nm, time jitter (FWHM) <≈1 ns 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; 7/9 also Si. PMs

Outlook: Optical module development Light Concentrators (Winston Cones) Borexino Winston Cone • MC simulations of light concentrators with geant 4 • Incorporate results into optical model of detector (geant 4 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 8/9

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