Large Area MCP-PMT and its Application at JUNO Yifang Wang For the MCP-PMT development group Institute of High Energy Physics NeuTel 2017, Venice

The JUNO Experiment Key Issue：How to get sE < 3%/√E  1200 PE/MeV ? Vito’s talk Yangjiang NPP Taishan NPP Daya Bay NPP Huizhou NPP Lufeng NPP 53 km Hong Kong Macau Guang Zhou Shen Zhen Zhu Hai 2.5 h drive Daya Bay JUNO 20 kt LS Previous site candidate J. Phys. G 43: 030401 (2016) (arXiv:1507.05613) Talk by YFW at ICFA seminar 2008, Neutel 2011; Key Issue：How to get sE < 3%/√E  1200 PE/MeV ?

How to Get Enough Photons KamLAND JUNO Needed gain Light yield 250 p.e./MeV 1200 p.e./MeV 5 Photocathode coverage 34% 75% 2.2 1.5g/l PPO 3-5g/l PPO 1.5 Attenuation length/R 15 m/16m 25m/35m ~ 0.8 PMT QE*CE 20%*60% ？ ~ 2 Where to get a factor of 2 increase for Quantum Efficiency(QE)* Collection Efficiency(CE) ?

New type of PMTs under-development in ~2009 Reflective photocathode by UC Davis, Higher QE Dynode replaced by Scintillator/APD Large Area picosecond photo detectors(LAPPD) Hamamatsu Production：X-HPD， 8” and 13”; 18KV HV

High QE PMTs in ~ 2008 SBA/UBA/EBA/GaAsP Good enough QE for PMTs ? 35%/45%/55%/50% Good enough QE for PMTs ? Good enough for 20” PMTs ? Good enough price ? 2018/6/17

Our Proposal: MCP-based PMTs Advantages: Higher QE: transmmissive photocathode at top + reflective photocathode at bottom High CE: less shadowing effect Easy for production: less manual operation and steps Good MCP production capabilities in China Disadvantages: Higher cost ? No one knows how to make it

First Attempt: A Prototype by 2011 Partnership with a research institute Prototypes: signal barely seen, low gain, low QE, high noise, … no hope for production, … 5” MCP-PMT Spectral Response 300~ 650nm Anode Dark Current < 100nA Cathode luminous sensitivity > 50 uA/Lm Gain > 1.0*105

New Collaboration Established 1/3 MCP of the world Setup groups Design & simulation Photocathode & metal film MCP production & pre-processing Glass bulb & low radioactive backgrounds Other components Assembly & vacuum sealing Testing & evaluation Setup roadmap quit very soon 5”(8”) Prototype 20” Prototype Production Bylaws, management, … Weekly phone meetings Bi-monthly general meeting Design 2009 2010~2013 2013~2015 2016~2019

Design and Simulation 8” and 20” PMTs Bulb Shape & MCP position Voltage setting and optimization Focusing field shape，location and voltage setting Collection efficiency, timing, geomagnetic field effect, etc. Collection efficiency

MCP Production & Pre-processing MCP parameters: size, hole diameter & depth(detector type), bulk resistance,etc. Surface treatment & electron cleaning Electrode: depth, shape, materials, … Low cost: production process, quality control, selection criteria, … Microchannel Plate response Simulation

Photocathode Art: thin layers of K-Cs-Sb Alkali source: materials, shape, evaporation process, etc. Vacuum equipment: monitoring and control during production Quality: consistency, uniformity, … QE ~ 29%@410nm Cathode current  QE

Glass bulb, Transition Section and Kovar Skilled workers: manual blowing Glass: hardness, thermal expansion, K free, water compatible, etc. Oven, welding with Kovar, … Low radioactive backgrounds: material, process, environment, … Mechanical design and Shape optimization

MCP-PMT Assembly Process

Prototypes and Failures After a few years with a lot of troubles, we start to get prototypes: Photocathode, MCP assembly, vacuum sealing,… Reasonable signals & good properties But major issues: Gain of MCPs are not the same cannot have two independent MCPs giving output signals CE very much dependent on Incident angle New focusing field Too low CE Surface treatment Dead bodies

New Design & Improved CE Horizontal collection surface: one output New surface treatment of MCP: CE increased from ~60% to ~100% Better than dynode which has a 10% loss due to the field mesh Such MCP-PMT has a better CE but worse timing Dynode: A mesh over the dynode, CE ~ 90%

Tests Mechanical: Glass bulb under pressure, welding with Kovar, vacuum, compatibility with water, etc MCP Aging Collection efficiency: angular dependence radioactive backgrounds 30% Gain lost @24C  500 yrs Angular response Component WT% 238U (Bq/kg) 232Th (Bq/kg) 40K (Bq/kg) Glass bulb 89.48 0.87/0.78 0.38/0.34 0.2/0.18 Transition section 2.82 1.74/0.05 0.45/0.01 10.1/0.28 Others 7.7 Negligible Total 100 ~0.83 ~0.35 ~0.46 Requirement 0.93 0.30 0.96

Performance QE & uniformity Dark rate After pulse Min:24.5%; Max:29% Average:26.5%

Main Difference with Hamamatsu 1ns spread 6ns spread TTS at top ~90% ~100% Relativity detection efficiency: Hamamatsu R12860 MCP-PMT

reflection+ transmission Performance Summary Characteristics unit MCP-PMT（IHEP） R12860(Hamamatsu) Electron Multiplier -- MCP Dynode Photocathode mode reflection+ transmission transmission Quantum Efficiency（400nm） % 26 (T), 30 (T+R) 30(T) Relativity Detection Efficiency ~ 110% ~ 100% P/V of SPE ＞ 3 TTS on the top point ns ~12 ~3 Rise time/ Fall time R~2 , F~10 R~7 , F~17 Anode Dark Count Hz ~30K After Pulse Time distribution us 4.5 4, 17 After Pulse Rate 3 10 Glass Low-Potassium Glass HARIO-32

PMT Purchasing of JUNO Dec.16, 2015 Characteristics unit MCP-PMT（NNVC） R12860（Hamamatsu） Detection Efficiency (QE*CE*area) % 27%, > 24% P/V of SPE 3.5, > 2.8 3, > 2.5 TTS on the top point ns ~12, < 15 2.7, < 3.5 Rise time/ Fall time R~2, F~12 R~5,F~9 Anode Dark Count Hz 20K, < 30K 10K, < 50K After Pulse Rate 1, <2 10, < 15 Radioactivity of glass ppb 238U:50 232Th:50 40K: 20 238U:400 232Th:400 40K: 40 15k MCP-PMT (75%) from NNVT 5k Dynode(25%) from Hamamatzu By Scaling PMT Spec for LS quantity to reach 3s@ 6year  Decision based on risk, price, performance merit for physics

Mass Production at NNVT

Pilot Production Production equipment all in hands Training workers, tuning equipment All parts in hand A few hundreds of products Gain vs HV first batch by workers CE*QE Radioactivity of glass P/V

Summary Driven by JUNO, we develop a new type of PMTs based on MCP New design, new technology Potentially better performance than PMTs based on Dynode Its performance satisfied JUNO requirements Based on a model to maximize Physics*Price/Risk, JUNO signed contract to purchase ¼ PMTs from Hamamatsu and ¾ from NNVT Mass production started at NNVT & Hamamatsu for JUNO We started from a wrong design but ended up a good product

PMT Selection Maximize: Sum(Scores*S*F) Scale PMT Spec for LS quantity to reach 3s@ 6year QE Dark rate Radioactivity After pulsing TTS Unit Price Safety factor(S) Award fraction(F) x, 1-x (PQE)A=(ε-27)×3.518 (PDN)A=(20-DN)×0.118 Maximize: Sum(Scores*S*F) 30×(2.5-P) （1-0.15x）, (1-0.15(1-x))