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 2 W. Lustermann, ETH Zurich (for the FACT collaboration) Cherenkov spectrum 2.2 km altitude Cut off ~320 nm Signal amplitude: 200 photons / m 2 (1 TeV γ-ray) Spectrum: (300 – 600) nm Duration: few ns Night sky: up to several GHz Signal amplitude: 200 photons / m 2 (1 TeV γ-ray) Spectrum: (300 – 600) nm Duration: few ns Night sky: up to several GHz Optical imaging system (causes losses) Mirror  light concentrators  photo-detectors 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 3 W. Lustermann, ETH Zurich (for the FACT collaboration) GOAL: 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) ns The 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 4 W. Lustermann, ETH Zurich (for the FACT collaboration) Refurbished HEGRA CT3 Mirror area: 9.5 m 2 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 5 W. Lustermann, ETH Zurich (for the FACT collaboration) 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 6 W. Lustermann, ETH Zurich (for the FACT collaboration)

NEC2013, 8-16 Sept 2013, Varna, Bulgaria 7 W. Lustermann, ETH Zurich (for the FACT collaboration) FLV:low voltage conversion FSCslow control (Temp., rel Humidity, voltages) FLPlight pulser FDCdrive calibration 2 GHz

NEC2013, 8-16 Sept 2013, Varna, Bulgaria 8 W. Lustermann, ETH Zurich (for the FACT collaboration) Photo detectors: Hamamatsu MPPC active area: 3 x 3 mm pixels of (50  m) 2 Operation voltage: ~70 VGain (nominal): 7.5 x 10 5 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 area Limiting angular (watch only the mirror)

NEC2013, 8-16 Sept 2013, Varna, Bulgaria 9 W. Lustermann, ETH Zurich (for the FACT collaboration) FLV:low voltage conversion FSCslow control (Temp., rel Humidity, voltages) FLPlight pulser FDCdrive calibration 2 GHz

NEC2013, 8-16 Sept 2013, Varna, Bulgaria 10 W. Lustermann, ETH Zurich (for the FACT collaboration) 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 11 W. Lustermann, ETH Zurich (for the FACT collaboration) FLV:low voltage conversion FSCslow control (Temp., rel Humidity, voltages) FLPlight pulser FDCdrive calibration 2 GHz

NEC2013, 8-16 Sept 2013, Varna, Bulgaria 12 W. Lustermann, ETH Zurich (for the FACT collaboration) 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 13 W. Lustermann, ETH Zurich (for the FACT collaboration) 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 14 W. Lustermann, ETH Zurich (for the FACT collaboration) FLV:low voltage conversion FSCslow control (Temp., rel Humidity, voltages) FLPlight pulser FDCdrive calibration 2 GHz

NEC2013, 8-16 Sept 2013, Varna, Bulgaria 15 W. Lustermann, ETH Zurich (for the FACT collaboration) 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 16 W. Lustermann, ETH Zurich (for the FACT collaboration) FLV:low voltage conversion FSCslow control (Temp., rel Humidity, voltages) FLPlight pulser FDCdrive calibration 2 GHz

NEC2013, 8-16 Sept 2013, Varna, Bulgaria 17 W. Lustermann, ETH Zurich (for the FACT collaboration) 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 18 W. Lustermann, ETH Zurich (for the FACT collaboration) FLV:low voltage conversion FSCslow control (Temp., rel Humidity, voltages) FLPlight pulser FDCdrive calibration 2 GHz

NEC2013, 8-16 Sept 2013, Varna, Bulgaria 19 W. Lustermann, ETH Zurich (for the FACT collaboration) 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 20 W. Lustermann, ETH Zurich (for the FACT collaboration) 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 21 W. Lustermann, ETH Zurich (for the FACT collaboration) 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 22 W. Lustermann, ETH Zurich (for the FACT collaboration) 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 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 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 23 W. Lustermann, ETH Zurich (for the FACT collaboration) 1) 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 24 W. Lustermann, ETH Zurich (for the FACT collaboration)

NEC2013, 8-16 Sept 2013, Varna, Bulgaria 25 W. Lustermann, ETH Zurich (for the FACT collaboration) DIM: Distributed Information Management System (CERN) Qt4

NEC2013, 8-16 Sept 2013, Varna, Bulgaria 26 W. Lustermann, ETH Zurich (for the FACT collaboration) 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 27 W. Lustermann, ETH Zurich (for the FACT collaboration) Dark count spectrum (calirated) Closed shutter 1440 pixel 180k events All gains normalized to 1 Gain variations: < 6% (temp/time) < 4 % pixel to pixel gain fit 1pe 2pe 3pe 4pe 5pe 6pe 7pe 8pe

NEC2013, 8-16 Sept 2013, Varna, Bulgaria 28 W. Lustermann, ETH Zurich (for the FACT collaboration) 1) Compensation for temperature changes Measure temperatures near the GAPDs Correct V bias for the change of V bd to maintain V over constant 2) Compensation for changing NSB conditions Measure bias currents Calculate voltage drops and compensate V bias VsVs V bias = V s – 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 29 W. Lustermann, ETH Zurich (for the FACT collaboration) 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 V bias V bias : (0.8 – 1.6) V Nominal: 1.2 V Digital noise Gains and trigger system are very stable air showers

NEC2013, 8-16 Sept 2013, Varna, Bulgaria 30 W. Lustermann, ETH Zurich (for the FACT collaboration) FACT: CRAB PWN 14.3 h ( ) - ‘standard candle’ Significance: 20.8σ t on / t off = 0.2 N excess = N background = Courtesy of NASA/ESA Hubble: Optical Chandra: X-ray

NEC2013, 8-16 Sept 2013, Varna, Bulgaria 31 W. Lustermann, ETH Zurich (for the FACT collaboration) FACT: Mrk 501 – 35.1 h ( ) Significance: 6.6σ t on / t off = 0.2 N excess = N background = FACT: Mrk 421 – 23.4 h ( ) Significance: 37.9σ t on / t off = 0.2 N excess = N background = 269.6

NEC2013, 8-16 Sept 2013, Varna, Bulgaria 32 W. Lustermann, ETH Zurich (for the FACT collaboration) Day (MJD) rate / hour excess x 7 Mrk 501 flare (observed by FACT) – send alert to Magic About 5 min. of observation would have been sufficient to detect the flare!  Monitoring of bright sources with small telescope is possible alert stable background

NEC2013, 8-16 Sept 2013, Varna, Bulgaria 33 W. Lustermann, ETH Zurich (for the FACT collaboration) 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) 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: Join us during observation at: