nec2013 – xxv international symposium on nuclear electronics and computing 9-16 sept 2013, varna,...
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FACT - First GAPD imaging air shower Cherenkov Telescope – electronics systems
NEC2013 – XXV International Symposium on Nuclear Electronics and Computing 9-16 Sept 2013, Varna, Bulgaria
W. Lustermann, ETH Zurich for the FACT collaboration
TU Dortmund, ISDC Geneva, University of Geneva, EPFL Lausanne, University of Würzburg, ETH Zurich
• Introduction• Camera systems• Electronics• Control software• Results• Summary/Conclusion
Content
NEC2013, 8-16 Sept 2013, Varna, Bulgaria 2W. Lustermann, ETH Zurich (for the FACT collaboration)
Detection > 100 GeV gamma rays
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
Showers can as well originate from protons or electrons – requires a selection
NEC2013, 8-16 Sept 2013, Varna, Bulgaria 3W. Lustermann, ETH Zurich (for the FACT collaboration)
Gamma induced air shower detectionGOAL: detection of gamma induced air showers, measurement of the energy and the source position at the sky
The image parameters including the shower shape, position, photon arrive times allow the reconstruction of energy and source position- Air showers induced by gammas, muons and electrons are short ~few ns- Air showers induced by protons are rather long ~(30 – 100) nsThe lower the detectable light level the lower the energy threshold for photons
Operation at high night sky background (~1GHz) and at moon light conditions, should be possible – extending observation time
NEC2013, 8-16 Sept 2013, Varna, Bulgaria 4W. Lustermann, ETH Zurich (for the FACT collaboration)
The TelescopeRefurbished HEGRA CT3• Mirror area: 9.5 m2
• New drive system• New counting hut and
electrical installation
European Northern Observatory• Roque de los Muchachos, altitude: 2200 m• Canary Island La Palma
New camera• G-APDs (SiPMs. …)• Solid light guides• Fully integrated
electronics• Using DRS4
Operational since October 2011• Monitoring of bright
Blazars• Evaluation of stability
and performance
NEC2013, 8-16 Sept 2013, Varna, Bulgaria 5W. Lustermann, ETH Zurich (for the FACT collaboration)
Camera features/requirements
Camera• Dim: Length 812 mm, diameter 532 mm,• Weight: ~ 150 kg• 1440 pixels (G-APDs)• FOV: 0.11 deg / pixel (4.5 deg total)• Water cooled
4.5
deg
Requirements for the readout electronics:• Dynamic range: ~200 photons / pixel• Resolution: < 0.5 photons (for less than 10
photons) – this will allow to measure the gain of the GAPDs from single photon spectra
• Timing resolution ~500 ps• Typical trigger rate of ~50 Hz (~ 350 Hz
sustainable trigger rate)• Synchronous trigger distribution ~50ps • Low power consumption
additional electronics:• G-APD bias supply• Low voltage power
conversion system• Light monitoring system• Slow control system
NEC2013, 8-16 Sept 2013, Varna, Bulgaria 6W. Lustermann, ETH Zurich (for the FACT collaboration)
Telescope Systems Overview
NEC2013, 8-16 Sept 2013, Varna, Bulgaria 7W. Lustermann, ETH Zurich (for the FACT collaboration)
Electronics Systems Overview
FLV: low voltage conversionFSC slow control (Temp., rel Humidity, voltages)FLP light pulserFDC drive calibration
2 GHz
NEC2013, 8-16 Sept 2013, Varna, Bulgaria 8W. Lustermann, ETH Zurich (for the FACT collaboration)
Photo Detectors (G-APDs)
Photo detectors: Hamamatsu MPPC• active area: 3 x 3 mm2
• 3600 pixels of (50 m)2
Operation voltage: ~70 V
Gain (nominal): 7.5 x 105
Photon detection efficiency (peak): ~35%
Single photon resolution
• Easy to use• As good as best PMTs (PDE)• Cheaper than PMTs• Dark counts, cross talk and after pulse are
no problem for IACTs• Voltage and Temperature dependence can
be kept under control rather easily
MPPC glued to solid light concentrator:Increase of the sensitive areaLimiting angular (watch only the mirror)
NEC2013, 8-16 Sept 2013, Varna, Bulgaria 9W. Lustermann, ETH Zurich (for the FACT collaboration)
Electronics Systems Overview
FLV: low voltage conversionFSC slow control (Temp., rel Humidity, voltages)FLP light pulserFDC drive calibration
2 GHz
NEC2013, 8-16 Sept 2013, Varna, Bulgaria 10W. Lustermann, ETH Zurich (for the FACT collaboration)
FACT Pre-Amplifier (FPA)
Pre-amplifier• 36 pre-amplifiers channels • Input: AC coupling with npn transistor in base configuration• Input impedance: 25 ohm• Followed by an OPA with gain ~10• gain: 45 mV / µA• Bandwidth: 200 MHz• Single avalanche signal 2.5 mV at the FAD input of 50 ohm
Two different functionalities:• Pre-amplification of signals for later digitization• Summing of signals for the trigger primitives generation
design: U. Roeser, layout: L.Djambazov
NEC2013, 8-16 Sept 2013, Varna, Bulgaria 11W. Lustermann, ETH Zurich (for the FACT collaboration)
Electronics Systems Overview
FLV: low voltage conversionFSC slow control (Temp., rel Humidity, voltages)FLP light pulserFDC drive calibration
2 GHz
NEC2013, 8-16 Sept 2013, Varna, Bulgaria 12W. Lustermann, ETH Zurich (for the FACT collaboration)
FACT Digitization (FAD)DRS4 (Domino Ring Sampler) – PSI (S. Ritt)- Analog switched capacitor array- 9 channels, 1024 time slices per channel- Operated at 2 GHz (500ps / slice)- ROI: 300 slices (150 ns)- Serial readout- Digitization 12 bit ADC running at 20 MHz
FAD board (in total 40)- 36 channels, four DRS4 with input buffers- 2 dual 12bit ADC (AD9238)- Ethernet interface (Wiznet W5300)- FPGA (Xilinx Spartan-3)- Internal PLL of DRS4 used, locked on clock of
the trigger master- Relative timing of all channels of all boards to
300ps is possible (requires calibration)- Controllable voltage source for amplitude
calibration
DRS4 data: permit and require digital signal processing
NEC2013, 8-16 Sept 2013, Varna, Bulgaria 13W. Lustermann, ETH Zurich (for the FACT collaboration)
Arrangement of PCBs
Pre-amplifier board (FPA) and analog pipeline ASIC (DRS4) & digitization board (FAD) connected via the mid plane (FMP) distributing power and slow control signals
4 water cooled costume crates:• 10 FAD boards• 10 FPA + FTU boards• Heat spreading planes in the pcb’s• Wedge locks as thermal interface
Mid plane (FMP): • press fit connectors with pins mate able on both side for
analog signal passage• RS485 buses• Power distribution
FAD’s in one crate are booted in sequence: limit the startup power (required for FPGA booting)
FTU
FPA
FAD
FMP
FPA
FMP
FAD
NEC2013, 8-16 Sept 2013, Varna, Bulgaria 14W. Lustermann, ETH Zurich (for the FACT collaboration)
Electronics Systems Overview
FLV: low voltage conversionFSC slow control (Temp., rel Humidity, voltages)FLP light pulserFDC drive calibration
2 GHz
NEC2013, 8-16 Sept 2013, Varna, Bulgaria 15W. Lustermann, ETH Zurich (for the FACT collaboration)
Trigger system (1)
Trigger unit (FTU) – 40 pieces• Mezzanine card on the pre-amplifier card• 12 bit DACs for discriminators thresholds: 15 DAC counts / p.e.• Majority coincidence N-out-of-4 logic, combine trigger signals
(practically an OR is used)• RS485 interface to trigger master
FPA: pre-amplifier• analog summing of signals of patches (9 channels)• Masking of individual channels (noisy)• Clipping of trigger sum to 10 ns• Discrimination of the sums: 4 trigger signals
• Trigger on analog sums of non overlapping patches: 9 pixel• Functionality spread over several components: FPA – pre-
amplifier, FTU – trigger unit and FTM – trigger master• Rate control system (software) maintains a constant trigger
rate (70 Hz) under varying conditions
Counter for all discriminator outputs and the majority coincidence output are implemented automatic adjustment of discriminator thresholds stabilize trigger rates under varying conditions
NEC2013, 8-16 Sept 2013, Varna, Bulgaria 16W. Lustermann, ETH Zurich (for the FACT collaboration)
Electronics Systems Overview
FLV: low voltage conversionFSC slow control (Temp., rel Humidity, voltages)FLP light pulserFDC drive calibration
2 GHz
NEC2013, 8-16 Sept 2013, Varna, Bulgaria 17W. Lustermann, ETH Zurich (for the FACT collaboration)
Trigger system – Trigger master
Trigger master (FTM) – 1 piece• receives 40 FTU signals• Trigger: N out of 40 logic, for an
adjustable time window of (8-64)ns• Special triggers: light pulser (N=25)
random (clock)• Interface for external trigger• Triggers can be individually enabled
and run simultaneously • Ethernet interface for control and
setup• Control of all sub units FAD and FTU
via RS485
Note: the trigger part of the VHDL code was purchased from a company
NEC2013, 8-16 Sept 2013, Varna, Bulgaria 18W. Lustermann, ETH Zurich (for the FACT collaboration)
Electronics Systems Overview
FLV: low voltage conversionFSC slow control (Temp., rel Humidity, voltages)FLP light pulserFDC drive calibration
2 GHz
NEC2013, 8-16 Sept 2013, Varna, Bulgaria 19W. Lustermann, ETH Zurich (for the FACT collaboration)
FTM continued and fast control (FFC)4 fast control signals: CLOCK, RESET, TRIGGER, TIMEMARKER
• CLOCK: used to synchronize all DRS4 (<100ps jitter)• RESET: reset all DRS4• Trigger:
• upon detection of a trigger condition a rectangular pulse (TIMEMARKER) is emitted (with a customizable delay) which is coupled into channel 9 of all DRS4 chips
• After another customizable delay the TRIGGER signal is send• A bit pattern containing the event ID and the trigger type is distributed to all FAD boards via
RS485 and included into the digitized data• While digitizing the FAD boards send a busy signal blocking the generation new triggers
Tow dedicated fast control pcbs: • 1 to 10 fold fan-outs (ON Semiconductor
MC100LVEP111• WireWin Cat. 6 slim LVDS cables with RJ45
connectors• Test results: jitter < 20ps and skew<250 ps
NEC2013, 8-16 Sept 2013, Varna, Bulgaria 20W. Lustermann, ETH Zurich (for the FACT collaboration)
Power conversion system
three Agilent AC-DC supplies: • G-APD bias (85V) • interlock system and heaters (24V)• Camera (48V)• two 45m long cables provide power and ten
G-APD bias voltages to the patch panel
Power conversion inside the camera:• DC-DC converters (VICOR VI-J300 series)• Adapted filter: mainly a common mode choke
and a Tantalum capacitor• step-down converters on the FAD
Power consumption:• Total inside 570W• 100W in the cables• 100W DC-DC converter• Outside: 100W G-APD bias
NEC2013, 8-16 Sept 2013, Varna, Bulgaria 21W. Lustermann, ETH Zurich (for the FACT collaboration)
Slow Control
The slow control board measures:• all Voltages and currents of the DC-
DC converters• 31 temperatures close to the G-APDs
in the sensor plane• 24 temperatures for the electronics
compartment (crates, DC-DC conv.)• 4 times humidity
Slow control board:• Atmel ATmega32L micro-controller (on Arduino board)• Wiznet W5300 Ethernet interface for data transmission. • 148 channels multiplexed onto a 24 bit ADC, AD7719 with integrated
current sourcing for temperature probes.
Temperature probes: PT1000
Arduino
NEC2013, 8-16 Sept 2013, Varna, Bulgaria 22W. Lustermann, ETH Zurich (for the FACT collaboration)
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• primary power source: Agilent N5769A
G-APDs are sorted in groups of 4/5 according to their operation voltage 320 bias channels
NEC2013, 8-16 Sept 2013, Varna, Bulgaria 23W. Lustermann, ETH Zurich (for the FACT collaboration)
Sensor Plane Assembly1) MPPCs – cone gluing
2) cone gluing to front window
Completed sensor plane 3) connector cable soldering to MPPC
NEC2013, 8-16 Sept 2013, Varna, Bulgaria 24W. Lustermann, ETH Zurich (for the FACT collaboration)
Images
NEC2013, 8-16 Sept 2013, Varna, Bulgaria 25W. Lustermann, ETH Zurich (for the FACT collaboration)
Control Software (C++, boost)
DIM: Distributed Information Management System (CERN)
Qt4
NEC2013, 8-16 Sept 2013, Varna, Bulgaria 26W. Lustermann, ETH Zurich (for the FACT collaboration)
Single Photons, Time Resolution
single photon spectrum of one channel
Timing resolution obtained from the differences of the photons arrival times in muon rings: 600 ps
• Digitized data allow post-processing – increasing understanding and performance Oversampling allows noise reduction
• Excellent single photon resolution allows precise inter-calibration
• Excellent timing resolution
fit
1pe
2pe
gain
NEC2013, 8-16 Sept 2013, Varna, Bulgaria 27W. Lustermann, ETH Zurich (for the FACT collaboration)
Single p.e. spectrum all pixels
Dark count spectrum (calirated)• Closed shutter• 1440 pixel• 180k events• All gains normalized to 1• Gain variations: < 6% (temp/time) < 4 % pixel to pixelgain
fit
1pe
2pe
3pe
4pe
5pe
6pe
7pe
8pe
NEC2013, 8-16 Sept 2013, Varna, Bulgaria 28W. Lustermann, ETH Zurich (for the FACT collaboration)
Gain stabilization
1) Compensation for temperature changes• Measure temperatures near the GAPDs• Correct Vbias for the change of Vbd to
maintain Vover constant
2) Compensation for changing NSB conditions• Measure bias currents• Calculate voltage drops and compensate
VbiasVs
Vbias = Vs – R * I(NSB)
3) Verify the stability using the temperature stabilized light pulser installed in the center of the mirror dish
with compensation
without compensation
Achieved gain stability: ~6%
Conclusion: light pulser not required, temperature and bias current based feedback sufficient
NEC2013, 8-16 Sept 2013, Varna, Bulgaria 29W. Lustermann, ETH Zurich (for the FACT collaboration)
Trigger Rate Scans
air showers
Dark night
90% full moon
NSB
Trigger rate scans:• Varying the discriminator thresholds
of the trigger patches• 26 trigger rate scans (Mar – Jul 2012)
Observations with high night sky background (NSB) are possible (full moon) increase of observation time
Trigger rates as function of Vbias
Vbias: (0.8 – 1.6) VNominal: 1.2 V
Digital noise
Gains and trigger system are very stable
air showers
NEC2013, 8-16 Sept 2013, Varna, Bulgaria 30W. Lustermann, ETH Zurich (for the FACT collaboration)
Crab nebula
FACT: CRAB PWN 14.3 h (19.5-29.6.2012) - ‘standard candle’
Significance: 20.8σton / toff = 0.2N excess = 328.8N background = 102.2
Courtesy of NASA/ESA
Hubble: Optical
Chandra: X-ray
NEC2013, 8-16 Sept 2013, Varna, Bulgaria 31W. Lustermann, ETH Zurich (for the FACT collaboration)
Singnals from Markarians
FACT: Mrk 501 – 35.1 h (19.5-29.6.2012)
Significance: 6.6σ ton / toff = 0.2N excess = 101.4N background = 162.6
FACT: Mrk 421 – 23.4 h (28.2-9.5.2012)
Significance: 37.9σ ton / toff = 0.2N excess = 1009.4N background = 269.6
NEC2013, 8-16 Sept 2013, Varna, Bulgaria 32W. Lustermann, ETH Zurich (for the FACT collaboration)
Mrk501 rate
Day (MJD)
rate
/ h
our
excess x 7
Mrk 501 flare (observed by FACT) – send alert to MagicAbout 5 min. of observation would have been sufficient to detect the flare!Monitoring of bright sources with small telescope is possible
alert
stablebackground
NEC2013, 8-16 Sept 2013, Varna, Bulgaria 33W. Lustermann, ETH Zurich (for the FACT collaboration)
Summary/Conclusion
• Electronics system works reliably since 2 years
• Signals from CRAB, Mrk421, Mrk501 observed
• Excellent performance permit bright blazar monitoring
• Minor problems (one DC-DC converter failure, one cooling pump failure solved on site) Join us during observation at:
www.fact-project.org/smartfact