FACT First GAPD Cherenkov TelescopeLHC Days in Split
4-9 October 2010, Split, CroatiaW. Lustermann, ETH Zurich on behalf of the FACT collaboration
•TU Dortmund, Dortmund, Germany•ISDC, Geneva, Switzerland•EPFL, Lausanne, Switzerland•University of Würzburg, Würzburg, Germany•ETH, Zurich, Switzerland
Collaboration
•Introduction•Catching the photons•Mechanics / Electronics•Summary / Outlook
Content
LHC Days, Split, 4-9 Oct, 2010 2W. Lustermann
Detection of Air Cherenkov Showers
Cherenkov spectrum 2.2 km altitude Cut off ~320 nm
Signal amplitude: 200 photons / m2 (1 TeV γ-ray)Spectrum: (300 – 600) nmDuration: few nsNight sky: up to several GHz
Optical imaging system (causes losses)Mirror light concentrators photo-detectors
LHC Days, Split, 4-9 Oct, 2010 3W. Lustermann
FACT Project
FACT instrument: Hegra CT3 Telescope, La Palma• Owner: MPI for Physics, Munich• Location: European Northern Observatory, Roque de los
Muchachos, Canary Island La Palma• altitude: 2199.4 m, longitude: -17deg 53m 26s, latitude:
28deg 45m 42s • Close to the MAGIC telescopes
Mirror Dish• Number of mirrors: 30• Mirror arrangement: 1 ring of 6 and two rings of 12
mirrors, no central mirror (camera shadow)• Diameter: 3.885 m• total mirror surface: 9.51 m2
• Surface coverage: 82.9 % (not counting the missing central mirror)
FACT project objectives• Construction of the first imaging air -
shower Cherenkov telescope using G-APDs (Geiger mode avalanche photo diodes) as photo-detectors
• gain operation experience (including Crab-nebula observation)
Former HEGRA CT3 telescopeLa Palma, Canary Islands
Two new technologies for IACTs• G-APDs as photo-detectors• Solid light concentrators
LHC Days, Split, 4-9 Oct, 2010 4W. Lustermann
Mirrors (re-use existing Hegra CT1 mirrors) • Spherical mirrors with hexagonal shape• Diameter (inner circle): 60.6cm• area: 0.317 m2
Sandwich construction:• Al base plate, 1 mm thick• Al honeycomb (hexcell)• Al alloy (AlMgSi 0.5) front plate, 5 mm thick• Weight: ~6 kg
Surfaces were re-machined• diamond milling by LT ultra Precision Technology GmbH• Mean focal length: (4.890 ± 0.008) m• Average spot size at 2f: 16.0 mm2 (0.033 deg)
Surface finish• Sputtering of Silicon in a Methan-atmosphere followed by oxidation• Fraunhofer-Institut für Fertigungstechnik und Angewandte Materialforschung – IFAM (Bremen)• thickness: ~120 nm• reflectivity maximum around 450 nm, average reflectivity of ~90% between (300 and 500) nm
Mirrors
LHC Days, Split, 4-9 Oct, 2010 5W. Lustermann
Light Concentrator (Winston Cones)Height: 19.939 mmIN: Hexagon: 9.5 mmOUT: Square: 2.8 mmConcentration: 7.48Solid cones use total internal reflection
Light Concentrating Cones
• UV transparent PMMA• normal parabolas shape
• Fabricated by injection moulding (IMOS Gubela GmbH)
• Presently prototypes are tested
Angular acceptance
• Cutoff angle 20 deg• observe only the mirror,
reduces night sky background
simulation
Data sheet of raw material for injection molding:Cut off ~320 nm
Thanks for the support of University of Zurich.
- ideal cone- realistic cone
LHC Days, Split, 4-9 Oct, 2010 6W. Lustermann
Light Concentrator (Winston Cones)Simulation
• Input Cherenkov spectrum• Fresnel reflection losses
• Transparency (λ)• Surface roughness
• G-APD angular acceptance• G-APD spectral response (λ)
Output light distribution (simulation)IMOS using ZEMAX ray tracing program
Output light distribution (simulation FACT) We can trust our simulation
Distribution of exit anglesImportant for photo-
detectors
simulation- ideal cone- realistic cone
LHC Days, Split, 4-9 Oct, 2010 7W. Lustermann
Photo Detectors (G-APDs)Photo detectors: MPPC
Manufacturer: Hamamatsu Photonics K.K.
Type: S10362-33-050C• active area: 3 x 3 mm2
• 3600 pixels of (50 m)2
• Ceramic package 5.9 x 6.6 mm2
Operation voltage: ~70 V
Gain (nominal): 7.5 x 105
Photon detection efficiency: ~35%
Optical cross talk and after pulsing: ~25%
Peak sensitivity ~430 nm
T dependence of Vb: -60 mV/K
LHC Days, Split, 4-9 Oct, 2010 8W. Lustermann
Photo Detection (Cone + GAPD)
Observed spectrum based on simulation, measured Cherenkov light spectrum, G-APD and cone properties
HeNe laser light injection
image measured
Input Cherenkov spectrum folded with G-APD acceptance- ideal cone
- realistic cone
- 80.7 %- 75.6 %
efficiency
LHC Days, Split, 4-9 Oct, 2010 9W. Lustermann
Camera Mechanics
LHC Days, Split, 4-9 Oct, 2010 10W. Lustermann
FACT Camera and Telescope
Camera• PMMA 7M entrance window,
transmission > 82% for > 300 nm• Solid light concentrators (Winston-
cones)• 1440 pixels (G-APDs)• FOV: 0.11 deg / pixel (4.5 deg total)
Design requirements• Dynamic range: 333 photons / pixel• Resolution: 0.5 photons (for less than 10 photons)• Timing resolution: 300 ps• Double hit resolution: 5 ns• Operation also under twilight/moon (background
rate up to 1 GHz / pixel)
Infrastructure (power, Ethernet, counting hut, …)
Cooling system Internal light pulser
External light pulser (bias
supply feedback)
G-APD bias supplies
Telescope Drive system
Camera mechanics
including Shutter
Signal conditioning &
DAQ system
Online monitoring and control software
Simulation and analysis software
Drive calibration system
Temperature and Humidity
monitoringTrigger system LV power supplies
Money, optimism and very good
people
LHC Days, Split, 4-9 Oct, 2010 11W. Lustermann
Camera Mechanics
Length 812 mm, diameter 532 mm, weight approx. 100 kg
4 water cooled electronic crates
Sensor and electronics compartment thermally separated
The construction must be water tight (following IP67) specifications:This concerns the housing as well as connectors on the patch panel
Crates
Sensorcompartment
Connectors
Ethernet switches
Window
Mount to telescopeShutter
LHC Days, Split, 4-9 Oct, 2010 12W. Lustermann
Sensor Compartment Details
Co-axial signal cables, 50 ohm, ~35 cm
G-APDs withWinston cones
Cable adapters /bias feed
Front baffle plate
2 x GAPD bias
9 G-APDstrigger patch
LHC Days, Split, 4-9 Oct, 2010 13W. Lustermann
Electronics Systems Overview
FLV: low voltage conversionFSC slow control (Temp., rel Humidity, voltages)FLP light pulserFDC drive calibration
2 GHz
LHC Days, Split, 4-9 Oct, 2010 14W. Lustermann
Single Photon Spectrum
0 2 4 6 8 10 12 14200
300
400
500
600
700
800
900 Linearity (area mea-surement)
number of photons (peak)
peak
pos
ition
(mea
n ch
arge
)
Measured Spectrum using
• MPPC• FACT pre-amplifier (FPA)• oscilloscope
LHC Days, Split, 4-9 Oct, 2010 15W. Lustermann
FACT DAQ – LED pulses
Pre-amplifier board (FPA) and analog pipeline (DRS4) & digitization board (FAD) connected via the mid plane (FMP) distributing power and slow control signals
LED flashes registered by an MPPC connected to the FACT readout system
2 GHz500 ns
LHC Days, Split, 4-9 Oct, 2010 16W. Lustermann
Trigger system & HV FeedbackTrigger unit (FTU) – 40 pieces• Uses 4 sums of 9 pixels for a
majority decision• Mezzanine card on the FPA
Trigger master (FTM) – 1 piece• Provides trigger decision upon 40 FTU inputs• Provides CLOCK, TRIGGER and RESET signals
32 channel GAPD bias card• Computer
controlled (USB)
• Counting hut
Active bias supply feedback• Light pulses of 9 LEDs (FLP) are triggered by
the FTM and read out• Deviations from nominal values are converted
into GAPD bias corrections and applied.
Feedback OFF
Feedback ON
Measured light pulse response
LHC Days, Split, 4-9 Oct, 2010 17W. Lustermann
GAPD bias supply system
Single channel board• HV operational amplifier OPA454• controlled by a 12 bit serial DAC
(DA8034U)• output voltage adjustable (0 – 90) V• calibration using trim potentiometer• voltage set precision 22 mV• High side current monitor (HV7800)• Over current protection, limit (1-
5)mA
32 channel HV mother boards
HV crate: 320 channels• 1 crate controller with USB interface• 10 HV mother boards• power conversion /distribution and control
bus wired in the back of the crate
LHC Days, Split, 4-9 Oct, 2010 18W. Lustermann
First MeasurementsNight of 2.-3. June on the roof of ETH physics building
Mirror• 80 cm focal length• FOV: 1 deg /pixel
NSB• from buildings and
moonlight:• 1.2 GHz / pixel
PA48
SP16 CP144
LHC Days, Split, 4-9 Oct, 2010 19W. Lustermann
Event 21 Run 201
• 25mV single pixel threshold (4 p.e.)
• Majority 4 out of 16• 100 kHz trigger rate per
pixel• 0.1 Hz total rate• 2 GHz sampl. freq.
Horizontal: 0 ... 512 ns, Vertical: -50 ... 850mV
LHC Days, Split, 4-9 Oct, 2010 20W. Lustermann
Summary / Outlook
•Mirrors and drive system ready for installation•Installation in Oct. 2010
Telescope
•Design including cooling finalized•Fabrication of components started
Mechanics•all G-APDs available•Winston cone fabrication ongoingPhoto Detection
•Fully integrated into the camera•Prototypes tested, series production ongoing
Electronics
•Fabrication of all components in 2010•Integration + installation + observations 2011
Perspektives
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