Improved PMTs for the Cherenkov Telescope Array project Razmik Mirzoyan for the Focal Plane Instrumentation WG Max-Planck-Institute for Physics Munich, Germany Razmik Mirzoyan: Improved PMTs forthe CTA Project 11 June 2011, TIPP-2011, Chicago, USA 1

Cherenkov Telescope Array (CTA) Core people: MAGIC, H.E.S.S. and VERITAS collaborations An initiative to build the next generation large ground – based gamma ray instrument of ~ 10 times higher sensitivity 840 scientists from > 100 institutions (EU, USA and Japan) Study distant AGNs, Black Holes, Gamma Ray Bursts, as well as the galactic sources (Pulsars, Supernovae, µquasar,…) from 10 GeV to 100 TeV Answer the long-standing question about the origin of cosmic rays ~100 telescopes, 2-arrays (in S & N) Site search ongoing for Very High Energy Ground-Based  -ray Astronomy 11 June 2011, TIPP-2011, Chicago, USA 2 Razmik Mirzoyan: Improved PMTs forthe CTA Project

11 June 2011, TIPP-2011, Chicago, USA Razmik Mirzoyan: Improved PMTs forthe CTA Project 3 3 types of telescopes are planned: several large 23m, many mid-size 12m and many small ~(4-7)m Standard sensor: PMTs (SiPM: candidate sensor) Cherenkov Telescope Array (CTA)

Quantum Efficiency measurements Razmik Mirzoyan: Improved PMTs forthe CTA Project CompanyType QEpeak( ) Cher Hamamatsu8619 1“ 28,7 ± 2,2 (390 nm) 19,4 ± 0,3 Hamamatsu9420 1,5“ 34,6 ± 3,1 (370 nm) 22,9 ± 0,4 Hamamatsu7724 2“ 38,9 ± 3,3 (370 nm) 25,7 ± 0,4 Electron Tubes 9117B 1,5“ 34,0 ± 3,2 (360 nm) 19,9 ± 0,3 Electron Tubes 9142B 1,125“ 30,2 ± 2,7 (370 nm) 16,5 ± 0,3 11 June 2011, TIPP-2011, Chicago, USA 4

Razmik Mirzoyan: Improved PMTs forthe CTA Project 1.5’ size, super-bialkali candidate PMTs Hamamatsu R9420 modified (convex input window shape) (mat and polished input window types) Hamamatsu R8619 modified Body of R9420 but used 8619 dynode system (also two window types) Electron Tubes 9117B 11 June 2011, TIPP-2011, Chicago, USA 5 Exploit the lower AP rates of the R8619 with the high QE of the R9420 !

1.5‘ Electron Tubes Enterprises 9117B 11 June 2011, TIPP-2011, Chicago, USA Razmik Mirzoyan: Improved PMTs forthe CTA Project 6

11 June 2011, TIPP-2011, Chicago, USA Razmik Mirzoyan: Improved PMTs forthe CTA Project 1.5’ PMT Hamamatsu R9420, predecessor of the current R Simulated ph.e. angular distribution ~ cos(  ) = 400 nm Single ph.e. Development goal: improve the QE but also optimise the ph.e. Collection Efficiency The product of QE x Collection Efficiency is the Photon Detection Efficiency optimise the TTS 7

The measured QE of the 1.5´CTA target PMT from Hamamatsu 11 June 2011, TIPP-2011, Chicago, USA Razmik Mirzoyan: Improved PMTs forthe CTA Project 8

Afterpulse Rate measurements Razmik Mirzoyan: Improved PMTs forthe CTA Project Single Photoelectron measurement estimate F-factor and Gain, evaluate amplitude of pulses AP data taking: record 20 µs long FADC trace after main pulse (2 GHz sampling rate), events per HV for 5 to 30 phe pulse amplitude offline Analysis of recorded data: AP Arrival time, Pulse shapes and rates 11 June 2011, TIPP-2011, Chicago, USA 9

Single photoelectron measurement Razmik Mirzoyan: Improved PMTs forthe CTA Project 1.5 ” Hamamatsu 9420 MODP: 11 June 2011, TIPP-2011, Chicago, USA 10

Target Hamamatsu PMT operated at a HV 900 V, gain ~ 40k 11 June 2011, TIPP-2011, Chicago, USA Razmik Mirzoyan: Improved PMTs forthe CTA Project A n amplifier providing 5000e- equivalent noise/10ns (developed in Univ. Barcelona) has been used for this measurement 11

Afterpulsing Rates new and comparable old PMTs Razmik Mirzoyan: Improved PMTs forthe CTA Project 11 June 2011, TIPP-2011, Chicago, USA 12

Afterpulsing Rates Razmik Mirzoyan: Improved PMTs forthe CTA Project TypeAP Rate ≥ 4ph.e. [%] Hamamatsu 9420Old0.3 Hamamatsu 9420 MODF XA7038New0.15 Hamamatsu 8619 MODP XA7043 (Body of 9420) New0.032 Hamamatsu 8619Old ET enterprize 9142B June 2011, TIPP-2011, Chicago, USA 13

Razmik Mirzoyan: Improved PMTs forthe CTA Project Pulse shape – Timing measurement CompanyPMT serial Window -TypeMax applied HVFWHM [ns] Hamamatsu9420 ZP0753 Flat/concave, 1,5 ”1200 V2,35 Hamamatsu9420 MODF_XA7038 Flat/concave, 1,5 ”1100 V2,42 Hamamatsu8619 DV2520 Flat/concave, 1 “900 V3,10 Hamamatsu8619 MODP_XA7043 Flat/concave, 1,5 ”1100 V2,86 Electron Tubes9117B_477Hemispherical, 1,5 ”1100 V1,53 Electron Tubes9142B_10011Flat/concave,1,125”600 V3,63 11 June 2011, TIPP-2011, Chicago, USA 14

Pulse shape Razmik Mirzoyan: Improved PMTs forthe CTA Project Hamamatsu June 2011, TIPP-2011, Chicago, USA 15

Razmik Mirzoyan: Improved PMTs forthe CTA Project Electron Tubes 9117B 11 June 2011, TIPP-2011, Chicago, USA 16 Pulse shape

Razmik Mirzoyan: Improved PMTs forthe CTA Project Pulse width dependence on the applied HV Supply voltage [V] FWHM [ns] e.g. : Hamamatsu 9420 preliminary VoltageFWHM [ns] 700 3, , , , , ,35 ~82/sqrt(HV) 11 June 2011, TIPP-2011, Chicago, USA 17

Razmik Mirzoyan: Improved PMTs forthe CTA Project AP arrival time to check, what are the sources for AP inside PMT Peaks locate ions (H +,He +,2+, CH 4 + ) Exponentially decreasing in time caused by rest gases (low  ”clean” vacuum) ET tube (first picture) has very low AP with little peaks AP sources Varies for different PMTs ! 11 June 2011, TIPP-2011, Chicago, USA 18

Razmik Mirzoyan: Improved PMTs forthe CTA Project Apply different voltages to a selected PMT; intensity of the laser pulses kept constant AP rates raise with HV Ion travel time decrease Heavy ion focusing increases with HV 11 June 2011, TIPP-2011, Chicago, USA 19

Razmik Mirzoyan: Improved PMTs forthe CTA Project PMT Glowing lower left photo: seen from top Lower right photo: towel around the PMT  light emission from the side also visible top right photo: glowing seen from side Clara CCD 10 min exposure time Filter in front to suppress the 405 nm laser light High voltage, high laser intensity We checked: all these photos show a fluorescent light emission with spectrum > 700 nm 11 June 2011, TIPP-2011, Chicago, USA 20

Razmik Mirzoyan: Improved PMTs forthe CTA Project Right top: overlay of both lower photos Left bottom: simple photo of the PMT Right bottom: dark measurement (PMT Glowing) PMT Glowing 11 June 2011, TIPP-2011, Chicago, USA Optical photo Exposure in dark: PMT emits light Overlay of optical and dark exposure photos 21

Razmik Mirzoyan: Improved PMTs forthe CTA Project Summary PMT : is approaching ~35 % in peak, folded with Cherenkov:spectrum > 20% AP rate: achieved ≤ 0.05 % ≥ 4 Phe; Goal: ≤ 0.02 % (Ham.) Pulse width: ~ 2.5 – 3 ns Photo electron collection efficiency equally important as QE: optimise the PMT input window shape and curvature (both Ham. and ETE are working on it) Both Hamamatsu and ETE are on the way of developing the best ever PMTs for the CTA project 11 June 2011, TIPP-2011, Chicago, USA 22

Razmik Mirzoyan: Improved PMTs forthe CTA Project Thank you for your attention ! 11 June 2011, TIPP-2011, Chicago, USA 23