ArCLight is a novel device for detecting scintillation light over large areas
with Photon Detection Efficiency (PDE) of the order of a few percent. Its
robust technological design allows for efficient use in large-volume particle
detectors, such as Liquid Argon Time Projection Chambers (LArTPCs) or liquid
scintillator detectors. Due to its dielectric structure it can be placed inside
volumes with high electric field. It could potentially replace vacuum
PhotoMultiplier Tubes (PMTs) in applications where high PDE is not required.
The photon detection efficiency for a 10x10cm2 detector prototype was measured
to be in the range of 0.8% to 2.2% across the active area

Auger, M.

Chen, Y.

Ereditato, A.

Goeldi, D.

Kreslo, I.

Lorca, D.

Luethi, M.

Mettler, T.

Sinclair, J. R.

Weber, M. S.

English

arXiv

ArgonCube Light readout system (ArCLight) is a novel device for detecting scintillation light over large areas with Photon Detection Efficiency (PDE) of the order of a few percent. Its robust technological design allows for efficient use in large-volume particle detectors, such as Liquid Argon Time Projection Chambers (LArTPCs) or liquid scintillator detectors. Due to its dielectric structure it can be placed inside volumes with high electric field. It could potentially replace vacuum PhotoMultiplier Tubes (PMTs) in applications where high PDE is not required. The photon detection efficiency for a 10 × 10 cm2 detector prototype was measured to be in the range of 0.8% to 2.2% across the active area.</jats:p

Martin Auger

Yifan Chen

Antonio Ereditato

Damian Goeldi

Igor Kreslo

David Lorca

Matthias Luethi

Thomas Mettler

James Sinclair

Michele Weber

Crossref

Instruments

ArCLight—A Compact Dielectric Large-Area Photon Detector

Auger, Martin

Chen, Yifan

Ereditato, Antonio

Göldi, Damian

Kreslo, Igor

Lorca, David

Lüthi, Matthias

Mettler, Thomas

Sinclair, James

Weber, Michele

Bern Open Repository and Information System (BORIS)

instrumentsArticleArCLight—A Compact Dielectric Large-AreaPhoton DetectorMartin Auger, Yifan Chen, Antonio Ereditato ID , Damian Goeldi ID , Igor Kreslo *,David Lorca ID , Matthias Luethi, Thomas Mettler, James Sinclair and Michele Weber IDLaboratory for High Energy Physics, Albert Einstein Center for Fundamental Physics, Universität Bern,3012 Bern, Switzerland; martin.auger@lhep.unibe.ch (M.A.); Yifan.Chen@lhep.unibe.ch (Y.C.);antonio.ereditato@lhep.unibe.ch (A.E.); damian.goeldi@lhep.unibe.ch (D.G.); david.lorca@lhep.unibe.ch (D.L.);matthias.luethi@lhep.unibe.ch (M.L.); Thomas.Mettler@lhep.unibe.ch (T.M.); james.sinclair@lhep.unibe.ch (J.S.);michele.weber@lhep.unibe.ch (M.W.)* Correspondence: Igor.Kreslo@cern.chReceived: 1 December 2017; Accepted: 2 Feburay 2018; Published: 6 Feburay 2018Abstract: ArgonCube Light readout system (ArCLight) is a novel device for detecting scintillationlight over large areas with Photon Detection Efficiency (PDE) of the order of a few percent. Its robusttechnological design allows for efficient use in large-volume particle detectors, such as LiquidArgon Time Projection Chambers (LArTPCs) or liquid scintillator detectors. Due to its dielectricstructure it can be placed inside volumes with high electric field. It could potentially replace vacuumPhotoMultiplier Tubes (PMTs) in applications where high PDE is not required. The photon detectionefficiency for a 10× 10 cm2 detector prototype was measured to be in the range of 0.8% to 2.2% acrossthe active area.Keywords: scintillation; liquid argon; photo-detectors1. IntroductionModern detectors for neutrino oscillation physics are, to a large extent, represented by LiquidArgon Time Projection Chambers (LArTPCs). At Laboratory for High Energy Physics (LHEP),University of Bern, an extensive LArTPC R&D program is ongoing since 2007. Our findings from thisresearch program [1–3] brought us to the ArgonCube project [4]. ArgonCube, a modular single-phaseLAr TPC, is a leading contender for the LAr component of the Deep Underground Neutrino Experiment(DUNE) near detector complex [5]. The function of the ArgonCube Light readout system (ArCLight) isto detect and quantify parameters of the prompt scintillation light, to provide t0 for the TPC, and giveadditional information on deposited energy.One of the assets of the ArgonCube design is its extremely low fraction of insensitive argonvolume (below 10%). This applies strict limit to the volume that a light readout system can occupy,as well as its arrangement inside the detector. Classic vacuum PMT-based light readout systemsrequire much larger volumes occupied by PMTs, located on low-potential side of the TPC. Such asolution is not compatible with the modular design of ArgonCube, where the TPC modules standside-by-side and any additional space between them degrades tracking and calorimetric performanceof the detector as a whole.One more specialty of LAr scintillation is its short wavelength: its emission spectrum peaks at128 nm. This spectrum is usually first shifted towards the visible range with a wavelength shifter (WLS),for which 1,1,4,4-tetraphenyl-1,3-butadiene (TPB) is a commonly used material. Strictly speaking,the process of converting 128 nm photons to visible ones (430 nm for TPB) is closer to scintillationthan to fluorescence, because of the high energy of the initial photons. Absorption of these photonsInstruments 2018, 2, 3; doi:10.3390/instruments2010003 www.mdpi.com/journal/instrumentsInstruments 2018, 2, 3 2 of 8may lead to photo-ionization and dissociation rather than just excitation. This explains why the TPBconversion efficiency for LAr scintillation spectrum exceeds unity [6].Several interesting low-volume large-area solutions have been investigated by the detector designcommunity in order to meet the requirements of detecting LAr scintillation light [7–13]. However, thesesolutions are based on full reflection from the interface between a polymer and surrounding LAr,which is limited by the small difference in the refractive index. In the case of organic liquid scintillatoras detector medium, this difference may practically vanish, rendering such solutions useless.The design of ArCLight was inspired by the ARAPUCA light trap sensor [14]. The ARAPUCAfunctions by trapping photons inside a cavity with highly reflective internal surfaces. After conversionto blue region with the first WLS, LAr scintillation light enters the cavity through a dichroic film.A second WLS coats the inner surface of the film. The latter shifts the wavelength beyond thetransparent cutoff of the dichroic film, trapping the light within the cavity. ArCLight employs a similarprinciple, with the cavity void replaced by a solid transparent polymer sheet doped with a WLS dye.This improvement makes the detector substantially more robust, compact and stable, especially whenscaling up to large areas.2. Detector DesignAn ArCLight prototype with a 10×10 cm2 active area (98% of total area) is shown in Figure 1.Figure 1. ArgonCube Light (ArCLight) 10× 10 cm2 prototype. Four silicon photomultipliers (SiPMs)in surface mount device (SMD) packages can be seen at the lower side, soldered to a narrow printedcircuit board (PCB) which provides SMD coaxial connectors for signal readout. The rest of the sensorarea is dielectric.The structure of the device is shown in Figure 2. It is composed of a 4 mm thick EJ280 WLS(http://www.eljentechnology.com/products/wavelength-shifting-plastics/ej-280-ej-282-ej-284-ej-286) plate, with reflective films laminated to each side. The back face and edges are covered with adielectric specular reflector foil (VM2000, former name for Vikuiti ESR, 3M Inc., St. Paul, MN, USA),which has ≈98% reflectance for the visible light spectrum [15]. The front face is coated with a dichroicmirror (DF-PA Chill, 3M Inc., St. Paul, MN, USA) film that is transparent in the blue and has highreflectance in the green range of the spectrum.Spectral characteristics of the dichroic film are measured for two incidence angles: 0◦ and 45◦ with aspectrophotometer (LAMBDATM 750 UV/Vis/NIR spectrophotometer, PerkinElmer). Typically, the cutoffwavelength of the dichroic mirror behaves as λ = λ0√1− (sin α/n)2, where α is an incidence angle andInstruments 2018, 2, 3 3 of 8n is the effective refraction index of the structure. This allows interpolation of measured spectra for anglesbetween 0◦ and 45◦. Both films are held in place by thin layers of transparent adhesive. In a version aimedfor use in LAr, an additional layer of TPB WLS is deposited on the front face to convert the scintillationlight into the blue wavelength [16]. At one edge of the WLS plate four Hamamatsu S13360-3050VE(http://www.hamamatsu.com/us/en/product/category/3100/4004/4113/S13360-3050PE/index.html) Silicon Photo-Multipliers (SiPMs) are mounted, each with a 3 × 3 mm2 sensitive area.Photons in the spectral range of 400–450 nm pass through the dichroic reflector at the front face(Figure 3) and are efficiently absorbed by WLS (Figure 4). The latter re-emits them in green with aspectral maximum of 490 nm, as shown in Figure 5 (WLS spectral parameters are taken from [17]).These photons get trapped inside the WLS volume since the reflection coefficient of the dichroicfilm reaches 98% for large incidence angles at this wavelength, as shown in Figure 5. About 30% ofthe emitted light (below ∼10◦ incidence) is therefore lost. However, due to specular reflectance ofthe mirror films, photons that are reflected once stay captured inside the WLS volume. Eventually,the photons reach openings in the side mirrors, where they are detected by the SiPMs. The emissionspectrum of the WLS plastic matches the spectral sensitivity of the SiPMs [18] closely, as shown inFigure 6.Figure 2. The ArCLight light collector cross section near the corner. Structure is mechanically supportedby 4-mm thick wavelength shifter (WLS) plastic (EJ-280) plate. Front side is covered with dichroicmirror film (3M DF-PA Chill) and the first WLS layer (TPB). At the back side 3M Vikuiti EnhancedSpecular Reflector is attached. Two out of four SiPMs (Hamamatsu S13360-3050VE) soldered to theircarrier PCB are also shown, separate from the light collector.Figure 3. TPB emission spectrum [16] (in a.u.) and the dichroic mirror transparency overlap forincidence angle within the range of 0 to 45 degrees.Instruments 2018, 2, 3 4 of 8Figure 4. TPB emission spectrum [16] and WLS absorption spectrum [17] (both in a.u.) are well matched.Figure 5. WLS emission spectrum [17] (in a.u.) and the dichroic mirror reflectance fully overlap forangles above certain value between 0 and 45 degrees, and partially below. About 30% of the emittedlight is lost.Figure 6. Spectral relationships: WLS emission spectrum [17] (in a.u.) and SiPM spectral dependence of PDE [18].Instruments 2018, 2, 3 5 of 8The expected PDE is calculated by folding the individual efficiencies at each step ofphoton transport:QPDE =12εTPB T425 εWLS εSA εcoll εSiPM (1)12 εTPB represents the efficiency of converting photons from 128 nm to 425 nm [6], taking into accountthe 2pi solid angle acceptance (to one side only). T425 is the average transparency of the dichroic filteraround 425 nm. εWLS is the conversion efficiency of the EJ280 WLS. εSA represents the average spectralacceptance of the reflecting surfaces; since the spectral cutoff for the dichroic film is angle-dependent,this acceptance is obtained by averaging the convolution of the WLS emission spectrum with thespectral reflectance of the dichroic film over the range of incidence angles. This value is estimatedvisually to a very rough precision, more accurate calculations can be done by folding all relevantspectral characteristics, but this is only viable if the angular distribution of the incoming photons isknown. εcoll is the efficiency of the reflecting surfaces to deliver photons to the SiPM openings.The value of εcoll can be estimated analytically [19] and is expressed by the surface reflectioncoefficient R490 at a given wavelength (490 nm) and the fraction of surface covered by the SiPMactive area f = Sdet/Stot, where Stot and Sdet are total detector surface area and area covered bySiPMs, respectively:εcoll =f1− < R490 > (1− f )The main components of the final PDE are shown in Table 1. For these calculations the attenuationof green light inside the bulk EJ280 WLS material is neglected, since the attenuation length is of theorder of meters [7]. Unless the source is sited, values and their uncertainties are obtained by estimationfrom the measured spectral curves. Uncertainty of the QPDE is obtained by error propagation.The collection efficiency εcoll scales with the SiPM coverage area f , as shown in Figure 7. The arrowindicates the value of the coverage for the prototype under study. Two curves are shown, one for areflection coefficient of 98%, as used in the studied prototype (see Figure 5 and [15]), and one for apotentially improved setup with 99% (better spectral match of dichroic film to the WLS emission).Figure 7. Collection efficiency as a function of the silicon photomultipliers (SiPM) area coveragefraction f. The 98% reflection coefficient is that used in the prototype [15], 99% shows a potentialimprovement. The arrow indicates the value of the SiPM coverage for the prototype.Instruments 2018, 2, 3 6 of 8Table 1. Summary of parameters and their values used in PDE estimation.Parameter Value Parameter ValueεTPB 1.2 ± 0.1 [6] T425 0.87 ± 0.05εWLS 0.86 [17] εSA 0.7 ± 0.4Sdet 0.36 cm2 Stot 216 cm2εcoll 0.077 εSiPM 0.38 ± 0.02 [18]R490 0.98 ± 0.01 QPDE 0.007 ± 0.0043. MeasurementsMaking a stable source of light pulses containing ∼100 photons is a challenging task. For thispurpose a combination of a 241Am radioactive source and a thin scintillating foil was used. The sourceemits α-particles with mean energy of ≈3 MeV (the active material is embedded inside a Rhodiummatrix). The 0.5 mm thick NE102A (EJ212) scintillating foil (λmax = 423 nm [20]) was brought intocontact with the source surface. The intensity of light pulses were calibrated with a Philips 56AVPvacuum PMT, with a known quantum efficiency of QE = 22 ± 2% at 423 nm.The peak voltage of the PMT output pulse is proportional to number of photoelectrons, Npe, in apulse, assuming pulse shape is constant: V = GNpe. The single photo-electron voltage response, G,was determined with a pulsed LED using the technique described in [21]. The ideal Poisson varianceof the PMT output voltage signal is defined by σ2V = G2Npe. In reality, this value is approximatelyfour times larger for a typical PMT [21], due to contributions from an excess noise factor and severalother effects. Therefore, G was calculated as G = 14σ2V/V for several voltages and the mean taken.The obtained value of G = 3.3 ± 0.3 mV/p.e was validated by single-photo-electron response method,observing signal from very low light pulse intensity (<1 p.e.).Using this PMT, the intensity of the light pulses from the scintillator based light source wasestimated to be at the level of 700 ± 100 photons per pulse. This number was used to derive thePDE of the 10× 10 cm2 prototype detector. The results of this measurement are shown in Figure 8,where the PDE distribution over the 10× 10 cm2 area of the detector is plotted. The measurementswere conducted at room temperature. At 87K, in LAr, a small drift in spectral characteristics of dichroicfilm is expected due to mechanical shrinkage of the reflecting stack structure. However, this shift islimited to about 2% (assuming thermal expansion factor of less than 10−4 K−1). Such a change shouldnot lead to a noticeable variation of the PDE, withing given measurement uncertainty.Figure 8. ArCLight measured photon detection efficiency (PDE) map overlaid onto the 10× 10 cm2surface of the detector. Color scale is shown in % units. Increase in PDE near SiPM side is due toincreased fraction of direct photons, avoiding initial loss at first reflection from the dichroic mirror.Short component of WLS bulk attenuation is likely contributing to this direct access as well.Instruments 2018, 2, 3 7 of 84. ConclusionsA novel design for a large-area photon detector is proposed. The ArCLight device is made ofdielectric materials, except a single edge where SiPMs are mounted. The thin and robust structure withapproaching 100% active area allows efficient integration into large LArTPCs, as well as other liquidscintillator based detectors. The photon detection efficiency for a 10× 10 cm2 detector prototype wasmeasured to be of the order of 1% (in the range of 0.8% to 2.2% ), which has shown good agreementwith theoretical expectations. The design is expected to be easily scalable to several square meters ofsurface area due to long (order of meters) attenuation length of the used WLS plastic. The prototypewas found to be efficient in the wavelength range of 400–460 nm. However, the design could beadjusted for different spectral ranges by a suitable choice of materials.Acknowledgments: The study is supported by grant 200021-169045 of Swiss National Science Foundation and byCanton of Bern, Switzerland.Conflicts of Interest: The authors declare no conflict of interest.References1. Ereditato, A.; Göldi, D.; Janos, S.; Kreslo, I.; Lüthi, M.; von Rohr, C.R.; Schenk, M.; Strauss, T.; Zeller, M.;Weber, M.S. Measurement of the drift field in the ARGONTUBE LAr TPC with 266 nm pulsed laser beams.J. Instrum. 2014, 9, P11010.2. Ereditato, A.; Göldi, D.; Janos, S.; Kreslo, I.; Lüthi, M.; von Rohr, C.R.; Schenk, M.; Strauss, T.; Zeller, M.;Weber, M.S. Performance of cryogenic charge readout electronics with the ARGONTUBE LAr TPC. J. Instrum.2014, 9, P11022.3. Auger, M.; Blatter, A.; Ereditato, A.; Göldi, D.; Janos, S.; Kreslo, I.; Strauss, T. von Rohr, C.; Weber, M.S.On the Electric Breakdown in Liquid Argon at Centimeter Scale. J. Instrum. 2016, 11, P03017.4. Auger, M.; Ereditato, A.; Sinclair, J.R. ArgonCube: AModular Approach for Liquid Argon TPC Neutrino Detectors forNear Detector Environments; SPSC-I-246. Available online: http://cds.cern.ch/record/2268439/files/SPSC-I-246.pdf (accessed on 2 Febuary 2018).5. Acciarri, R.; Acero, M.A.; Adamowski, M.; Adams, C.; Adamson, P.; Adhikari, S.; Anderson, J. Long-BaselineNeutrino Facility (LBNF) and Deep Underground Neutrino Experiment (DUNE). arXiv 2016, arXiv:1601.05471.6. Gehman, V.M.; Seibert, S.R.; Rielage, K.; Hime, A.; Sun, Y.; Mei, D.M.; Moore, D. Fluorescence efficiency andvisible re-emission spectrum of tetraphenyl butadiene films at extreme ultraviolet wavelengths. Nucl. Instrum.Meth. Sec. A 2011, 654, 116–121.7. Howard, B.; Mufson, S.; Whittington, D.; Adams, B.; Baugh, B.; Jordan, J.R.; Pla-Dalmau, A. A novel use oflight guides and wavelength shifting plates for the detection of scintillation photons in large liquid Argondetectors. arXiv 2012, arXiv:1710.11233.8. Moss, Z.; Bugel, L.; Collin, G.; Conrad, J.M.; Jones, B.J.P.; Moon, J.; Wongjirad, T. Improved TPB-coated LightGuides for Liquid Argon TPC Light Detection Systems. J. Instrum. 2015, 10, P08017.9. Ignarra, C.M. A Demonstration of Light Guides for Light Detection in Liquid Argon TPCs. Phys. Procedia2012, 37, 1217–1222.10. Bugel, L.; Conrad, J.M.; Ignarra, C.; Jones, B.J.P.; Katori, T.; Smidt, T.; Tanaka, H.K. Demonstration of alightguide detector for liquid argon TPCs. Nucl. Instrum. Meth. 2011, 640, 69–75.11. Baptista, B.; Bugel, L.; Chiu, C.; Conrad, J.M.; Ignarra, C.M.; Jones, B.J.P.; Mufson, S. BenchmarkingTPB-coated Light Guides for Liquid Argon TPC Light Detection Systems. arXiv 2012, arXiv:1210.3793.12. Jones, B.J.P. A Simulation of Optical Attenuation in TPB Coated Light-guides. J. Instrum. 2013, 8, C10015.13. Whittington, D. Photon detection system designs for the Deep Underground Neutrino Experiment. J. Instrum.2016, 11, C05019.14. Machado, A.A.; Segreto, E. ARAPUCA a new device for liquid argon scintillation light detection. J. Instrum.2016, 11, C02004.15. 3M Optical Systems. Vikuiti Enhanced Specular Reflector (ESR). Available online: http://multimedia.3m.com/mws/media/374730O/vikuiti-tm-esr-sales-literature.pdf?fn=ESR%20ss2.pdf (accessed on 2 Febuary 2018).Instruments 2018, 2, 3 8 of 816. Francini, R.; Montereali, R.M.; Nichelatti, E.; Vincenti, M.A.; Canci, N.; Segreto, E.; Perfetto, F. VUV-Visoptical characterization of Tetraphenyl-butadiene films on glass and specular reflector substrates from roomto liquid Argon temperature J. Instrum. 2013, 8, P09006.17. ELJEN Technology. Wavelength Shifting Plastics EJ-280, EJ-282, EJ-284, EJ-286. Available online: http://www.eljentechnology.com/products/wavelength-shifting-plastics/ej-280-ej-282-ej-284-ej-286 (accessed on2 Febuary 2018).18. Hamamatsu Photonics. S13360 Series: MPPCs for Precision Measurements. Available online: http://www.hamamatsu.com/resources/pdf/ssd/s13360_series_kapd1052e.pdf (accessed on 2 Febuary 2018).19. Segreto, E. An analytic technique for the estimation of the light yield of a scintillation detector. J. Instrum.2012, 7, P05008.20. ELJEN Technology. Wavelength Shifting Plastics EJ-200, EJ-204, EJ-208, EJ-212. Available online: http://www.eljentechnology.com/products/plastic-scintillators/ej-200-ej-204-ej-208-ej-212 (accessed on 2 Febuary 2018).21. Arisaka, K. Absolute Calibration of PMT. Available online: http://home.physics.ucla.edu/~arisaka/Talks/2002/Arisaka_021006_Utah_Absolute_Calibration.pdf (accessed on 2 Febuary 2018).c© 2018 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open accessarticle distributed under the terms and conditions of the Creative Commons Attribution(CC BY) license (http://creativecommons.org/licenses/by/4.0/).

ArgonCube Light readout system (ArCLight) is a novel device for detecting scintillation light over large areas with Photon Detection Efficiency (PDE) of the order of a few percent. Its robust technological design allows for efficient use in large-volume particle detectors, such as Liquid Argon Time Projection Chambers (LArTPCs) or liquid scintillator detectors. Due to its dielectric structure it can be placed inside volumes with high electric field. It could potentially replace vacuum PhotoMultiplier Tubes (PMTs) in applications where high PDE is not required. The photon detection efficiency for a 10 × 10 cm2 detector prototype was measured to be in the range of 0.8% to 2.2% across the active area

Multidisciplinary Digital Publishing Institute

Directory of Open Access Journals

ArCLight - a Compact Dielectric Large-Area Photon Detector

ArCLight - a Compact Dielectric Large-Area Photon Detector

Abstract

Similar works

Full text

Available Versions

Crossref

Bern Open Repository and Information System (BORIS)

Multidisciplinary Digital Publishing Institute

Directory of Open Access Journals