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

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Electronics Systems Overview

FLV: low voltage conversionFSC slow control (Temp., rel Humidity, voltages)FLP light pulserFDC drive calibration

2 GHz

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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

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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