Enhanced Photomultiplier Tubes for Cherenkov Telescope Array Project

1. 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

2. 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 GeVto 100 TeV • Answer the long-standing question about the origin of cosmic rays • ~100 telescopes, 2-arrays (in S & N) • Site search ongoing Razmik Mirzoyan: Improved PMTs forthe CTA Project

3. Cherenkov Telescope Array (CTA) • 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) Razmik Mirzoyan: Improved PMTs forthe CTA Project

4. Quantum Efficiency measurements Razmik Mirzoyan: Improved PMTs forthe CTA Project

5. 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) Exploit the lower AP rates of the R8619 with the high QE of the R9420 ! Electron Tubes 9117B Razmik Mirzoyan: Improved PMTs forthe CTA Project

6. 1.5‘ Electron Tubes Enterprises 9117B Razmik Mirzoyan: Improved PMTs forthe CTA Project

7. 1.5’ PMT Hamamatsu R9420, predecessor of the current R11920-100-10 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) • = 400 nm Single ph.e. Razmik Mirzoyan: Improved PMTs forthe CTA Project

8. The measured QE of the 1.5´CTA target PMT from Hamamatsu Razmik Mirzoyan: Improved PMTs forthe CTA Project

9. 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 Razmik Mirzoyan: Improved PMTs forthe CTA Project

10. Single photoelectron measurement 1.5 ” Hamamatsu 9420 MODP: Razmik Mirzoyan: Improved PMTs forthe CTA Project

11. 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 Razmik Mirzoyan: Improved PMTs forthe CTA Project

12. Afterpulsing Rates new and comparable old PMTs Razmik Mirzoyan: Improved PMTs forthe CTA Project

13. Afterpulsing Rates Razmik Mirzoyan: Improved PMTs forthe CTA Project

14. Pulse shape – Timing measurement Razmik Mirzoyan: Improved PMTs forthe CTA Project

15. Pulse shape Hamamatsu 9420 Razmik Mirzoyan: Improved PMTs forthe CTA Project

16. Pulse shape Electron Tubes 9117B Razmik Mirzoyan: Improved PMTs forthe CTA Project

17. Pulse width dependence on the applied HV e.g. : Hamamatsu 9420 FWHM [ns] ~82/sqrt(HV) preliminary Supply voltage [V] Razmik Mirzoyan: Improved PMTs forthe CTA Project

18. 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+, CH4+) • Exponentially decreasing in time • caused by rest gases (low”clean” vacuum) • ET tube (first picture) has very low AP • with little peaks Razmik Mirzoyan: Improved PMTs forthe CTA Project

19. 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 Razmik Mirzoyan: Improved PMTs forthe CTA Project

20. 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 Razmik Mirzoyan: Improved PMTs forthe CTA Project

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

22. 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 Razmik Mirzoyan: Improved PMTs forthe CTA Project

23. Thank you for your attention ! Razmik Mirzoyan: Improved PMTs forthe CTA Project