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Photomultiplier Tube System for the Daya Bay Experiment
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Nuclear Physics B (Proc. Suppl.) 229–232 (2012) 438 www.elsevier.com/locate/npbps
Photomultiplier Tube System for the Daya Bay Experiment Weili Zhong, for the Daya Bay Collaboration Lawrence Berkeley National Laboratory, Mail Stop 50A-2161, Berkeley CA 94720, USA
Abstract The Daya Bay Reactor Neutrino Experiment is designed to measure sin2 (2θ13 ) to 0.01 by performing a relative measurement of electron antineutrino events via inverse β decay in the near and far detectors. The antineutrino detectors will be placed in water pools and surrounded by at least 2.5m of water to suppress background. The water pools also serve as Cherenkov detectors for tagging cosmic-ray muons that can generate background. Details of the photomultiplier tube assemblies used in the antineutrino detectors and the water Cherenkov counters are presented. Keywords: Daya Bay, antineutrino detector, water pool, photomultiplier tube, waterproof, oil-proof The Daya Bay experiment [1] has eight antineutrino detectors (ADs) at three experimental sites, with two detectors at each of the two near sites and four at the far site. In each AD, 192 Hamamatsu R5912 8” photomultiplier tube (PMT) oil-proof assemblies are distributed along the side walls of steel tanks to detect optical photons. The antineutrino detectors are placed in water pools that surround the ADs by at least 2.5m of water to shield them from γ and neutrons. 944 8” PMT in the water pools serve as Cherenkov detectors to tag comic muons. 608 of the 944 waterproof assemblies are Hamamatsu 8” PMTs. The rest are custom-built EMI waterproof assemblies. The EMI tubes had been used in the MACRO experiment. Both of the Hamamatsu waterproof and oil-proof assemblies can withstand three atmospheres of pressure, and the MACRO waterproof assemblies have been tested under 6 to 12 psi gauge pressure. The PMTs are operated with positive high voltage, which is supplied by 1934A High Voltage (HV) modules in CAEN SY1527LC Mainframes. For each tube, the HV and PMT signals are carried by the same cable and decoupled by a splitter box. We made detailed studies of the performance of these PMTs to determine operating parameters. These are: Gain (2×107 ), SPE (P/V>2.5 at a gain of 107 ), linearity (nonlinearity<2%@40mA with tapered base), pre-pulse 0920-5632/$ – see front matter © 2012 Published by Elsevier B.V. doi:10.1016/j.nuclphysbps.2012.09.075
(PPR <2% for s.p.e. main pulse) and after-pulse (APR <10% for s.p.e. main pulse), rise time (<6.5ns) and fall time (<10ns), and quantum efficiency (>25%@420nm), etc. We built a PMT testing facility to test the performance of each PMT, and to check whether the requirements were met. A few failed tubes whose test results didn’t meet the requirements were sent back to the manufacture for replacement. Besides the testing, we also study the after-pulse time distribution, charge spectrum and rate versus signal pulse charge in detail. Special magnetic shields are used to reduce the charge variation due to the effect of earth’s magnetic field. When mounting the PMTs in the ADs, we picked out the oil-proof PMTs randomly from the available pool to make sure that PMT properties in eight ADs are statistically identical. Oil-proof PMT assemblies are held in individual mounts and secured in a PMT support structure, and installed on ladder-like frames in the steel tanks of the ADs. The Muon PMTs are secured in Tshaped frames and then installed onto standing structures in the water pools. After the detectors are assembled, PMT performance is monitored with calibration system. Some characteristics are also monitored by the realtime monitoring system. [1] X.Guo et al. [Daya-Bay Collaboration], arXiv:hep-ex/0701029.
Nuclear Physics B (Proc. Suppl.) 229–232 (2012) 438 www.elsevier.com/locate/npbps
Photomultiplier Tube System for the Daya Bay Experiment Weili Zhong, for the Daya Bay Collaboration Lawrence Berkeley National Laboratory, Mail Stop 50A-2161, Berkeley CA 94720, USA
Abstract The Daya Bay Reactor Neutrino Experiment is designed to measure sin2 (2θ13 ) to 0.01 by performing a relative measurement of electron antineutrino events via inverse β decay in the near and far detectors. The antineutrino detectors will be placed in water pools and surrounded by at least 2.5m of water to suppress background. The water pools also serve as Cherenkov detectors for tagging cosmic-ray muons that can generate background. Details of the photomultiplier tube assemblies used in the antineutrino detectors and the water Cherenkov counters are presented. Keywords: Daya Bay, antineutrino detector, water pool, photomultiplier tube, waterproof, oil-proof The Daya Bay experiment [1] has eight antineutrino detectors (ADs) at three experimental sites, with two detectors at each of the two near sites and four at the far site. In each AD, 192 Hamamatsu R5912 8” photomultiplier tube (PMT) oil-proof assemblies are distributed along the side walls of steel tanks to detect optical photons. The antineutrino detectors are placed in water pools that surround the ADs by at least 2.5m of water to shield them from γ and neutrons. 944 8” PMT in the water pools serve as Cherenkov detectors to tag comic muons. 608 of the 944 waterproof assemblies are Hamamatsu 8” PMTs. The rest are custom-built EMI waterproof assemblies. The EMI tubes had been used in the MACRO experiment. Both of the Hamamatsu waterproof and oil-proof assemblies can withstand three atmospheres of pressure, and the MACRO waterproof assemblies have been tested under 6 to 12 psi gauge pressure. The PMTs are operated with positive high voltage, which is supplied by 1934A High Voltage (HV) modules in CAEN SY1527LC Mainframes. For each tube, the HV and PMT signals are carried by the same cable and decoupled by a splitter box. We made detailed studies of the performance of these PMTs to determine operating parameters. These are: Gain (2×107 ), SPE (P/V>2.5 at a gain of 107 ), linearity (nonlinearity<2%@40mA with tapered base), pre-pulse 0920-5632/$ – see front matter © 2012 Published by Elsevier B.V. doi:10.1016/j.nuclphysbps.2012.09.075
(PPR <2% for s.p.e. main pulse) and after-pulse (APR <10% for s.p.e. main pulse), rise time (<6.5ns) and fall time (<10ns), and quantum efficiency (>25%@420nm), etc. We built a PMT testing facility to test the performance of each PMT, and to check whether the requirements were met. A few failed tubes whose test results didn’t meet the requirements were sent back to the manufacture for replacement. Besides the testing, we also study the after-pulse time distribution, charge spectrum and rate versus signal pulse charge in detail. Special magnetic shields are used to reduce the charge variation due to the effect of earth’s magnetic field. When mounting the PMTs in the ADs, we picked out the oil-proof PMTs randomly from the available pool to make sure that PMT properties in eight ADs are statistically identical. Oil-proof PMT assemblies are held in individual mounts and secured in a PMT support structure, and installed on ladder-like frames in the steel tanks of the ADs. The Muon PMTs are secured in Tshaped frames and then installed onto standing structures in the water pools. After the detectors are assembled, PMT performance is monitored with calibration system. Some characteristics are also monitored by the realtime monitoring system. [1] X.Guo et al. [Daya-Bay Collaboration], arXiv:hep-ex/0701029.