- Email: [email protected]
New large aperture, hybrid photo-detector and photo multiplier tube for a gigantic water Cherenkov ring imaging detector
Nuclear Instruments and Methods in Physics Research A 766 (2014) 152–155
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
New large aperture, hybrid photo-detector and photo multiplier tube for a gigantic water Cherenkov ring imaging detector Seiko Hirota a,n , Yasuhiro Nishimura b, Yusuke Suda c, Yuji Okajima d, Masato Shiozawa b, Shoei Nakayama b, Hidekazu Tanaka b, Yoshinari Hayato b, Motoyasu Ikeda b, Masayuki Nakahata b, Masashi Yokoyama c, Hiroaki Aihara c, Atsuko Ichikawa a, Akihiro Minamino a, Kunxian Huang a, Tsuyoshi Nakaya a, Yoshihiko Kawai e, Masatoshi Suzuki e, Takayuki Ohmura e a
Kyoto University, Department of Physics, Japan University of Tokyo, ICRR, Japan c University of Tokyo, Department of Physics, Japan d Tokyo Institute of Technology, Department of Physics, Japan e Hamamatsu Photonics K.K., Japan b
For the Hyper-Kamiokande working group art ic l e i nf o
a b s t r a c t
Available online 11 June 2014
We are developing a 20-in. aperture high quantum efficiency photo-multiplier tube (PMT) and a hybrid photo-detector (HPD) for Hyper-Kamiokande which is a next generation underground large water Cherenkov detector. We have measured prototypes of 20-in. PMT with a high quantum efficiency photocathode, 30% at 400 nm, and 8-in. HPDs with a normal quantum efficiency photocathode, 22% at 400 nm, in a 200-ton water tank and checked their performance. The PMTs have a 2.7 ns (sigma) timing resolution and 43% (sigma) charge resolution for single photo-electron. Compared to PMTs, HPDs show a better performance with a 1.7 ns timing resolution and 32. & 2014 The Authors. Published by Elsevier B.V. All rights reserved.
Keywords: Cherenkov ring imaging detector Hybrid photo-detector High quantum efficiency Hyper-Kamiokande Neutrino
1. Hyper-Kamiokande and requirements for photo-sensors
2. Photo-sensor development for HK
Hyper-Kamiokande (HK) is a next generation gigantic underground Cherenkov ring imaging detector designed to study a wide range of topics in physics and astrophysics related to neutrinos and proton decay [1]. It is a successor detector to Super-Kamiokande (SK) and consists of more than 100,000 photo-sensors and two cylindrical water tanks with one million tonnes mass in total. The requirements of photo-sensors for HK are a large aperture, a few nanoseconds timing resolution, single photon sensitivity and a few kHz dark rate. The timing resolution should be a few nanoseconds to realize a few tens of centimeters vertex resolution of HK in event reconstruction. The single photon sensitivity is required to observe neutrinos in the low energy region around several MeV, such as solar neutrinos and supernova neutrinos. Also the dark rate should be less than several kHz to suppress noise in low energy events.
Candidate photo-sensors for HK manufactured by Hamamatsu Photonics K.K. (HPK) are shown in Fig. 1 and their expected performance is listed in Table 1. In the baseline design of HK, the photo-sensors are the R3600 PMT which has been successfully used for over ten years in SK. The SK PMT has a venetian blind dynode which is used for a large aperture PMTs because a large dynode of this type can be made easily. This is based on an established technology but cost of photo-sensors with this design is high and would contribute onethird of total cost. For the reduction of cost, photo-coverage of HK is designed to be 20% which is half of SK. We are developing another type of PMT and hybrid photodetectors (HPDs) to pursue possibility of lower cost and higher performance than the first candidate. We also aim to make quantum efficiency higher for all candidates in order to try an additional cost saving by reducing the number of photo-sensors while maintaining the photo-detection efficiency.
n
Corresponding author. E-mail address: [email protected] (S. Hirota).
http://dx.doi.org/10.1016/j.nima.2014.06.010 0168-9002/& 2014 The Authors. Published by Elsevier B.V. All rights reserved.
S. Hirota et al. / Nuclear Instruments and Methods in Physics Research A 766 (2014) 152–155
153
Fig. 1. Hyper-Kamiokande photo-sensor candidates.
Table 1 Estimated performance of 20-in. photo-sensor candidates for HK.
Amplification QE CE 1 p.e.b separation (Peak to Valley ratio) Timing resolution (FWHM) Gain HV a b c
SK PMT (R3600 HPK)
B&L PMT (R12860 HPK)
HPD (R12850 HPK)
Venetian blind dynode 22%a 80% 1.4 5.5 ns 106–107 2 kV
Box and line dynode 30% 93% 2:5 2.7 ns 106–107 2 kV
Avalanche diode 30% 95% 3 0.75 ns 104–105 8 kVc
HQE R3600 can achieve 30% quantum efficiency. Photo-electron. The electric potential around the AD is 8 kV and the bias voltage of the AD is about 300 V.
2.1. Box-and-line PMT A new PMT design with a box and line (B&L) dynode has been developed to improve timing resolution and collection efficiency compared to SK PMT with the venetian blind type. 2.2. HPD An HPD is a hybridization of a photo tube and an avalanche diode (AD). Due to the smaller gain than PMTs, HPDs need preamplifiers. However, the HPD has a better single photon charge resolution than that of PMTs because the initial amplification of an HPD is larger than those of PMTs [2]. The timing resolution and collection efficiency are also better than that of PMTs due to higher voltage of 8 kV. Moreover using AD instead of dynode may lead to the reduction of cost because the dynode is significant fraction of the cost of a PMT.
3. Test in a 200-ton water tank We have been testing new photo-sensors in a 200-ton water tank from autumn 2013. Our goal is to confirm stable operation of new photo-sensors over a few years in the water tank because they have not previously been used in a water. The stability of performance such as single photon resolution in charge, timing resolution and dark rate are monitored. Of particular interest is how much the dark rate of a high quantum efficiency (HQE) PMT reduces in the water tank because thermal electrons from the photo-cathode are the main source of dark rate above single photo-electron level.
Fig. 2. Quantum Efficiency of HQE R3600 PMT samples for the first proof-test.
PMT. We will equip other candidates with HQE photocathode based on this study. Eight HQE R3600 PMTs were produced and have the peak quantum efficiency about 30% (Fig. 2). Also a normal quantum efficiency (NQE) HPD prototype has been developed for the test with an 8-in. diameter size which is the same size as photo-sensors to be used in the veto layer of HK. The 8-in. prototype HPD modules are equipped with pre-amplifiers and a high voltage power supply on the back side, covered by a water-proof housing. The HV power supply is operated by a low voltage of 5 V to avoid exposure of 8 kV line in water. The better performance such as single photo-electron charge resolution, timing resolution and lower dark rate than those of R3600 PMTs is confirmed before this study [2]. We also checked for safe operation in water and one month durability for power cycle of all prototype HPDs before the installation [2].
3.1. Photo-sensors for the test in the water tank 3.2. Configuration of the test As a preparatory step for the development of new 20-in. size HQE photo-sensors, we started the study of HQE application on the R3600 PMT. This is the first trial of HQE option for a 20-in. size
A 200-ton water tank is constructed for another proof-test of a Gd doped water Cherenkov detector in Kamioka mine, Japan.
154
S. Hirota et al. / Nuclear Instruments and Methods in Physics Research A 766 (2014) 152–155
The 240 R3600 PMTs are installed in the tank. We replaced 13 of R3600 PMTs with five HQE R3600 PMTs and eight 8-in. HPDs (Fig. 3). Photo-sensors in the tank are connected to Analog-Timing Module [4] with 70 m coaxial cables. This module records a integrated charge in 400 ns window and timing information at preset threshold, for each photo-sensor.
HPD (0.64 ns) [2] because it is limited by the pre-amplifier. An improvement of amplifier should be pursued in order to recover expected HPD performance, such as timing resolution under 1 ns. For HQE PMTs, dark rate tends to be decreasing after four month from the installation because of the operation in dark and stable circumstance whereas that of NQE PMT has been stabilized.
3.3. Latest result of the test We confirmed single photon peak of all new photo-sensors in the 200-ton tank. In order to emit photons uniformly in the tank, we set a diffuser ball at the center which is flashed by a laser diode. The dark rate of all photo-sensors was also measured. Typical single photo-electron charge distributions are shown in Fig. 4. The charge resolution of HPD is 32% which is better than that of PMTs, 43% for one sigma variation. The HPD has also better timing resolution as shown in Fig. 5. A shape of the timing distribution is fitted by the asymmetric Gaussian [3] and a value of sigma in the faster side is about 1.5 ns for HPD and 2.7 ns for both of NQE and HQE PMTs. Fig. 6 shows the distribution of dark rate at 0.5 photo-electron level after 4 months from the installation. Most of HPDs show lower dark rate than the average of that in NQE PMTs. Average dark rate of HQE is higher than that of NQE PMTs.
4. Discussion
Fig. 4. Typical charge distribution of 1 p.e. in the 200-ton tank. In case of HQE PMT, a 2 p.e. peak is contaminated because of its higher quantum efficiency than NQE PMTs. The luminosity of the light source was tuned to realize 1 p.e. level on NQE PMTs.
One HPD has failed within one month after installation. The failure was caused by break-down of its high voltage power supply. The operation of the HPD was once confirmed before the failure. The development of the high voltage power supply with the stable operation over ten years, required by the experiment, is necessary and on going. In single photo-electron charge distribution of the HPD, Fig. 4, we can see the broader pedestal than those of PMTs. This is caused by junction capacitance in the avalanche diode resulting in higher amplifier noise. Therefore a lower capacitance avalanche diode is under development. Also further development of pre-amplifier is necessary in terms of the durability and performance such as following. In terms of durability, our pre-amplifier should be tolerant of discharge just in case because HPDs are applied higher voltage and they cannot be fixed after the installation into HK even if they were broken. From the standpoint of performance, the measured timing resolution of HPD is worse than measured intrinsic value of 8-in.
Fig. 5. Typical transit time spread distribution of 1 p.e. in the 200-ton tank. The origin is the representative value of transit time in this measurement system. The timing resolution is obtained from the width of the peak.
Fig. 3. Position of tested photo-sensors.
S. Hirota et al. / Nuclear Instruments and Methods in Physics Research A 766 (2014) 152–155
155
5. Summary and prospect New photo-sensors are under development for Hyper-Kamiokande. A few-year term measurement of 8-in. HPDs and HQE PMTs in the 200-ton water tank began in September 2013. In this study, we measured both HPD and HQE PMT performance in the tank. The HPD shows better performance than PMTs. We will keep measuring over a few years. In parallel, 20-in. HQE HPD (R12850, HPK) and 20-in. HQE B&L type PMT (R12860, HPK) are under development and will be also tested in the tank. All studies will be completed by 2016 to select the photo-sensor of HK. References Fig. 6. Dark rate distribution of photo-sensors in the 200-ton tank after four months.
Monitoring of dark rate should be continue for a few years to confirm the long term stabilized value.
[1] K. Abe, et al., Hyper Kamiokande working group: Letter of Intent: The HyperKamiokande Experiment Detector Design and Physics Potential, arXiv:1109.3262v1. [2] S. Hirota, et al., Nuclear Instruments and Methods in Physics Research section A 732 (2013) 303. [3] K. Abe, et al., arXiv:1307.0162v2. [4] S. Fukuda, et al., Nuclear Instruments and Methods in Physics Research section A 501 (2003) 418.
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
New large aperture, hybrid photo-detector and photo multiplier tube for a gigantic water Cherenkov ring imaging detector Seiko Hirota a,n , Yasuhiro Nishimura b, Yusuke Suda c, Yuji Okajima d, Masato Shiozawa b, Shoei Nakayama b, Hidekazu Tanaka b, Yoshinari Hayato b, Motoyasu Ikeda b, Masayuki Nakahata b, Masashi Yokoyama c, Hiroaki Aihara c, Atsuko Ichikawa a, Akihiro Minamino a, Kunxian Huang a, Tsuyoshi Nakaya a, Yoshihiko Kawai e, Masatoshi Suzuki e, Takayuki Ohmura e a
Kyoto University, Department of Physics, Japan University of Tokyo, ICRR, Japan c University of Tokyo, Department of Physics, Japan d Tokyo Institute of Technology, Department of Physics, Japan e Hamamatsu Photonics K.K., Japan b
For the Hyper-Kamiokande working group art ic l e i nf o
a b s t r a c t
Available online 11 June 2014
We are developing a 20-in. aperture high quantum efficiency photo-multiplier tube (PMT) and a hybrid photo-detector (HPD) for Hyper-Kamiokande which is a next generation underground large water Cherenkov detector. We have measured prototypes of 20-in. PMT with a high quantum efficiency photocathode, 30% at 400 nm, and 8-in. HPDs with a normal quantum efficiency photocathode, 22% at 400 nm, in a 200-ton water tank and checked their performance. The PMTs have a 2.7 ns (sigma) timing resolution and 43% (sigma) charge resolution for single photo-electron. Compared to PMTs, HPDs show a better performance with a 1.7 ns timing resolution and 32. & 2014 The Authors. Published by Elsevier B.V. All rights reserved.
Keywords: Cherenkov ring imaging detector Hybrid photo-detector High quantum efficiency Hyper-Kamiokande Neutrino
1. Hyper-Kamiokande and requirements for photo-sensors
2. Photo-sensor development for HK
Hyper-Kamiokande (HK) is a next generation gigantic underground Cherenkov ring imaging detector designed to study a wide range of topics in physics and astrophysics related to neutrinos and proton decay [1]. It is a successor detector to Super-Kamiokande (SK) and consists of more than 100,000 photo-sensors and two cylindrical water tanks with one million tonnes mass in total. The requirements of photo-sensors for HK are a large aperture, a few nanoseconds timing resolution, single photon sensitivity and a few kHz dark rate. The timing resolution should be a few nanoseconds to realize a few tens of centimeters vertex resolution of HK in event reconstruction. The single photon sensitivity is required to observe neutrinos in the low energy region around several MeV, such as solar neutrinos and supernova neutrinos. Also the dark rate should be less than several kHz to suppress noise in low energy events.
Candidate photo-sensors for HK manufactured by Hamamatsu Photonics K.K. (HPK) are shown in Fig. 1 and their expected performance is listed in Table 1. In the baseline design of HK, the photo-sensors are the R3600 PMT which has been successfully used for over ten years in SK. The SK PMT has a venetian blind dynode which is used for a large aperture PMTs because a large dynode of this type can be made easily. This is based on an established technology but cost of photo-sensors with this design is high and would contribute onethird of total cost. For the reduction of cost, photo-coverage of HK is designed to be 20% which is half of SK. We are developing another type of PMT and hybrid photodetectors (HPDs) to pursue possibility of lower cost and higher performance than the first candidate. We also aim to make quantum efficiency higher for all candidates in order to try an additional cost saving by reducing the number of photo-sensors while maintaining the photo-detection efficiency.
n
Corresponding author. E-mail address: [email protected] (S. Hirota).
http://dx.doi.org/10.1016/j.nima.2014.06.010 0168-9002/& 2014 The Authors. Published by Elsevier B.V. All rights reserved.
S. Hirota et al. / Nuclear Instruments and Methods in Physics Research A 766 (2014) 152–155
153
Fig. 1. Hyper-Kamiokande photo-sensor candidates.
Table 1 Estimated performance of 20-in. photo-sensor candidates for HK.
Amplification QE CE 1 p.e.b separation (Peak to Valley ratio) Timing resolution (FWHM) Gain HV a b c
SK PMT (R3600 HPK)
B&L PMT (R12860 HPK)
HPD (R12850 HPK)
Venetian blind dynode 22%a 80% 1.4 5.5 ns 106–107 2 kV
Box and line dynode 30% 93% 2:5 2.7 ns 106–107 2 kV
Avalanche diode 30% 95% 3 0.75 ns 104–105 8 kVc
HQE R3600 can achieve 30% quantum efficiency. Photo-electron. The electric potential around the AD is 8 kV and the bias voltage of the AD is about 300 V.
2.1. Box-and-line PMT A new PMT design with a box and line (B&L) dynode has been developed to improve timing resolution and collection efficiency compared to SK PMT with the venetian blind type. 2.2. HPD An HPD is a hybridization of a photo tube and an avalanche diode (AD). Due to the smaller gain than PMTs, HPDs need preamplifiers. However, the HPD has a better single photon charge resolution than that of PMTs because the initial amplification of an HPD is larger than those of PMTs [2]. The timing resolution and collection efficiency are also better than that of PMTs due to higher voltage of 8 kV. Moreover using AD instead of dynode may lead to the reduction of cost because the dynode is significant fraction of the cost of a PMT.
3. Test in a 200-ton water tank We have been testing new photo-sensors in a 200-ton water tank from autumn 2013. Our goal is to confirm stable operation of new photo-sensors over a few years in the water tank because they have not previously been used in a water. The stability of performance such as single photon resolution in charge, timing resolution and dark rate are monitored. Of particular interest is how much the dark rate of a high quantum efficiency (HQE) PMT reduces in the water tank because thermal electrons from the photo-cathode are the main source of dark rate above single photo-electron level.
Fig. 2. Quantum Efficiency of HQE R3600 PMT samples for the first proof-test.
PMT. We will equip other candidates with HQE photocathode based on this study. Eight HQE R3600 PMTs were produced and have the peak quantum efficiency about 30% (Fig. 2). Also a normal quantum efficiency (NQE) HPD prototype has been developed for the test with an 8-in. diameter size which is the same size as photo-sensors to be used in the veto layer of HK. The 8-in. prototype HPD modules are equipped with pre-amplifiers and a high voltage power supply on the back side, covered by a water-proof housing. The HV power supply is operated by a low voltage of 5 V to avoid exposure of 8 kV line in water. The better performance such as single photo-electron charge resolution, timing resolution and lower dark rate than those of R3600 PMTs is confirmed before this study [2]. We also checked for safe operation in water and one month durability for power cycle of all prototype HPDs before the installation [2].
3.1. Photo-sensors for the test in the water tank 3.2. Configuration of the test As a preparatory step for the development of new 20-in. size HQE photo-sensors, we started the study of HQE application on the R3600 PMT. This is the first trial of HQE option for a 20-in. size
A 200-ton water tank is constructed for another proof-test of a Gd doped water Cherenkov detector in Kamioka mine, Japan.
154
S. Hirota et al. / Nuclear Instruments and Methods in Physics Research A 766 (2014) 152–155
The 240 R3600 PMTs are installed in the tank. We replaced 13 of R3600 PMTs with five HQE R3600 PMTs and eight 8-in. HPDs (Fig. 3). Photo-sensors in the tank are connected to Analog-Timing Module [4] with 70 m coaxial cables. This module records a integrated charge in 400 ns window and timing information at preset threshold, for each photo-sensor.
HPD (0.64 ns) [2] because it is limited by the pre-amplifier. An improvement of amplifier should be pursued in order to recover expected HPD performance, such as timing resolution under 1 ns. For HQE PMTs, dark rate tends to be decreasing after four month from the installation because of the operation in dark and stable circumstance whereas that of NQE PMT has been stabilized.
3.3. Latest result of the test We confirmed single photon peak of all new photo-sensors in the 200-ton tank. In order to emit photons uniformly in the tank, we set a diffuser ball at the center which is flashed by a laser diode. The dark rate of all photo-sensors was also measured. Typical single photo-electron charge distributions are shown in Fig. 4. The charge resolution of HPD is 32% which is better than that of PMTs, 43% for one sigma variation. The HPD has also better timing resolution as shown in Fig. 5. A shape of the timing distribution is fitted by the asymmetric Gaussian [3] and a value of sigma in the faster side is about 1.5 ns for HPD and 2.7 ns for both of NQE and HQE PMTs. Fig. 6 shows the distribution of dark rate at 0.5 photo-electron level after 4 months from the installation. Most of HPDs show lower dark rate than the average of that in NQE PMTs. Average dark rate of HQE is higher than that of NQE PMTs.
4. Discussion
Fig. 4. Typical charge distribution of 1 p.e. in the 200-ton tank. In case of HQE PMT, a 2 p.e. peak is contaminated because of its higher quantum efficiency than NQE PMTs. The luminosity of the light source was tuned to realize 1 p.e. level on NQE PMTs.
One HPD has failed within one month after installation. The failure was caused by break-down of its high voltage power supply. The operation of the HPD was once confirmed before the failure. The development of the high voltage power supply with the stable operation over ten years, required by the experiment, is necessary and on going. In single photo-electron charge distribution of the HPD, Fig. 4, we can see the broader pedestal than those of PMTs. This is caused by junction capacitance in the avalanche diode resulting in higher amplifier noise. Therefore a lower capacitance avalanche diode is under development. Also further development of pre-amplifier is necessary in terms of the durability and performance such as following. In terms of durability, our pre-amplifier should be tolerant of discharge just in case because HPDs are applied higher voltage and they cannot be fixed after the installation into HK even if they were broken. From the standpoint of performance, the measured timing resolution of HPD is worse than measured intrinsic value of 8-in.
Fig. 5. Typical transit time spread distribution of 1 p.e. in the 200-ton tank. The origin is the representative value of transit time in this measurement system. The timing resolution is obtained from the width of the peak.
Fig. 3. Position of tested photo-sensors.
S. Hirota et al. / Nuclear Instruments and Methods in Physics Research A 766 (2014) 152–155
155
5. Summary and prospect New photo-sensors are under development for Hyper-Kamiokande. A few-year term measurement of 8-in. HPDs and HQE PMTs in the 200-ton water tank began in September 2013. In this study, we measured both HPD and HQE PMT performance in the tank. The HPD shows better performance than PMTs. We will keep measuring over a few years. In parallel, 20-in. HQE HPD (R12850, HPK) and 20-in. HQE B&L type PMT (R12860, HPK) are under development and will be also tested in the tank. All studies will be completed by 2016 to select the photo-sensor of HK. References Fig. 6. Dark rate distribution of photo-sensors in the 200-ton tank after four months.
Monitoring of dark rate should be continue for a few years to confirm the long term stabilized value.
[1] K. Abe, et al., Hyper Kamiokande working group: Letter of Intent: The HyperKamiokande Experiment Detector Design and Physics Potential, arXiv:1109.3262v1. [2] S. Hirota, et al., Nuclear Instruments and Methods in Physics Research section A 732 (2013) 303. [3] K. Abe, et al., arXiv:1307.0162v2. [4] S. Fukuda, et al., Nuclear Instruments and Methods in Physics Research section A 501 (2003) 418.