Large Area Photomultipliers Research Articles

Time calibration and synchronization of the scintillation light detection system in ICARUS-T600

The ICARUS-T600 Liquid Argon (LAr) Time Projection Chamber (TPC) is presently taking data in the Short Baseline Neutrino (SBN) program at Fermilab (U.S.A.) to search for a possible LSND-like sterile neutrino signal at Δm 2 ≈ 1 eV2 with the Booster Neutrino Beam (BNB). A light detection system, based on 360 large area Photo-Multiplier Tubes (PMTs), has been realized for ICARUS-T600 to detect VUV photons produced by the passage of ionizing particles in LAr. This system is fundamental for the TPC operation, providing an efficient trigger and contributing to the 3D reconstruction of events. Moreover, since the detector is exposed to a huge flux of cosmic rays due to its shallow depths installation, the light detection system allows for the time reconstruction of events, contributing to the identification and to the selection of genuine neutrino interactions. The correct time reconstruction of events requires the precise knowledge of the delay of each PMT channel and a good synchronization of recording electronics, this last based on fast sampling digitizers. To achieve a time resolution better than 1 ns, we perform three consecutive timing corrections deployed at different stages of the optical data flow. Results demonstrate the capability of the ICARUS-T600 light detection system to allow a precise reconstruction of the temporal evolution of each event occurring in the detector and the association of neutrino events with the bunched structure of BNB.

The laser diode calibration system of the ICARUS T600 detector at FNAL

The ICARUS T600 LAr TPC is the far detector of the Short Baseline Program at FNAL. As it will have to work at shallow depth in the Booster Neutrino Beam, a large cosmic rays background (∼ 11 kHz) will be present. To reduce it, precise timing information is needed from the new light detection system, based on 360 large area photomultipliers. For precise time measurements a calibration system based on a fast laser diode and a system based on one optical switch, several 01 × 1 fused fiber splitters, ultra-high vacuum optical feedthroughs and multimode optical patchcords up to 20 m long, to distribute the laser pulses to each single PMT, was designed. The time evolution of the PMTs' gain/timing and possibly their initial calibrations at a time t0 will be done by using this system. The expected time resolution of this calibration system will be around 100 ps. The laboratory tests needed to set up the system are reported.

Brand-new optical modules for the KM3NeT neutrino detector

Neutrino telescopes in water and ice can be described as a grid of optical sensors, called optical modules, which are sensitive to the Cherenkov radiation emitted by charged particles produced by neutrino interactions.Despite the same scientific objects, all the current projects adopted different optical module designs.IceCube, ANTARES and Baikal-GVD use a single large area photomultiplier, with a photocathode diameter of 10 inch, housed into 13" or 17" diameter transparent glass vessels.The KM3NeT project started a mass production of optical modules with an innovative multi-PMT design that comprises 31 3-inch photomultipliers integrated into a 17" glass sphere. This novel solution has several advantages with respect to the single large area photomultiplier solution: the segmented photocathode layout offers photon counting with higher efficiency and provides directional information and efficient rejection of optical background just at the photosensors detection level, with an almost uniform angular coverage.The paper deals with a general overview on the design of the different optical modules of the current neutrino detectors, with a particular focus on the multi-PMT solution of the KM3NeT project.

Front-end electronic system for large area photomultipliers readout

Abstract We developed a front-end electronic system for large area photomultipliers. Connection to the PMT can be made by a single cable, useful to minimize cabling in a underwater detector. The cabling is done in the rear part of the crate to permit easy access to the electronic boards. A front-end board houses 8 channels each one is composed by a preamplifier and a leading edge discriminator. Up to 8 front-end boards can be housed in a crate, giving a modularity of 64 channels. A controller board is needed to setup and monitor the front-end parameters. This board implements also scalers and time to digital converters with time over threshold capability. A standard gigabit ethernet line is used for communication with the outside world. Details on the design and specification of the system is reported together some preliminary measurements done with the prototypes now under test in laboratory.

Characterization of 750 Large Area Photomultipliers for the KM3NeT-Italia Towers

The KM3NeT European experiment is building a large volume underwater neutrino telescope in the depths of the Mediterranean Sea. Thanks to a dedicated funding by the Italian Ministry of Education, University and Research, named KM3NeT-Italia in its first phase, an eight-tower detector is under construction. It is equipped with 672 optical sensors, called “optical modules,” (OM) which represent the detection elements of the telescope. They are composed by a 13-in high-pressure resistant glass-vessel that contains a single 10-in photomultiplier. As the key sensor, all the characteristics of the photomultiplier have a severe impact on the performance of the whole detector. The selected photomultiplier was the 10-in R7081 photomultiplier tubes (PMTs) produced by Hamamatsu. In the frame of the OM mass production, performed in the INFN site of Catania, 750 photomultipliers have been tested by means of a dedicated test bench. This paper deals with the procedures and the main results of such massive measurements.

Charge reconstruction in large-area photomultipliers

Large-area PhotoMultiplier Tubes (PMT) allow to efficiently instrument Liquid Scintillator (LS) neutrino detectors, where large target masses are pivotal to compensate for neutrinos' extremely elusive nature. Depending on the detector light yield, several scintillation photons stemming from the same neutrino interaction are likely to hit a single PMT in a few tens/hundreds of nanoseconds, resulting in several photoelectrons (PEs) to pile-up at the PMT anode. In such scenario, the signal generated by each PE is entangled to the others, and an accurate PMT charge reconstruction becomes challenging. This manuscript describes an experimental method able to address the PMT charge reconstruction in the case of large PE pile-up, providing an unbiased charge estimator at the permille level up to 15 detected PEs. The method is based on a signal filtering technique (Wiener filter) which suppresses the noise due to both PMT and readout electronics, and on a Fourier-based deconvolution able to minimize the influence of signal distortions—such as an overshoot. The analysis of simulated PMT waveforms shows that the slope of a linear regression modeling the relation between reconstructed and true charge values improves from 0.769 ± 0.001 (without deconvolution) to 0.989 ± 0.001 (with deconvolution), where unitary slope implies perfect reconstruction. A C++ implementation of the charge reconstruction algorithm is available online at [1].

Characterization of SiPM arrays in different series and parallel configurations

A number of innovative experiments dedicated to neutrino and rare-event physics use liquefied noble-gases both as a target and as a detector. These media have the remarkable property to efficiently produce scintillation photons after the passage of ionizing particles. Scintillation light, which is used for triggering and timing purposes, is traditionally detected by large area Photo-Multiplier Tubes (PMTs) working at cryogenic temperature. Silicon Photo-Multiplier (SiPM) arrays are gradually substituting PMTs in many applications, especially where low voltages are required and magnetic field is present. One of the problems of this devices is the small active area. For this reason we built several prototype arrays made by different SiPM models with a common readout: the basic unit is a device with an active area of (1.2×1.2)cm2. A fast signal leading edge is crucial to realize devices to be used for triggering and timing. To this purpose we studied different series/parallel electrical configurations to obtain the best timing performance, by operating our custom arrays both at room and cryogenic temperatures.

Comparison between large area PMTs and SiPM arrays deployed in a Liquid Argon Time Projection Chamber at CERN

Liquid argon Time Projection Chambers (LAr-TPCs) are among the most promising detectors for the study of neutrino oscillations. They are composed by a multi-wire drift chamber to collect the charge and a photodetection system to detect the scintillation light, both produced by ionizing charged particles that cross the argon volume. Scintillation light plays a fundamental role for the event reconstruction because it permits to calculate the absolute time t0 of the event and it is also used for triggering purposes. We present a comparison between the performances of large area Photo-Multiplier Tubes (PMTs) and Silicon Photo-Multiplier (SiPM) arrays deployed in a small LAr-TPC exposed to cosmic rays at CERN, both in terms of light collected and timing performances.

The SuperNEMO calorimeter

The SuperNEMO double beta decay project is a modular tracker-calorimeter experiment that will reach a sensitivity to the neutrinoless double beta decay half-life of ∼ 1026 years, corresponding to a Majorana neutrino mass of 50-100 meV. The main calorimeter is based on 440 Optical Modules made of large volume plastic scintillators (10L) coupled with large area photomultipliers (Hamamatsu R5912-Mod). They are assembled in walls surrounding the isotope foil and the tracking volume. One of the main challenges of the SuperNEMO detector development programme was to reach an energy resolution, better than 8%(FWHM) at 1 MeV. The other challenge was to satisfy the radiopurity requirements for all the calorimeter materials. The calorimeter design of the first SuperNEMO module is presented as well as its performances and the status of its construction under way in the Modane underground laboratory.

Development of an optical simulation for the SuperNEMO calorimeter

The SuperNEMO double beta decay project is a modular tracker-calorimeter based experiment. The aim of this project is to reach a sensitivity of the order of 1026 years concerning the neutrinoless double beta decay half-life, corresponding to a Majorana neutrino mass of 50-100 meV. The main calorimeter of the SuperNEMO demonstrator is based on 520 Optical Modules made of large volume plastic scintillators (10L) coupled with large area photomultipliers (Hamamatsu R5912-MOD and R6594). The design of the calorimeter is optimized for the double beta decay detection and allows gamma tagging for background rejection. In large volumes of scintillators, a similar deposited energy by electrons or photons will give different visible energy and signal shapes due to different interactions inside the scintillator. The aim of the optical simulation, developed for SuperNEMO, is to model the Optical Module response on the energy and time performances, regarding the particle type.

Status of the 20 inch MCP-PMT prototype development for JUNO experiment

A new concept of large area photomultiplier based on MCPs was conceived for JUNO by the scientists in IHEP, Beijing. In the past 5 years by collaborative work of the MCP-PMT collaboration in China, 8 inch and 20 inch prototypes were produced. Test results show that this type of MCP-PMT can have similar photon counting performance as the traditional dynode type PMTs. With the better collection efficiency, low after pulse rate, low Low-Potassium Glass, the JUNO ordered 75% about 15,000 20 inch MCP-PMT from NNVT at the end of 2015. This manuscript just give the overview this type of MCP-PMT, the R&D process and the main characteristics.

A Study on 3-in- and 10-in-Diameter Photomultiplier Tubes for the KM3NeT Project

Photomultiplier tubes (PMTs) are widely used in neutrino and astroparticle detectors, inserted into transparent pressure-resistant glass vessels called optical modules (OMs). They compose of an array of photo sensors located in the underwater or under the ice environment to measure the Cherenkov light emitted by charged particles produced by neutrino interactions. Currently, there are two main designs for the OMs used in the operating neutrino telescopes: a design with a single large photomultiplier, typically with a photocathode diameter of 10 in, contained in a pressure resistant glass vessel of 17-in or 13-in diameter, and an innovative design of a pressure-resistant 17-in-diameter glass vessels that hosts 31 PMTs of 3-in photocathode diameter. The KM3NeT collaboration is building a cubic-kilometer-sized neutrino telescope in the depths of the Mediterranean Sea, and OMs of both types are produced to compose a string-like underwater detection units, which use small-area PMTs, and tower-like detection units, which use the single large area photomultiplier design. The main characteristics of two batches of 3-in and 10-in photomultipliers were investigated and the main results are reported in this paper.

Evaluation of new large area PMT with high quantum efficiency*Supported by Strategic Priority Research Program of Chinese Academy of Sciences (X-DA10010200), Key Deployment Project of Chinese Academy of Sciences and CAS Center for Excellence in Particle Physics (CCEPP)

The neutrino detector of the Jiangmen Underground Neutrino Observatory (JUNO) is designed to use 20 kilotons of liquid scintillator and approximately 16 000 20 inch photomultipliers (PMTs). One of the options is to use the 20 inch R12860 PMT with high quantum efficiency which has recently been developed by Hamamatsu Photonics. The performance of the newly developed PMT preproduction samples is evaluated. The results show that its quantum efficiency is 30% at 400 nm. Its Peak/Valley (P/V) ratio for the single photoelectron is 4.75 and the dark count rate is 27 kHz at the threshold of 3 mV while the gain is at 1 × 107. The transit time spread of a single photoelectron is 2.86 ns. Generally the performances of this new 20 inch PMT are improved over the old one of R3600.

The R&D of the 20 in. MCP–PMTs for JUNO

A new concept of large area photomultiplier based on MCPs was conceived for JUNO by the scientists in IHEP, and with the collaborative work of the MCP–PMT collaboration in China, 8in. and 20in. prototypes were produced. Test results show that this type of MCP–PMT can have good SPE performance as the traditional dynode type PMTs.

A study on large area Hamamatsu photomultipliers for Cherenkov neutrino detectors

Many of the existing neutrino telescopes use large area photomultipliers integrated into transparent glass vessels to make the detection element called ``optical module''. The characteristics of the photomultipliers have a severe impact on the performance of the whole detectors. This paper describes a large work of characterization of large area photomultipliers performed in the frame of R&D activities of large volume underwater neutrino detectors. Dedicated studies are also reported about noise pulses, super bialkali photocathode photomultipliers, ageing effects, influences of the Earth's magnetic field and on the effects of the external glass vessels on the optical module's noise pulses.

Application of three-photon excitation FCS to the study of protein oligomerization.

Three-photon excitation fluorescence correlation spectroscopy was used to detect oligomerization equilibria of rat liver phosphofructokinase. The fluorescence intensity produced by the three-photon excitation of tryptophan was collected using the DIVER microscope. In this home-built upright microscope, a large area photomultiplier, placed directly below the sample, is used as the detector. The lack of optical elements in the microscope detection path results in a significantly improved detection efficiency in the UV region down to about 300 nm, which encompasses the fluorescence emission from tryptophan. The three-photon excitation autocorrelation decays obtained for phosphofructokinase in the presence of F6P showed the presence of large oligomers. Substitution of F6P with ATP in the buffer medium results in dissociation of the large oligomers, which is reported by the decreased autocorrelation amplitude. The three-photon excitation process was verified from the slope of the log–log plot of intensity against laser power.

Noise Pulses in Large Area Optical Modules

Large area photomultipliers are widely used in neutrino and astro-particle detectors to measure Cherenkov light in media like water or ice. The key element of these detectors are the so-called ”optical module”, which consists of a photodetector enclosed in a transparent pressure-resistant container to protect it and ensure good light transmission. Noise pulses at the anode of each photomultiplier strongly affect the performance of the detector. A large study was conducted on noise pulses of large area photomultipliers, considering time and charge distributions of dark pulses, pre-pulses, delayed pulses, and after pulses. The contribution to noise pulses due to the presence of the external glass vessels was also studied, even comparing two vessels of different brands.

Characterization of large area photomultiplier ETL 9357FLB for liquid argon detector

The China Dark Matter Experiment (CDEX) Collaboration will carry out a direct search for weakly interacting massive particles with germanium detectors. Liquid argon will be utilized as an anti-Compton and cooling material for the germanium detectors. A low-background and large-area photomultiplier tube (PMT) immersed in liquid argon will be used to read out the light signal from the argon. In this paper we have carried out a careful evaluation on the performance of the PMT operating at both room and cryogenic temperatures. Based on the single photoelectron response model, the absolute gain and resolution of the PMT were measured. This has laid a foundation for PMT selection, calibration and signal analysis in the forthcoming CDEX experiments.

Aging characterization on large area photo-multipliers

An accurate study and measurement about the aging effects on two large area photomultipliers (PMT) has been performed for over 3 years. The PMTs were 10in., 10 stages Hamamatsu R7081, one with standard bialkali and the other one with super-bialkali photocathode. The gain, dark count rate, charge and timing properties have been measured, as well as the fraction of the spurious pulses. During the aging cycles, the anode current of the two photo-multipliers has been monitored and recorded in order to measure the total output anode charge and determine the aging grade. The aging conditions have been set by the use of a 400nm LED regulated to about 3 photoelectrons (pe) at about 400kHz. The aging process was stopped when the total charge arrived up to about 2000C for both the PMTs. Measurements of the parameters of the two PMTs have been performed periodically using a 400nm pulsed laser in single photoelectron condition. Considering the main results, only the gain showed a variation while all the other parameters remain quite stable. A first phase of up-drift shows an increase of the gain of about 10% and is followed by a final phase of down drift, which shows a faster diminution of the gain of about 30%. The mechanism of the gain drift has been modeled and compared with the results.

Influence of the Earth's Magnetic Field on Large Area Photomultipliers

The influence of the Earth's magnetic field on large area photomultipliers proposed for a future deep sea neutrino telescope was studied under the EU-funded KM3NeT design study. The aims were to evaluate variations in PMT performance in the Earth's magnetic field and to decide whether the use of magnetic shielding is necessary. Measurements were performed on three Hamamatsu PMTs: two 8-inch R5912 types, one of these with super bialkali photocathode, and a 10-inch R7081 type with a standard bialkali photocathode. The various characteristics of the PMTs were measured while varying the PMT orientations with respect to the Earth's magnetic field, both with and without a mu-metal cage as magnetic shield. In the 8-inch PMTs the impact of the magnetic field was found to be smaller than that on the 10-inch PMT. The increased quantum efficiency in the 8 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{\prime\prime}$</tex> </formula> super bialkali PMT almost compensated its smaller detection surface compared to the 10 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{\prime\prime}$</tex> </formula> PMT. No significant effects were measured upon transit time and the fraction of spurious pulses.