Advanced Cherenkov Telescope Array Development for High-Energy Physics Research

1. Cherenkov Telescope Array Robert Bazer-Bachi Stella Bradbury Osvaldo Catalano Gerard Fontaine Florian Goebel Philippe Goret German Hermann Eckart Lorenz Manel Martinez Razmik Mirzoyan Jelena Ninkovic Nepomuk Otte Riccardo Paoletti Bernard Peyaud Michael Punch Joachim Rose Thomas Schweizer Jean-Paul Tavernet Masahiro Teshima Nicola Turini Pascal Vincent Camera and electronics Manel Martinez and Pascal Vincent on behalf of the Camera Working Group

2. Basic considerations “… detection technique is well understood and very mature …” “… design based on proven technology … … future upgrades possible.”

3. Layout 30-50 telescopes 10000 m2 mirror area 50 m2 photo sensitive area 50k-100k electronics channels Possibly mix of telescopes (5m, 14m, 28m) with only factor of 10 in € ($, £, ¥ …)

4. Thecamera Acquisition Light concentrator and Photon detector Readout Funding Mechanics Trigger

5. Photon detectors Classical PMT but aging low gain high voltage … cost Better QE, resolution … HEPP Neutrino HEPP HPD Air shower SiPM Promising but R&D dark current dynamic crosstalk … Industry Cherenkov telescopes Air Fluorescence HEPP

6. Photon detectors Traditional photomultipliers seem to be the most appropriate candidates for a design study. It’s a mature technology at low cost. But the design of future cameras (electronics and mechanics) should take into account the possible success in new photon detector R&D. It should assume flexibility. The photomultiplier technology is mature but nevertheless quite some improvements are possible.

7. PhotoMultiplier Tubes • Improvements of Classical PMT • Higher QE alkaline photo cathodes. • Reduction of after pulses. • Improved electron optics in the PMT (photoelectron collection efficiency, uniform gain over the first dynode and very small transit time spread). • d) Better separation of single photoelectron from system noise. • Operation at lower gain (2-5x103) by a low number of dynodes in order to cope with high background light levels and to reduce aging effects (operate during partial moonshine). High quality preamps to compensate for the low gain of few dynode PMT • Dynode structures to conserve very narrow pulse structures (pulses with < 1 nanosecond FWHM) • Compact geometry with hemispherical cathodes • Lowering of the necessary HV for a fixed gain (by increasing the gain/dynode) and use of low power consumption HT units nevertheless able to provide reasonably high peak pulses. • Smart HV controllers to protect automatically against adverse high level light background • Integration of peripheral electronics (HV, divider, preamp) to compact units of low power in order to decrease the camera power and the needed cooling power and zero background emission causing EMI on neighboring elements • Improvement of peripheral increase of the QE by means of scattering lacquer coatings or other means of cathode window surface treatment to enhance the chance of multiple photon passage of semitransparent photo cathodes. • Making secondary surfaces highly reflective in the front-end area • Minimization of backscatter losses of the first dynode. • …

8. 2’’ 3’’ 2’’ Improvements of Classical PMT Some progress has been achieved recently Tested by MPIK Munich

9. Improvements of Classical PMT Claims

10. Wavelengthshifters Enhance the photon conversion by shifting wavelength to more efficient bandwidth region.

11. Light concentrator Light collector reflectivity 85 % Angular cutoff corresponding to the size of the mirror Active area coverage >95% Needed : development of light collectors with practical enhanced reflectivity and nearly zero dead area between pixels.

12. Electronics Assuming 50k-100k channels readout electronics: Pulse shape information readout window, time of signal arrival, amplitude/charge of the signal Digitization number bits does match 5 000 photo-electron dynamic range Single photo-electron resolution peak/valley ≥ 1.5 Dead time at 10 kHz few % (<10%) Input band width bigger than the pulse shape frequency Sampling rate to be define with MC and measurement ? Crosstalk no Electronic noises much less than the single photo-electron Electronic power consumption = 3.1 W/channel Programmable trigger Environmental robustness yes Stability of operation signal calibrated at 2% Temperature stability Complexity of installation few days to full performance Modularity - Reliability <5% dead channel with <10 person days maintenance per year Mass production Reproducibility Manpower for characterization and monitoring less than 2 persons €/channel (from PM to net) 500 – 1 000 € / channel +- ? …

13. GHz sampling analog memory ADC FIFO 256-1024 ns memory depth Flash ADC Digital memory μs … ms memory depth Readout technology Mainly two proven solutions : Trigger

14. Readout technology New electronics components, specially dedicated to Cherenkov technique, are now developed and produced. SAM (HESS II) Domino (MAGIC II) Power consumption 300-35 mW Analogue bandwidth 250-300 MHz Dynamic range > 11 bits Integral non linearity < 1% Readout time 1.4 μs (for 16 ns signal) Crosstalk < 3‰ Total noise 0.8 mV rms Maximum readout frequency > 400 kHz Sampling Frequency Range up to 4 GHz Number of channels 2-10 Number of cells 256-1024 Maximum signal amplitude > 2 V More sophisticated ASIC are still under study to equip the front end part of the electronics.

15. Trigger Different strategies have been developed Sectors (HESS I) Cluster (MAGIC) first Neighbors second Neighbors Sector + Neighboring (HESS II) based on usage of comparator (HESS) or discriminator (MAGIC/SPC) for the treatment of the analogue signal. Simulations needed to define the most appropriated strategy. Also dedicated chip has been developed for L1 and L2 triggering (HESS II).

16. Acquisition Two different standards are currently used in Cherenkov technique. CompactPCI (HESS) VME (MAGIC) With the development of dedicated electronics cards.

17. Mechanics • Mechanics should be : • Compact • built and fully tested in a lab before installation on site (few days). • Modularity • <5% dead channel with <10 person days maintenance per year. • Adapt new technology and photon detectors • Low weight • Cheap

18. Mechanics • Embedded camera with fully integrated electronics has advantages : • allows full construction and test in laboratory • local treatment faster with integrated electronics • and minimize the signal distortion • allows a complete monitoring and slow control of the system • limit the number of connections • facilitates the installation and maintenance • For light carbon structure telescopes new • materials can be studied to reduce weight. • With camera unload facility one can imagine • to have spare camera to allow regular maintenance.

19. Cost For a system of : 50 m2 photo sensitive area 50k-100k electronics channels Cost per channel should be of the order of 500 €, well above what we do. We can imagine 1 k€ for some units for more sophisticated data (pulse shape, timing information …). Homogenous system or few design made from the same building block Mass production Construction shared by many laboratories (opposite to Airbus)

20. LOI ETC

21. Conclusions • Optimization of design is needed: • Improvement of photomultiplier tubes (+ wavelength shifters). Light concentrators with better transmission. In parallel we may keep an eye on new photon detector. • Electronics : • Development of new ASIC to integrate readout (analogue memories + ADC + data buffering + …). • Dedicated chip for trigger or other purpose. • Define standard for acquisition design • Study of new materials for the mechanics • Simulations (light collection, trigger, resolution …) • These studies could be achieved in a 2-3 years program. • The only R&D is for the cost.

22. Cherenkov Telescope Array Thank you Robert Bazer-Bachi, Stella Bradbury, Osvaldo Catalano, Gerard Fontaine, Florian Goebel, Philippe Goret, German Hermann, Eckart Lorenz, Manel Martinez, Razmik Mirzoyan, Jelena Ninkovic, Nepomuk Otte, Riccardo Paoletti, Bernard Peyaud, Michael Punch, Joachim Rose, Thomas Schweizer, Jean-Paul Tavernet, Masahiro Teshima, Nicola Turini, Pascal Vincent