luísa arruda lip – laboratório de instrumentação e física experimental de partículas

Luísa ArrudaLIP – Laboratório de Instrumentação e Física Experimental de Partículas

Jornadas LIP, 7th January 2010 1

The GAW projectA R&D experiment for a very large

field-of-view Imaging Atmospheric Čerenkov Telescope

Observing the High Energy Sky

HeSatellites & Ballons

Satellites

2

Lower Energy Threshold (few tenths of GeV), Improve Flux Sensitivity (in the entire VHE region), Full sky coverage.

The existing and planned ground-based observatories aim to fulfill three main objectives:

IACT Telescopes as CANGAROO III, HESS, MAGIC, VERITAS, … have large collection area reflective optics high spatial resolution;

excellent background rejection;

which allow… wide energy range of -rays: from tens of GeV to TeV; good sensitivity to sources;

but … survey of small sky areas; low detection probability for serendipity transient sources or stables sources far from the galactic plane;

Small field of view (3º-5º) Shower particles arrays ARGO, Tibet-HD and Milagro

very large FoV, more than one steradian large duty cycle sensitivity is some order of magnitude worse than IACT and achieved with much longer exposure.

3Jornadas LIP, 7th January 2010

Current gamma-ray detection techniques

FOV increase in IACTs: limitations


Whipple

Veritas

Large reflector mirrors (up to 17 m Ø) are used by the current IACTs. Field of View enlargement is compromised due to:

image degradation for off-axis imaging

FOV increase in IACTs: limitations


Whipple

Veritas

Large reflector mirrors (up to 17 m Ø) are used by the current IACTs. Field of View enlargement is compromised due to:

image degradation for off-axis imaging

It is necessary to review the current geometry of the IACTs!

the shadow of the focal surface increase

Detector at the focal surface

Mirror(reflective)

Detector at the focal surface

Lens(refractive)

reflective refractive

The GAW concept: Optics GAW proposes the usage of refractive optics to increase the FOV and to avoid the camera shadow

Novel technique using Fresnel lenses: a “refractive” Fresnel lens can work as an efficient light collector!

small thicknessgood transmittanceeasy replication –> low cost solution!

no shadowlarge FoV

RequirementsRequirements:Cromaticity should be controlled at level <0.1º

X (pixels)

016324864

Y (p

ixel

s)

0

16

32

48

64

Instead of the usual charge integration method, GAW front-end electronics design is based on single photoelectron counting mode.

• Keeps negligible the electronics noise and the PMT gain differences.• Strongly reduces the minimum number of p.e. required to trigger the system.

Requirement: pixel size small enough to minimize p.e. pile up within intervals shorter than sampling time (10ns).

The MAPMT R7600-03-M64 chosen as baseline for GAW satisfies such a requirement.

Charge Integration (Analog)

Single Photon Counting (Digital)

• 1 TeV gamma triggered event

• 1 TeV gamma triggered event

pe pile up1 pe2 pe3 pe

The GAW concept: Focal Plane

7

GAW telescope design


Each telescope is equipped with a Fresnel lens a focal surface detector formed by a grid of 10x10 MultiAnode pixelized (8x8) PhotoMultiplier Tubes coupled to light guides.

• GAW is a pathfinder gamma-ray experiment, sensitive in the 1-10 TeV energy region.

• Colaboration between institutes in Italy (IASF, Palermo), Portugal (LIP, Lisbon) and Spain (CIEMAT, Madrid; IAA, Granada).

• The R&D telescope is planned to be located at Calar Alto Observatory (Sierra de Los Filabres - Almeria Spain), at 2168 m a.s.l.

213 cm Ø

50.8 cm Ø40.6 cm

40.6 cm

GAW optics

Jornadas LIP, 7th January 2010

Baseline Optics Module for GAW prototypeLens Flat single-sided

Diameter 2.13 m

Focal Length 2.56 m

f/# 1.2

Material UV Transmitting AcrylicRefraction Index 1.517 (at = 350 nm)

Standard Thickness 3.2 mm

Transmittance ~90% (330-600 nm, from UV to Near Infra Red)

GAW uses a non-commercial Fresnel lens as light collector (by NANOSHAPE). Optimized for maximum of photon detection ( = 360 nm).

central core + 12 petals + 20 petals+ spider support will maintain all the pieces together.

UVT Acrylic B

Transmittance measured for 0.111’’

GAW detection matrix: MAPMT+LG

10

MAPMT 8 × 8 (Hamamatsu R7600-03-M64) UV sensitive [200,680] nm Effective area 18.1 mm x 18.1 mm

Spatial granularity (0.1º) suitable for Cherenkov imaging

Good quantum efficiency for > 300 nm (>20% @ 420 nm) High gain ~3×105 for 0.8 kV voltage, low noise Fast response (< 10 ns) LG are made of 8x8 independent acrylic plastic tubes glued on a plastic plate Tubes pyramidal polyhedron shaped

Lambda (nm)

Qua

ntum

effi

cien

cy


• Luísa Arruda• Pedro Assis• Fernando Barão• Pedro Brogueira• Catarina Espírito Santo• Patrícia Gonçalves• Luís Mendes• Mário Pimenta• Bernardo Tomé

LIP @ GAW: people

LIP @ GAW: responsibilities GAW end-to-end simulation – GAWsoft package EAS simulation Geant4 detector simulation Light guide optimization studies Data analysis tools Electronics firmware Trigger implementation Data handling system & Slow controls


See L. Mendes talk (today, session 3)

LIP @ GAW: responsibilities GAW end-to-end simulation – GAWsoft package EAS simulation Geant4 detector simulation Light guide optimization studies Data analysis tools Electronics firmware Trigger implementation Data handling system & Slow controls ... And have fun with data, doing -ray physics!


See L. Mendes talk (today, session 3)


~55% of the photons would be lost without any guiding device LG are made of 8x8 independent acrylic plastic tubes glued on a plastic plate Tubes:

pyramidal polyhedron shaped material: PMMA from Fresnel Technologies (n=1.4893)

Pieces hold together by 1mm layer on the top made of anti-reflective PMMA A dedicated simulation using Geant4 was done to optimize the LG height

LG vs (X,Y) for <32º

hLG= 20 mm

hLG= 25 mm

26.6 mm

1 mm

hLG

Gap = 0.5 mm

<LG> vs hLG

for FOV [0-12]º

<LG

effi

cien

cy>

(%)

LG height (mm)

<X-Talk> vs hLG

for FOV [0-12]º

hLG = 20-25 mm

LG height (mm)

<X-T

alk>

(%

)

PMMA Fresnel

Light Guides: Optimization studies

Assembled Light Guide

15

Atmosphere

[email protected] 16Jornadas LIP, 7th January, 2010

GAW simulation framework

DET

Very High Energy Gamma Ray Physics Generator (Corsika/user generator);

Air Shower Simulator (Corsika);

• Fresnel Lens

Offline reconstruction

• Light detection + electronics response• Trigger conditions

Telescope Simulator (GEANT4):

Simulate setup: lens + detection matrix response Study the Fresnel lens performance Optimization of the focal plane


GAW simulation framework Motivation

Requirements: Flexibility to simulate different geometries and materials Modularity Different photon sources should be introduced.

[email protected] LIP, 7th January, 2010

GAWsoft package – GAWGAW ssoftware oftware ofoffline fline ttool ool

Datacards

Corsika Data (binary)

Steering Program in C++

Root Tree

Output

Read Datacards

Read Corsika Events

Process events with GEANT4

Event Reconstruction

ASCII

Corsika DATA Corsika DATA

Geant INFO

Fits

18

Receive Input from an External Photon

generator

OR Ext Gen DATA

Run information is stored in a tree (GAWTree_Run) Telescope Coordinates Calar Alto conditions (Temperature,...)

Event information is stored a different tree (GAWTree_Event) MC primary particle MC optical photon @ lens entrance Simulated hits Data hits

Reconstruction parameters

[email protected] 19

Root Output

Jornadas LIP, 7th January, 2010

1 TeV vertical s showers generated in Corsika with NSB

A data analysis package was developed at LIP Based in root

reads the root tree compiled mode

Event display also included: the event display is lauched based on the information stored in branch hits

Commissioning of the GAW telescope in 2010


Aims: Evaluation of the lens optics properties Ø50cm petal Reduced Matrix with 2x2 MAPMTs coupled to LG made of PMMA Optical filters On axis/Off axis observation pointing to Vega Source in Calar Alto

Observatory

Simulation conditions: Vega spectrum for wavelength distribution sampled in the

MAPMT active region [250-600]nm Photons uniformly distributed in the

lens surface Photons pointing downwards N

Vega ~ 46/m2/ns Atmosphere absorption ~75%

MeV

dN/dE (s/m2/s)


Vega spot for on-axis observationFull wavelength spectrum simulated

= (0.11 ± 0.01) º

º03.0

222

pix

lenspix

Where

rec

degree

Snapshot taken in 10ns

GAW timeline

23

2005 - 2007 Telescope Design and site choice


GAW timeline

24


2007 Project proposal approved (Phase 1 approved)


GAW timeline

25


2008 - 2010 Construction and begin of installationLens purchase: lens design First light guide assembled



GAW timeline

26


2008 - 2010


2010-2011 Test full apparatus: 1 telescope 6°×6° FoV

Construction and begin of installationLens purchase: lens design First light guide assembled


GAW timeline

27


2008 - 2010


2010-2011

2011-2012 Results on R&DTest bench for new technological solutions for the focal plane

Construction and begin of installationLens purchase: lens design First light guide assembled


Test full apparatus: 1 telescope 6°×6° FoV

Conclusions

GAW intends to proof that it is possible to combine both good sensitivity with large FOV. GAW will use:

a Fresnel lens as a refractive light collector, single photoelectron counting mode as detection working method.

LIP activity within the collaboration has been crucial for the R&D plan proposed for GAW.

IACT challenges for the next years: Improve sensitivity Lower the threshold for rays detection Higher FOV

Jornadas LIP, 7th January 2010 28

BACKUP Slides



GAW prospects: collecting area

The collecting area is evaluated for mono-energetic -ray events coming from an on-axis source (zenith angle=0°) and with a 3-Fold Telescopes trigger coincidence: the fiducial area (1520×1520 m2) is multiplied by the ratio between the detected and generated events.

GAW and the Crab Nebula.GAW collecting area has been convolved with a Crab-like spectrum.The figure shows the differential detection rate of the Crab Nebula vs energy, which peaks at 0.7 TeV.


GAW prospects: sensitivity

GAW sensitivity with 6°×6° FoV. “Phase 1”

24°×24° FoV

GAW sensitivity with 24°×24° FoV. “Phase 2”

GAW/VERITASGAW light collector (2.13 m Ø) / VERITAS (12 m Ø)GAW is competitive, mainly at higher energies, thanks to the gain of a factor more than 100 in the useful FoV

-> GAW will observe the same sky region for longer exposure time in the same clock-time interval.

The sensitivity limit is evaluated using a source with a Crab-like spectrum.

luísa arruda lip – laboratório de instrumentação e física experimental de partículas

Documents