Cherenkov Telescope Array An advanced Facility for ground-based gamma-ray Astronomy

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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
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Basic considerations
detection technique is well understood
and very mature design based on proven
technology future upgrades possible.
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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 (, , )
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The camera
Acquisition
Light concentrator and Photon detector
Readout
Funding
Mechanics
Trigger
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Photon detectors
Classical PMT
but aging low gain high voltage cost
Better QE, resolution
HEPP
Neutrino
HEPP
HPD
Air shower
SiPM
Promising but RD dark current dynamic crosstalk

Industry
Cherenkov telescopes
Air Fluorescence
HEPP
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Photon detectors
Traditional photomultipliers seem to be the most
appropriate candidates for a design study. Its 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 RD. It should assume
flexibility. The photomultiplier technology is
mature but nevertheless quite some improvements
are possible.
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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 lt 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.

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Improvements of Classical PMT
Some progress has been achieved recently
Tested by MPIK Munich
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Improvements of Classical PMT
Claims
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Wavelength shifters
Enhance the photon conversion by shifting
wavelength to more efficient bandwidth region.
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Light concentrator
Light collector reflectivity 85 Angular
cutoff corresponding to the size of the
mirror Active area coverage gt95
Needed development of light collectors with
practical enhanced reflectivity and nearly zero
dead area between pixels.
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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 (lt10) 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 Complexit
y of installation few days to full
performance Modularity - Reliability lt5
dead channel with lt10 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 - ?
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Readout technology
Mainly two proven solutions
Trigger
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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 gt 11
bits Integral non linearity lt 1 Readout
time 1.4 µs (for 16 ns signal) Crosstalk lt
3 Total noise 0.8 mV rms Maximum readout
frequency gt 400 kHz Sampling Frequency Range up
to 4 GHz Number of channels 2-10 Number of
cells 256-1024 Maximum signal amplitude gt 2 V
More sophisticated ASIC are still under study to
equip the front end part of the electronics.
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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).
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Acquisition
Two different standards are currently used in
Cherenkov technique. CompactPCI (HESS) VME
(MAGIC) With the development of dedicated
electronics cards.
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Mechanics

• Mechanics should be
• Compact
• built and fully tested in a lab before
  installation on site (few days).
• Modularity
• lt5 dead channel with lt10 person days maintenance
  per year.
• Adapt new technology and photon detectors
• Low weight
• Cheap

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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.
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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)
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LOI
ETC
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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 RD is for the cost.

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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