Improved PMTs for the Cherenkov Telescope Array project

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

Cherenkov Telescope Array (CTA) for Very High Energy Ground-Based -ray Astronomy • 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 Ge. V to 100 Te. V • Answer the long-standing question about the origin of cosmic rays • ~100 telescopes, 2 -arrays (in S & N) • Site search ongoing 11 June 2011, TIPP-2011, Chicago, USA Razmik Mirzoyan: Improved PMTs forthe CTA Project 2

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

Quantum Efficiency measurements Company Type QEpeak(l) <QE>Cher Hamamatsu 8619 1“ 28, 7 ± 2, 2 (390 nm) 19, 4 ± 0, 3 Hamamatsu 9420 1, 5“ 34, 6 ± 3, 1 (370 nm) 22, 9 ± 0, 4 Hamamatsu 7724 2“ 38, 9 ± 3, 3 (370 nm) 25, 7 ± 0, 4 Electron Tubes 9117 B 1, 5“ 34, 0 ± 3, 2 (360 nm) 19, 9 ± 0, 3 Electron Tubes 9142 B 1, 125“ 30, 2 ± 2, 7 (370 nm) 16, 5 ± 0, 3 11 June 2011, TIPP-2011, Chicago, USA Razmik Mirzoyan: Improved PMTs forthe CTA Project 4

1. 5’ size, super-bialkali candidate PMTs Hamamatsu R 9420 modified (convex input window shape) (mat and polished input window types) Hamamatsu R 8619 modified Body of R 9420 but used 8619 dynode system (also two window types) Electron Tubes 9117 B 11 June 2011, TIPP-2011, Chicago, USA Exploit the lower AP rates of the R 8619 with the high QE of the R 9420 ! Razmik Mirzoyan: Improved PMTs forthe CTA Project 5

1. 5‘ Electron Tubes Enterprises 9117 B 11 June 2011, TIPP-2011, Chicago, USA Razmik Mirzoyan: Improved PMTs forthe CTA Project 6

1. 5’ PMT Hamamatsu R 9420, predecessor of the current R 11920 -10 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 Simulated ph. e. angular distribution ~ cos(q) l= 400 nm Single ph. e. 11 June 2011, TIPP-2011, Chicago, USA Razmik Mirzoyan: Improved PMTs forthe CTA Project 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 • 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), 60000 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 Razmik Mirzoyan: Improved PMTs forthe CTA Project 9

Single photoelectron measurement 1. 5 ” Hamamatsu 9420 MODP: 11 June 2011, TIPP-2011, Chicago, USA Razmik Mirzoyan: Improved PMTs forthe CTA Project 10

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

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

Afterpulsing Rates Type AP Rate ≥ 4 ph. e. [%] Hamamatsu 9420 Old 0. 3 Hamamatsu 9420 MODF XA 7038 New 0. 15 Hamamatsu 8619 MODP XA 7043 New (Body of 9420) 0. 032 Hamamatsu 8619 0. 0085 Old ET enterprize 9142 B 11 June 2011, TIPP-2011, Chicago, USA 0. 005 Razmik Mirzoyan: Improved PMTs forthe CTA Project 13

Pulse shape – Timing measurement Company PMT serial Window -Type Hamamatsu 9420 ZP 0753 Flat/concave, 1, 5 ” 1200 V 2, 35 Hamamatsu 9420 MODF_XA 7038 Flat/concave, 1, 5 ” 1100 V 2, 42 Hamamatsu 8619 DV 2520 Flat/concave, 1 “ 900 V 3, 10 Hamamatsu 8619 MODP_XA 7043 Flat/concave, 1, 5 ” 1100 V 2, 86 Electron Tubes 9117 B_477 Hemispherical, 1, 5 ” 1100 V 1, 53 Electron Tubes 9142 B_10011 Flat/concave, 1, 125” 600 V 3, 63 11 June 2011, TIPP-2011, Chicago, USA Max applied HV FWHM [ns] Razmik Mirzoyan: Improved PMTs forthe CTA Project 14

Pulse shape Hamamatsu 9420 11 June 2011, TIPP-2011, Chicago, USA Razmik Mirzoyan: Improved PMTs forthe CTA Project 15

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

Pulse width dependence on the applied HV Voltage FWHM [ns] 700 3, 11 800 2, 82 900 2, 60 1000 2, 64 1100 2, 52 1200 2, 35 FWHM [ns] e. g. : Hamamatsu 9420 ~82/sqrt(HV) preliminary Supply voltage [V] 11 June 2011, TIPP-2011, Chicago, USA Razmik Mirzoyan: Improved PMTs forthe CTA Project 17

AP sources Varies for different PMTs ! • 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 11 June 2011, TIPP-2011, Chicago, USA Razmik Mirzoyan: Improved PMTs forthe CTA Project 18

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 Razmik Mirzoyan: Improved PMTs forthe CTA Project 19

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

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

Summary PMT <QE>: 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 Razmik Mirzoyan: Improved PMTs forthe CTA Project 22

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