Attenuation Length Measurements of DUNE Prototype Light Guides Stuart Mufson, Brice Adams, Brian Baugh, Bruce Howard, Denver Whittington October 20, 2015
Several light guide technologies tested Technologies selected for next (final) TallBo run: a) acrylic light guide with waveshifter embedded in plastic (MIT) 128 nm LAr scintillation light SiPM Array 430 nm shifted light (in bar) b) commercial Eljen light guide with waveshifting plate (IU) LS Radiator (VUV → Blue) WLS bar (blue → green) 128 nm LAr scintillation light Indiana U, cartoon below y a r r A 430 nm shifted light from plate M P i S ~490 nm shifted light (in bar)
Parameters to optimize for photon detector paddle performance: • SiPM performance noise, gain, cross talk, aging characteristics discussed at last PD telecon Noise Rate @ 24.5 V, SiPMs 4-6 Cross Talk Prob @ 24.5 V, SiPMs 4-6 bias voltage = 30.5 V bias voltage = 30.5 V pulsed SiPMs shown at 200 days pulsed SiPMs shown at 200 days 100" 60" 50" 80" cross talk prob [%] noise rate [Hz] 40" 60" SiPM"4" SiPM"4" 30" SiPM"5" SiPM"5" 40" SiPM"6" 20" SiPM"6" 1.4e9"pulses" 20" 1.4e9"pulses" 10" 0" 0" 0" 50" 100" 150" 200" 250" 0" 50" 100" 150" 200" 250" # days in LN2 # days in LN2 Pulse Test: SiPM response falls (conservatively) by ~25%/100 yrs = 0.25%/yr ¡ ¡
• light guide performance - brightness of light guide - attenuation length of light guide Relative brightness of “best” two light guide technologies in last TallBo run, which includes attenuation length effects Eljen light guide + Dip-coated MIT waveshifting plate x 2 light guide 0.08 0.04 0.07 High-Front High-Front 0.035 0.06 Low-Front Low-Front 0.03 0.05 0.025 0.04 0.02 0.03 0.015 0.02 0.01 0.01 0.005 0 0 0 50 100 150 200 250 300 0 50 100 150 200 250 300 Signal [PE] Signal [PE]
TallBo dewar Light guide technologies tested TallBo Run #4, second fill • WLS Polystyrene + Acrylic Plate (TPB) • WLS Polystyrene + Acrylic Plate (bis-MSB) • WLS PVT + Acrylic Plate (TPB) • WLS PVT + Acrylic Plate (bis-MSB) • WLS Polystyrene + Fused Silica Plate (TPB) • Dip-coated Acrylic (TPB), IU design • Dip-coated Acrylic (TPB), IU design • WLS PVT + Fused Silica Plate (TPB) • WLS PVT + Acrylic Plate (TPB), double-sided • Dip-coated Acrylic (TPB), MIT design • WLS Polystyrene + Acrylic Plate (TPB), double-sided • WLS Polystyrene + Acrylic Plate (bis-MSB), double-sided Light guides in Phase 1
Independent attenuation length measurements in the IU dewar measurements of pulse height vs distance along light guide 3-day turnaround 1. light guides loaded into frame 2. dewar pumped down overnight 3. LAr fill and measurements 4. warm up second α source added 241 Am source gives monoenergetic 5.5 MeV α ’s
Analysis – plot relative measurements of pulse height as a function of distance ( ) ratio = pulse height measurement n = exp( − Δ x x attn ) ( ) pulse height measurement 1 Slope of a straight line fit to ln(ratio) is proportional to -(1/attenuation length) TallBo MIT bar Eljen Bar, fused silica plate, TPB evaportively coated attnLen = 194 cm attnLen = 205 cm 6.00" 6.00" 5.50" 5.50" y"="$0.0131x"+"4.5266" y"="$0.0124x"+"5.6996" 5.00" 5.00" ln(pe) ln(pe)' 4.50" 4.50" 4.00" 4.00" 3.50" 3.50" 3.00" 3.00" 0" 5" 10" 15" 20" 25" 30" 35" 0" 5" 10" 15" 20" 25" inches inches' (measurements give attenuation length, not relative brightness)
More sophisticated analyses are consistent with these results MIT light guide #3 Integrated Signal in Waveform vs Source Position Integrated Signal [PE] 160 140 250 120 200 100 150 80 60 100 40 50 20 0 0 0 5 10 15 20 25 30 35 Position single exponential fit, attenuation length = 29.5” -‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑-‑ ¡ MIT light guide #1 double exponential fit • short attnLen = 17.6” • long attnLen = 53.5”
Attenuation Lengths MIT Light Guides Results: 300" 250" a"enua&on(length([cm]( 200" MIT light guides: 150" variable attenuation lengths 100" 50" 0" 1" 2" 3" 4" 5" 6" 7" light(guide( Attenuation Lengths Eljen Light Guides + waveshifting disk 300" 250" a"enua&on(length([cm]( Eljen light guides: 200" consistently long attenuation 150" lengths 100" 50" 0" 1" 2" 3" 4" 5" light(guide(
Absolute “brightness” or VUV photon efficiency measurements planned at IU (Bruce Howard) Use VUV monochromator back-filled with Ar gas D 2 lamp spectrum D 2 lamp vacuum chamber: • pumped down • back-filled with Ar gas
VUV Monochromator S etup (1) Calibrate D 2 lamp NIST-calibrated grating SiPM order-sorting filter # VUV photons/cm 2 /s NIST-calibrated emitted by lamp SiPM slit stop D 2 lamp light guide, illuminated from the side, viewed from the end
VUV Monochromator S etup (1) Make measurements with calibrated photodiode NIST-calibrated grating SiPM order-sorting filter # VUV photons/cm 2 /s measured slit stop D 2 lamp light guide, illuminated from the side, viewed from the end
Summary • Next (last) TallBo test in early 2016 to include 2 technologies: - hand-dipped MIT technology - commercial light guide/waveshifting plate technology • To optimize for photon detector paddle performance - SiPM performance: noise, gain, cross talk, aging characteristics � no show stoppers so far - light guide attenuation length � variable for hand-dipped design; Eljen light guides uniformly long - light guide “brightness”, or VUV photon detection efficiency � hand-dipped design bright � wavelength shifting plate design not optimized
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