Transit Time Spread Research Articles

Proton and muon beam tests for ultra-fast MCP-PMT detectors

In collaboration with the North Night Vision Science and Technology (Nanjing) Research Institute Co. Ltd, researchers at the Institute of High Energy of Physics in China have successfully developed the 20-inch micro-channel-plate photomultiplier tube (MCP-PMT) that exhibits high detection efficiency (DE) for use in the Jiangmen Underground Neutrino Observatory (JUNO). Due to the long drift path of electrons from photocathode to MCP, the 20-inch MCP-PMT has a time resolution on the order of nanoseconds. Recently, the team has made advancements in ultra-fast MCP-PMTs (FPMTs), achieving picosecond-level time resolution with both 1-inch and 2-inch types. By now, prototypes featuring single-anode, 2 × 2 anodes, 4 × 4 anodes, and 8 × 8 anodes have been successfully manufactured and tested. The 8 × 8 anode FPMT, in particular, demonstrates a transit time spread (TTS) of 36 ps (Sigma) in single photon mode, thanks to its meticulously engineered structure. To assess the FPMT’s time performance under beam conditions, two beam tests were conducted at Fermi Lab and CERN. In these tests, the 8 × 8 pixel arrays of four distinct radiators, including LYSO, BGO, Pb glass and quartz glass, were paired with the 8 × 8 anodes FPMT. This setup involved the use of two radiator-coupled FPMT detectors for particle detection. The best coincidence time resolution recorded was 64 ps (Sigma) with a 120 GeV proton beam and 56 ps (Sigma) with a 108 GeV muon beam.

Simulation of electron transport in a catoptric photomultiplier tube concept for large rectangular scintillator crystals

Spectroscopic scintillation detector form factors have been guided primarily by the design of commercially available photonic sensors. These devices, such as photomultiplier tubes, silicon photomultipliers, and hybrid photodetectors have underperformed in one or more areas such as size, power consumption, and resolution. A novel photomultiplier tube having a 50.8×152.4 mm2 rectangular window, utilizing a reflection-mode photocathode, and a low-gain, miniaturized dynode set is considered here to improve photosensor packaging while enabling high-efficiency, low-resolution scintillation spectroscopy with large, planar scintillators. Using a phenomenological multiphysics simulation process informed by empirical data, photoelectron collection efficiency, single-photoelectron response, electron transit time, and transit time spread have been modeled over a range of operating potentials. At 750 V between the photocathode and anode, 72.5% of photoelectrons are collected at the first dynode, and the average gain is estimated to be 805. The most probable transit time is 14.9 ns, with a transit time spread of 2.7 ns full-width at half-maximum.

Characterization of the Hamamatsu 8-inch R14688-100 PMT

Large-scale optical neutrino and dark-matter detectors rely on large-area photomultiplier tubes (PMTs) for cost-effective light detection. The new R14688-100 8-inch PMT developed by Hamamatsu provides state-of-the-art timing resolution of around 1 ns (FWHM), which can help improve vertex reconstruction and enable Cherenkov and scintillation light separation in scintillation-based detectors. This PMT also provides excellent charge resolution, allowing for precision photoelectron counting and improved energy reconstruction. The Eos experiment is the first large-scale optical detector to utilize these PMTs. In this manuscript we present a characterization of the R14688-100 single photoelectron response, such as the transit-time spreads, the dark-rates, and the afterpulsing. The single photoelectron response measurements are performed for the 206 PMTs that will be used in Eos.

Pushing the limit of BGO-based dual-ended Cherenkov PET detectors through photon transit time correction

Objective. The high production cost of commonly used lutetium-based fast scintillators and the development of silicon photomultipliers technology have made bismuth germanate (BGO) a promising candidate for time-of-flight positron emission tomography (TOF PET) detectors owing to its generation of prompt Cherenkov photons. However, using BGO as a hybrid scintillator is disadvantageous owing to its low photon statistics and distribution that does not conform well to a single Gaussian. To mitigate this, a proposal was made to increase the likelihood of detecting the first Cherenkov photons by positioning two photosensors in opposition at the entrance and exit faces of the scintillator and subsequently selectively picking an earlier timestamp. Nonetheless, the timing variation arising from the photon transit time remains affected by the entire length of the crystal, thereby presenting a possibility for further enhancement. Approach. In this study, we aimed to improve the timing performance of the dual-ended BGO Cherenkov TOF PET detector by capitalizing on the synergistic advantages of applying depth-of-interaction (DOI) information and crystal surface finishes or reflector properties. A dual-ended BGO detector was implemented using a 3 × 3 × 15 mm3 BGO crystal. Coincidence events were acquired against a 3 × 3 × 3 mm3 LYSO:Ce:Mg reference detector. The timing performance of the dual-ended BGO detectors was analyzed using conventionally proposed timestamp methods before and after DOI correction. Results. Through a DOI-based correction of photon transit time spread, we demonstrated a further improvement in the timing resolution of the BGO-based Cherenkov TOF PET detector utilizing a dual-ended detector configuration and adaptive arrival time pickoff. We achieved further improvements in timing resolution by correcting the offset spread induced by the fluctuation of timing signal rise time in the dual-ended detector. Significance. Although polishing the crystal surface was still favorable in terms of full-width-half-maximum value, incorporating DOI information from the unpolished crystal to compensate for photon travel time facilitated additional enhancement in the overall timing performance, thereby surpassing that achieved with the polished crystal.

A new large area MCP-PMT for high energy detection

20-inch Large area photomultiplier tube based on microchannel plate (MCP-PMT) is newly developed in China. It is widely used in high energy detection experiments such as Jiangmen Underground Neutrino Observatory (JUNO), China JinPing underground Laboratory (CJPL) and Large High Altitude Air Shower Observatory (LHAASO). To overcome the poor time performance of the existing MCP-PMT, a new design of large area MCP-PMT is proposed in this paper. Three-dimensional models are developed in CST Studio Suite to validate its feasibility. Effects of the size and bias voltage of the focusing electrodes and MCP configuration on the collection efficiency (CE) and time performance are studied in detail using the finite integral technique and Monte Carlo method. Based on the simulation results, the optimized operating and geometry parameters are chosen. Results show that the mean ratio of photoelectrons landing on the MCP active area is 97.5%. The acceptance fraction of the impinging photoelectrons is close to 100% due to the emission of multiple secondary electrons when hitting the MCP top surface. The mean transit time spread (TTS) of the photoelectrons from the photocathode is 1.48 ns.

A novel fast-timing readout chain for LHCb RICH LS3 and prototype beam tests

The prompt Cherenkov radiation and focusing optics of the LHCb RICH detectors allow the prediction of the Cherenkov photon detection time from a given charged particle to within 10ps. Fast-timing information on the detected Cherenkov photons can therefore be used to significantly improve the particle identification (PID) performance and the signal-to-background ratio of the detectors. This concept is a cornerstone for the LHCb RICH detector upgrades and will ultimately allow the system to operate at a luminosity in excess of 1034cm−2s−1 during HL-LHC Run 5. A new electronic readout chain is proposed for the LHC Long Shutdown 3 (LS3, 2026-2028) using the FastRICH, a novel ASIC under development. The specifications for the FastRICH are discussed in the context of the LS3 enhancements and LHCb Upgrade II. The FastRICH will perform multi-channel single-photon discrimination, timestamp photons with 25 ps bin size, integrate closely with the LHCb optical link chipset and apply data-compression techniques. The detector will be capable of timestamping each photon with 150ps resolution dominated by the existing Multianode Photomultiplier Tube (MAPMT) transit-time spread. The new electronic readout chain introduces important timing and detector techniques ahead of the Upgrade II RICH system overhaul and the FastRICH has the flexibility to be coupled to sensors with better time resolution for HL-LHC Run 5. Simulation studies have demonstrated improvements in the hadronic PID performance during Run 4 using the FastRICH coupled to MAPMTs. A first version of the readout chain, based on the FastIC, a predecessor of the FastRICH, and a TDC-in-FPGA, has been studied using Cherenkov photons at the CERN SPS charged particle beam test facility.

A novel multi-anode MCP-PMT with Cherenkov radiator window

With the proposal of the road map of Time-of-Flight positron emission tomography (TOF-PET) with a Coincidence Time Resolution (CTR) of 10 ps by Paul Lecoq et al. in 2020, the technology based on TOF puts forward higher requirements on the performance of its core optical devices. In this manuscript, we developed a kind of Multi-Anode micro channel plate photomultiplier tube (MCP-PMT) based on Cherenkov radiator window. By using the Cherenkov radiator as the optical window of Multi-Anode MCP-PMT directly, the optical interface between the scintillator and the PMT window in conventional TOF-PET is eliminated, reducing light loss and further improve the time resolution of TOF-PET. The anode of this MCP-PMT can be split into a finely spaced array of collecting electrodes to achieve good positional sensitivity. In this paper, the single photon detection capability and time resolution of this kind of MCP-PMT are evaluated. The transit time spread (TTS) at single photon mode can reach 42.9 ps, and the TTS at multi photon mode is less than 10 ps. The CTR based on this kind of MCP-PMT is 156.7 ± 10.6 ps FWHM, which is equivalent to a position resolution of 23.5 ± 1.6 mm along a line of response (LOR). The performance uniformity of this kind MCP-PMT has also been calibrated.

LYSO scintillation light test with an ultra-fast MCP-PMT

The scintillator can be seen as a wavelength shifter which converts the incident particle into a number of photons at certain wavelength. The scintillation light decay time of scintillator is measured by coupling the scintillator with the photosensitive device. With the photoelectric conversion process and waveform sampling technology, the waveform of the signal responding to the scintillation light is obtained. Through exponential fitting, we can obtain the decay time of the scintillator. Traditionally the photosensitive device used to measure the scintillation light have a rise time on the order of nanoseconds. In our experiment, an ultra-fast MCP-PMT with a rise time of 100 ps and a transit time spread of 46 ps at single-photon mode was used to be coupled with the Lu1.8Y2SiO5:Ce (LYSO) scintillator and obtain the scintillation light waveforms. The waveform obtained is not a complete scintillation pulse and the photons in one scintillation event are distinguished and becomes discrete pulses. A new method is introduced to measure the decay time of the scintillator and the result for LYSO with the new method is compared to the results measured with the dynode PMT XP2020.

Single photon counting performance of the Auratek-Square MCP-PMT

This paper reports on the time resolution of the Auratek-Square MCP-PMT, a multi-anode microchannel plate photomultiplier produced by Photek.When operating as single photon counter at low photon rate and with a single pixel illuminated it shows a transit time spread (jitter) of ∼100 ps FWHM, saturating at high rate, above ∼100 kHz/mm2.The worsening of the timing performance depends on the bias voltage between the photocathode and the MCP input and between the MCP slabs.The charge sharing between neighbouring pixels can become a major crosstalk source if not accounted for, degrading the time resolution to ∼170 ps FWHM when the entire pixel area is illuminated.

A Large Area Dynode-MCP-PMT Design With High CE and Good Time Performance

A 20-in. photomultiplier tube based on dynode and microchannel plates (Dynode-MCP-PMT) with high collection efficiency (CE) and good time performance is proposed in this article. To obtain a tailless time distribution, a pair of uncoated MCPs are employed. For a high CE, a dynode with two large openings is placed in front of the MCPs. The dynode is designed as a spherical shape to prevent secondaries from escaping the multiplication system and assist them moving to the MCPs for further multiplication. A 3-D model is developed by CST Studio Suite to validate its feasibility. Finite integral technique and Monte Carlo method are combined to simulate the photoelectron collection and multiplication processes. Results predict that for the shielded Dynode-MCP-PMT, CE is expected to be 100%. Tailless transit time distributions are observed. Transit time spread (TTS) of the photoelectrons from the cathode top point to the dynode achieves 3.7 ns. If this PMT is exposed to the geomagnetic field, it should be operated in the north and south direction, in which CE and TTS are expected to be 100% and 3.8 ns, respectively.

R & D of a novel single anode fast timing MCP-PMT

Small-sized Micro-Channel-Plate Photomultiplier Tube (MCP-PMT) has attracted extensive attention in the fields of high-energy physics, medical imaging and biological detection due to its high timing resolution. We report the R&D of a novel single anode MCP-PMT with ultrafast rise time (RT) and transit time spread (TTS), which is called fast-timing PMT (FPMT). In this paper, we mainly optimize the time performance of FPMT by simulation and experiments in three parts, including the gap distance between the MCP and anode, anode structure and high voltage distribution on the electrodes. The results show that by optimizing the anode structure of FPMT, the RT of single-anode FPMT is significantly improved from 1.4 ns to 215 ps and the TTS from 71 ps to 35.8 ps. By optimizing the high voltage distribution of the FPMT, the RT and the TTS are further improved, and the trend of the change in relative time performance with the change in high voltage distribution is analyzed. Finally, a single-anode FPMT with a RT of 153 ps and a TTS of 27.2 ps is realized.

Optimization design of the large area Dynode-MCP-PMT

The optimization work of a newly proposed 20-in. photomultiplier tube based on dynode and microchannel plates (Dynode-MCP-PMT) are conducted in this paper. Three-dimensional models are developed in CST STUDIO SUITE to systematically investigate the effects of the size and bias voltage of the two focusing electrodes, dynode and the glass envelop handle based on the Finite Integral Technique and Monte Carlo method. Results predict that the collection efficiency and the transit time spread of the optimized design are substantially improved which are 100% and 3.7 ns.

Study on the transit time spread characteristic of 20-in. hybrid photomultiplier tube used for high-energy particle detection

According to the requirements of high-energy particle detection for a large photocathode detection surface, low transit time spread (TTS), and low-cost photomultiplier tube (PMT), a kind of 20-in. hybrid large-area PMT based on the silicon (Si) electron multiplier array was designed and optimized. This study tracked the trajectories of photoelectrons from the photocathode to the silicon electron multiplier array based on the Monte Carlo and finite-integral method. The critical effects on the TTS characteristic of the large-area PMT, including the focusing electrode structure, glass shell structure, different potential differences, and relative distance from the photocathode vertex to the silicon electron multiplier array, were studied in detail. After optimizing the structure of the glass shell, the 20-in. hybrid PMT based on the ultra-small Si electron multiplier array with 40 mm collection diameter can achieve an excellent TTS of about 1.87 ns from the photocathode to the Si electron multiplier array at a collection potential difference of 2000 V.

R&D of ultra-fast 8 × 8 anodes MCP-PMT

Cooperating with the North Night Vision Science & Technology (Nanjing) Research Institute Co. Ltd, Institute of High Energy of Physics in China is developing a 2-inch square shape 8 × 8 anodes micro-channel-plate photomultiplier tube (MCP-PMT) with a time resolution of picosecond level. It has a 40 × 40 mm2 bi-alkali photocathode with a peak quantum efficiency (QE) of about 22% around a wavelength of 410 nm. With the chevron MCP stack, the MCP-PMT can reach a gain of over 106 under a working voltage of 1500 V. The typical output waveform has an amplitude of 64 mV and a rise time of 334 ps. Due to the well-designed structure of the MCP-PMT, the transit time spread (TTS) for the middle anode can reach 36 ps when working at single photon mode. To evaluate the performance uniformity of the 8× 8 anodes MCP-PMT, ten anodes which constitutes the smallest repetition unit of the anode array are chosen and tested. The average transit time spread (TTS) for the 64 anodes is 44.1 ± 2.0 ps.

The Wavelength-Shifting Optical Module.

The Wavelength-shifting Optical Module (WOM) is a novel photosensor concept for the instrumentation of large detector volumes with single-photon sensitivity. The key objective is to improve the signal-to-noise ratio, which is achieved by decoupling the photosensitive area of a sensor from the cathode area of its photomultiplier tube (PMT). The WOM consists of a transparent tube with two PMTs attached to its ends. The tube is coated with wavelength-shifting paint that absorbs ultraviolet photons with nearly 100% efficiency. Depending on the environment, e.g., air (ice), up to 73% (41%) of the subsequently emitted optical photons can be captured by total internal reflection and propagate towards the PMTs, where they are recorded. The optical properties of the paint, the geometry of the tube, and the coupling of the tube to the PMTs have been optimized for maximal sensitivity based on theoretical derivations and experimental evaluations. Prototypes were built to demonstrate the technique and to develop a reproducible construction process. Important measurable characteristics of the WOM are the wavelength-dependent effective area, the transit time spread of detected photons, and the signal-to-noise ratio. The WOM outperforms bare PMTs, especially with respect to the low signal-to-noise ratio with an increase of a factor up to 8.9 in air (5.2 in ice). Since the gain in sensitivity is mostly in the UV regime, the WOM is an ideal sensor for Cherenkov and scintillation detectors.

Performance test and qualification of the photomultiplier tube for the whole production of LHAASO-ED

Over 5000 1.5-inch photomultiplier tubes (PMTs) are deployed in the electromagnetic particle detectors (EDs) of the Large High Altitude Air Shower Observatory (LHAASO). The PMTs are developed as two outputs devices (the anode and the 6th dynode) to measure the large dynamic ranges of particle densities within the extensive air shower. Before assembly, the PMTs must be fully tested to ensure the products meet the performance requirements. A dedicated test bench has been designed for this purpose, capable of testing multiple PMTs simultaneously. The major performances such as single photoelectron spectrum, gain versus high voltage, pulse linearity, dark noise rate and temperature coefficient are measured for each PMT, and transit time spread (TTS) is measured from a 5% sample. The PMTs that comply with the requirements are used in the EDs construction. The design of the PMT voltage divider and the test results of 5366 PMTs are presented in this paper.

20-inch photomultiplier tube timing study for JUNO

Jiangmen Underground Neutrino Observatory (JUNO) is a large liquid scintillator neutrino detector now under construction at Jiangmen, Guangdong, China for determination of neutrino mass ordering with 3% energy resolution at 1 MeV, a precise measurement of neutrino oscillation parameters, and other neutrino physics. The central detector is made up of a 35.4-meter diameter acrylic sphere which contains 20 kton of liquid scintillator and is surrounded by about 18k 20-inch photomultiplier tubes (PMTs). The PMTs performance is one of the JUNO’s key successes to reach the high resolution goal. In this study, the PMT characteristic and its timing related responses were determined via the PMT generated signals, extracted from the PMT in a scanning station system. About 2,400 of micro-channel plate PMTs (MCP-PMTs) and dynode PMTs were analyzed for their responses with LED source such as rise time, fall time, transit time spread (TTS), gain, etc., which relate to photon incident on different positions of PMT’s glass surface. Furthermore, we also observed the fluctuation of PMT performance under magnetic field which can decrease the PMT photon detection efficiency (PDE).

Numerical study and improvement of the dynamic performance of dilation x-ray imager.

We present in this Note a numerical study on the dynamic performance of a Dilation X-ray Imager (DIXI). The DIXI including a photoelectron tube (PT) and a magnetic solenoid is modeled in 3D space. The initial parameters of the photoelectrons are sampled with a Monte Carlo code. The trajectories of the photoelectrons are calculated by using the particle-in-cell method, and the transit time spread (TTS) and temporal magnification are analyzed in detail. We have designed a PT with a double-microstrip structure and compared the performance of the double-microstrip PT with the traditional single-microstrip PT. The results show that the sensitivity of the TTS and the temporal magnification to the emission time of the photoelectrons can be significantly reduced by using the double-microstrip PT, resulting in an improvement of the time window. Therefore, the dynamic performance of the DIXI is improved.

Summary of the R&D of 20-inch MCP-PMTs for neutrino detection

The Jiangmen Underground Neutrino Observatory (JUNO) in China aiming to determine the neutrino mass hierarchy is under construction. A new kind of large area microchannel-plate photomultiplier tube (MCP-PMT) was put forward for the JUNO by the researchers in Institute of High Energy Physics (IHEP) in China. After breaking through several core technotical barriers, the 20-inch MCP-PMT prototype with great performance was successfully produced by the MCP-PMT group in China and got 75% PMT orders (15,000 pics) from JUNO. The mass production line and batch test system was completed in North Night Vision Technology Co., Ltd. (NNVT). The performance of the MCP-PMT including the gain, the quantum efficiency, the P/V ratio, the dark count rate and the transit time spread can be batch tested. During the mass production process, the technical progress in the cathode deposition method improved the quantum efficiency of the photocathode from 30% to 35%. The aging behaviour, temperature effect, the after-pulse distribution and the flash signal of the 20-inch MCP-PMT are all detailly studied. By August of 2020, the 15,000 MCP-PMTs, which will be installed as the central liquid scintillator detector of JUNO, have been completed and delivered to Jiangmen. The average QE at 400 nm for the 15,000 pieces of MCP-PMTs is 32%.

Homogeneity of the photocathode in the Hamamatsu R15458-02 Photomultiplier Tube

It is common practice to test the optical properties of photomultiplier tubes (PMTs) by illuminating the entire photocathode region from the front at once and measuring the average performance. However, for optimal utilisation of the PMT performance in experiments, especially in the single-photon region, it is essential to also know the systematic variations across the photocathode, which requires measurements with focused light sources that illuminate only small regions of the PMT. We present a detailed uniformity characterisation of the gain, transit time, transit time spread, and pulse shape of the 80 mm Hamamatsu R15458-02 PMT. We find that the parameters exhibit asymmetry along one axis, likely caused by the position and geometry of the dynode system. For all parameters except the transit time, the observed variations are small given the intrinsic variation of the parameters. For positions with shifted transit time we observe on average underamplified pulses which can potentially be exploited to improve the pulse reconstruction.