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Developement of Hybrid Photo-detectors for the Hyper-Kamiokande Experiment
Available online at www.sciencedirect.com
Nuclear Physics B (Proc. Suppl.) 253–255 (2014) 208–209 www.elsevier.com/locate/npbps
Developement of Hybrid Photo-detectors for the Hyper-Kamiokande Experiment Seiko Hirotaa , Yasuhiro Nishimurab , Shoei Nakayamab , Isao Kametanib , Masato Shiozawab , Yoichiro Suzukib , Hiroyuki Sekiyab , Masayuki Nakahatab , Yoshinari Hayatob , Yuto Hagab , Makoto Miurab , Atsuko Ichikawaa , Motoyasu Ikedaa , Tsuyoshi Nakayaa , Akihiro Minaminoa , Keiji Tateishia , Hiroaki Aiharac , Yusuke Sudac , Masashi Yokoyamac , Takayuki Omurad , Yoshihiko Kawaid , Masatoshi Suzukid , Mark Robert Vagins1 a Kyoto
University, Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto-city, Kyoto, Japan b ICRR, Kashiwanoha 5-1-5, Kashiwa-sity, Chiba, Japan c University of Tokyo, Hongo 7-3-1, Bunkyo-Ku, Tokyo, Japan d Hamamatsu K.K., Sunayama-cho, 325-6, Naka-ku, Hamamatsu-city, Shizuoka, Japan e Kavli IPMU, Kashiwanoha 5-1-5, Kashiwa-sity, Chiba, Japan
Abstract We are developing a hybrid photo detector (HPD) for the Hyper-Kamiokande Project. Eight-inch HPDs were prepared to evaluate their performance. Based on the results from these measurements, HPDs achieve a better performance such as single photon separation than conventional PMTs. A verification study lasting a few years in a water tank is planned in 2013 to check their feasibility. Keywords: Hyper-Kamiokande, Photo Detector, Neutrino, Cherenkov Detector
1. Hyper-Kamiokande Hyper-Kamiokande is a next-generation underground water Cherenkov detector designed to study a wide range of topics in physics and astronomy. Its total (fiducial) volume is 1.0 (0.56) million metric tons, which is 20 (25) times larger than that of SuperKamiokande. Accordingly, in its baseline design the Hyper-Kamiokande detector requires 100,000 20-inch and 25,000 8-inch PMTs, almost 10 times as many as Super-Kamiokande [1]. The excellent performance and low production cost are crucial for the Hyper-Kamiokande detector. Therefore the photosensor for Hyper-Kamiokande is requiered to have a large photo-cathode area to realize wide photo-coverage with a small number of detectors. Moreover single photoelectron must be clearly separated for a long run over tens years. 2. Principle of a hybrid photo-detector The HPD is a hybridization of a photomultiplier tube and an avalanche diode (AD) that can possibly achieve http://dx.doi.org/10.1016/j.nuclphysbps.2014.09.052 0920-5632/© 2014 Published by Elsevier B.V.
both of low cost and excellent performance. The amplification system of HPD is different from a normal PMT using dynode. Figure 1 shows that HPD has a photo cathode like a standard PMT and a avalanche diode. Therefore amplification consists of two steps; bombardment from the photocathode to the AD surface under higher voltage (∼8 kV) and then an avalanche at AD. Because of the large bombardment gain (about 400) and a fast electron propagation, the HPD is expected to show better photon counting efficiency and timing resolution than conventional PMTs. In addition, the mass production cost is expected to be lower thanks to the simple structure of AD compared to the dynode of a standard PMT. 3. Research and development of HPD There is something to consider concerning using HPDs in Hyper-Kamiokande; HPDs have never been used in water and for neutrino detection though they must be applied higher voltage. Therefore we need to confirm the operation of HPDs and their feasibility in a water Cherenkov detector over long periods by measur-
209
S. Hirota et al. / Nuclear Physics B (Proc. Suppl.) 253–255 (2014) 208–209
Avalanche Diode (AD) ~260V
"
ΔV ~ -260V ~8kV
! ~400
× ~100 × ~!
Figure 1: Left: Schematic diagram of HPD, Center: Set Up for measurements, Right: Wave form
ing performance of eight 8-inch HPDs relative to 232 PMTs in the tank. We plan to perform such studies in a 200-ton water tank starting spring 2013 and a fewyears operation is planning. First, we have started using a smaller HPD (8-inch), and then we will promote the development of 20-inch HPDs based on the results from measurements of 8-inch HPDs. 3.1. Basic performance measurements of 8-inch HPDs
An 8-inch HPD has been developed by Hamamatsu Photonics K.K. We measured several characteristics of them. The measurement uses a preamp and a 70m cable as shown in Figure 1. Figure 1 shows the signal produced by an HPD when 1 or 2 photons from a laser diode (OPG-1000-NIM, 405nm) are detected. We can distinguish single photon waveform from others better than with standard PMTs. Figure 2 shows the separation of the first and second photoelectrons by pulse height. The peak to valley ratio, which contributes to the trigger performance, is about 6. The performance of the HPD is better than that of 20-inch PMT which typical value is 1.4. It provides a clearer criteria to determine the HPD threshold at valley, which is related to data taking trigger rate. The expected depending of the gain on high voltage and bias of HPDs are got as shown in Figure 3.
Gain = 1.04 ×10 4 ×
1 0.0015 ⎛ V ⎞ 1− ⎜ ⎟ ⎝ 377 ⎠
Figure 3: Gain depends on both HV and Bias. , Left: On HV, Right: On Bias, Red lines: Fitting results
3.2. Confirmation of stable operation of HPDs before long term verification study in 200-ton tank Before the implementation of the verification study in 200-ton tank, we want to confirm stable operation of HPDs over long periods both in and out water. We monitored a fluctuation of pulse height and observed charge with LED, to check an HPD’s gain stability for a few days. It was stable within 1 %. Now we are going to test its more detailed and longer term stability for months. Also we have applied power cycle to HPDs and check durability of turing them on and off many times to avoid breakdown of HPDs after installation into a tank where we can not replace them to new one easily. After a short term operation check of an HPD in water, the installation of HPDs and PMTs in 200-ton tank located in the Kamioka mine will start in spring 2013. 4. Summary
Development of HPDs for Hyper-Kamiokande is on going. Better performances such as single photon separation are confirmed. The verification study in a Cherenkov detector will start in 2013.
Figure 2: Pulse Height Distribution
Based on these features, HPDs can be a stronger candidate of photo detectors in Hyper-Kamiokande than conventional PMTs.
References [1] K.Abe et al. (Hyper Kamiokande working group): Letter of Intent: The Hyper-Kamiokande Experiment -Detector Design and Physics Potential- , arXiv:1109.3262v1
Nuclear Physics B (Proc. Suppl.) 253–255 (2014) 208–209 www.elsevier.com/locate/npbps
Developement of Hybrid Photo-detectors for the Hyper-Kamiokande Experiment Seiko Hirotaa , Yasuhiro Nishimurab , Shoei Nakayamab , Isao Kametanib , Masato Shiozawab , Yoichiro Suzukib , Hiroyuki Sekiyab , Masayuki Nakahatab , Yoshinari Hayatob , Yuto Hagab , Makoto Miurab , Atsuko Ichikawaa , Motoyasu Ikedaa , Tsuyoshi Nakayaa , Akihiro Minaminoa , Keiji Tateishia , Hiroaki Aiharac , Yusuke Sudac , Masashi Yokoyamac , Takayuki Omurad , Yoshihiko Kawaid , Masatoshi Suzukid , Mark Robert Vagins1 a Kyoto
University, Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto-city, Kyoto, Japan b ICRR, Kashiwanoha 5-1-5, Kashiwa-sity, Chiba, Japan c University of Tokyo, Hongo 7-3-1, Bunkyo-Ku, Tokyo, Japan d Hamamatsu K.K., Sunayama-cho, 325-6, Naka-ku, Hamamatsu-city, Shizuoka, Japan e Kavli IPMU, Kashiwanoha 5-1-5, Kashiwa-sity, Chiba, Japan
Abstract We are developing a hybrid photo detector (HPD) for the Hyper-Kamiokande Project. Eight-inch HPDs were prepared to evaluate their performance. Based on the results from these measurements, HPDs achieve a better performance such as single photon separation than conventional PMTs. A verification study lasting a few years in a water tank is planned in 2013 to check their feasibility. Keywords: Hyper-Kamiokande, Photo Detector, Neutrino, Cherenkov Detector
1. Hyper-Kamiokande Hyper-Kamiokande is a next-generation underground water Cherenkov detector designed to study a wide range of topics in physics and astronomy. Its total (fiducial) volume is 1.0 (0.56) million metric tons, which is 20 (25) times larger than that of SuperKamiokande. Accordingly, in its baseline design the Hyper-Kamiokande detector requires 100,000 20-inch and 25,000 8-inch PMTs, almost 10 times as many as Super-Kamiokande [1]. The excellent performance and low production cost are crucial for the Hyper-Kamiokande detector. Therefore the photosensor for Hyper-Kamiokande is requiered to have a large photo-cathode area to realize wide photo-coverage with a small number of detectors. Moreover single photoelectron must be clearly separated for a long run over tens years. 2. Principle of a hybrid photo-detector The HPD is a hybridization of a photomultiplier tube and an avalanche diode (AD) that can possibly achieve http://dx.doi.org/10.1016/j.nuclphysbps.2014.09.052 0920-5632/© 2014 Published by Elsevier B.V.
both of low cost and excellent performance. The amplification system of HPD is different from a normal PMT using dynode. Figure 1 shows that HPD has a photo cathode like a standard PMT and a avalanche diode. Therefore amplification consists of two steps; bombardment from the photocathode to the AD surface under higher voltage (∼8 kV) and then an avalanche at AD. Because of the large bombardment gain (about 400) and a fast electron propagation, the HPD is expected to show better photon counting efficiency and timing resolution than conventional PMTs. In addition, the mass production cost is expected to be lower thanks to the simple structure of AD compared to the dynode of a standard PMT. 3. Research and development of HPD There is something to consider concerning using HPDs in Hyper-Kamiokande; HPDs have never been used in water and for neutrino detection though they must be applied higher voltage. Therefore we need to confirm the operation of HPDs and their feasibility in a water Cherenkov detector over long periods by measur-
209
S. Hirota et al. / Nuclear Physics B (Proc. Suppl.) 253–255 (2014) 208–209
Avalanche Diode (AD) ~260V
"
ΔV ~ -260V ~8kV
! ~400
× ~100 × ~!
Figure 1: Left: Schematic diagram of HPD, Center: Set Up for measurements, Right: Wave form
ing performance of eight 8-inch HPDs relative to 232 PMTs in the tank. We plan to perform such studies in a 200-ton water tank starting spring 2013 and a fewyears operation is planning. First, we have started using a smaller HPD (8-inch), and then we will promote the development of 20-inch HPDs based on the results from measurements of 8-inch HPDs. 3.1. Basic performance measurements of 8-inch HPDs
An 8-inch HPD has been developed by Hamamatsu Photonics K.K. We measured several characteristics of them. The measurement uses a preamp and a 70m cable as shown in Figure 1. Figure 1 shows the signal produced by an HPD when 1 or 2 photons from a laser diode (OPG-1000-NIM, 405nm) are detected. We can distinguish single photon waveform from others better than with standard PMTs. Figure 2 shows the separation of the first and second photoelectrons by pulse height. The peak to valley ratio, which contributes to the trigger performance, is about 6. The performance of the HPD is better than that of 20-inch PMT which typical value is 1.4. It provides a clearer criteria to determine the HPD threshold at valley, which is related to data taking trigger rate. The expected depending of the gain on high voltage and bias of HPDs are got as shown in Figure 3.
Gain = 1.04 ×10 4 ×
1 0.0015 ⎛ V ⎞ 1− ⎜ ⎟ ⎝ 377 ⎠
Figure 3: Gain depends on both HV and Bias. , Left: On HV, Right: On Bias, Red lines: Fitting results
3.2. Confirmation of stable operation of HPDs before long term verification study in 200-ton tank Before the implementation of the verification study in 200-ton tank, we want to confirm stable operation of HPDs over long periods both in and out water. We monitored a fluctuation of pulse height and observed charge with LED, to check an HPD’s gain stability for a few days. It was stable within 1 %. Now we are going to test its more detailed and longer term stability for months. Also we have applied power cycle to HPDs and check durability of turing them on and off many times to avoid breakdown of HPDs after installation into a tank where we can not replace them to new one easily. After a short term operation check of an HPD in water, the installation of HPDs and PMTs in 200-ton tank located in the Kamioka mine will start in spring 2013. 4. Summary
Development of HPDs for Hyper-Kamiokande is on going. Better performances such as single photon separation are confirmed. The verification study in a Cherenkov detector will start in 2013.
Figure 2: Pulse Height Distribution
Based on these features, HPDs can be a stronger candidate of photo detectors in Hyper-Kamiokande than conventional PMTs.
References [1] K.Abe et al. (Hyper Kamiokande working group): Letter of Intent: The Hyper-Kamiokande Experiment -Detector Design and Physics Potential- , arXiv:1109.3262v1