Improved PMTs for the Cherenkov Telescope Array project Razmik Mirzoyan

Improved PMTs for the Cherenkov Telescope Array project

Razmik Mirzoyanfor the Focal Plane Instrumentation WG

Max-Planck-Institute for PhysicsMunich, Germany

Razmik Mirzoyan: Improved PMTs forthe CTA Project11 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 2Razmik 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

Company Type QEpeak() <QE>Cher

Hamamatsu 86191“

28,7 ± 2,2 (390 nm)

19,4 ± 0,3

Hamamatsu 94201,5“

34,6 ± 3,1 (370 nm)

22,9 ± 0,4

Hamamatsu 77242“

38,9 ± 3,3 (370 nm)

25,7 ± 0,4

Electron Tubes

9117B1,5“

34,0 ± 3,2 (360 nm)

19,9 ± 0,3

Electron Tubes

9142B1,125“

30,2 ± 2,7 (370 nm)

16,5 ± 0,3

11 June 2011, TIPP-2011, Chicago, USA 4


1.5’ size, super-bialkali candidate PMTs

Hamamatsu R9420 modified(convex input window shape)(mat and polished input window types)

Hamamatsu R8619 modifiedBody of R9420 but used 8619 dynode system (also two window types)

Electron Tubes 9117B


Exploit the lower AP rates of the R8619 with the high QE of the R9420 !

1.5‘ Electron Tubes Enterprises 9117B





1.5’ PMT Hamamatsu R9420, predecessor of the current R11920-100-10

Simulated ph.e. angular distribution~ cos()= 400 nmSingle ph.e.

Development goal: improve the QE but also optimise the ph.e. Collection EfficiencyThe product of QE x Collection Efficiency is the Photon Detection Efficiency optimise the TTS

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The measured QE of the 1.5´CTA target PMT from Hamamatsu



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


Single photoelectron measurement


1.5 ” Hamamatsu 9420 MODP:


Target Hamamatsu PMT operated at a HV 900 V, gain ~ 40k



A n amplifier providing 5000e- equivalent noise/10ns (developed in Univ. Barcelona) has been used for this measurement

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Afterpulsing Rates new and comparable old PMTs

Razmik Mirzoyan: Improved PMTs forthe CTA Project11 June 2011, TIPP-2011, Chicago, USA 12

Afterpulsing Rates


Type AP Rate ≥ 4ph.e. [%]

Hamamatsu 9420 Old 0.3

Hamamatsu 9420 MODF XA7038 New 0.15

Hamamatsu 8619 MODP XA7043(Body of 9420)

New 0.032

Hamamatsu 8619 Old 0.0085

ET enterprize 9142B 0.005



Pulse shape – Timing measurementCompany PMT

serialWindow -Type Max applied HV FWHM [ns]

Hamamatsu 9420ZP0753

Flat/concave, 1,5 ” 1200 V 2,35

Hamamatsu 9420MODF_XA7038

Flat/concave, 1,5 ” 1100 V 2,42

Hamamatsu 8619DV2520

Flat/concave, 1 “ 900 V 3,10

Hamamatsu 8619MODP_XA7043

Flat/concave, 1,5 ” 1100 V 2,86

Electron Tubes 9117B_477 Hemispherical, 1,5 ” 1100 V 1,53

Electron Tubes 9142B_10011 Flat/concave,1,125” 600 V 3,63


Pulse shape


Hamamatsu 9420



Electron Tubes 9117B


Pulse shape


Pulse width dependence on the applied HV

Supply voltage [V]

2,00

2,20

2,40

2,60

2,80

3,00

3,20

600 800 1000 1200

e.g. : Hamamatsu 9420

preliminary

Voltage FWHM [ns]

700 3,11

800 2,82

900 2,60

1000 2,64

1100 2,52

1200 2,35

~82/sqrt(HV)



• AP arrival time to check, what are the sources for AP inside PMT• Peaks locate ions (H+,He+,2+, CH4

+)• Exponentially decreasing in time caused by rest gases (low”clean” vacuum)• ET tube (first picture) has very low AP with little peaks

AP sourcesVaries for different PMTs !



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



PMT Glowing

lower left photo: seen from topLower 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 timeFilter in front to suppress the 405 nm laser lightHigh voltage, high laser intensity

We checked: all these photos show a fluorescent light emission with spectrum > 700 nm



Right top: overlay of both lower photosLeft bottom: simple photo of the PMTRight bottom: dark measurement (PMT Glowing)

PMT Glowing


Optical photo Exposure in dark: PMT emits light

Overlay of optical and dark exposure photos

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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 (bothHam. and ETE are working on it)• Both Hamamatsu and ETE are on the way of developing the best ever PMTs for the CTA project



Thank you for your attention !


Improved PMTs for the Cherenkov Telescope Array project Razmik Mirzoyan

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