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The GAW project. A R&D experiment for a very large field-of-view Imaging Atmospheric Čerenkov Telescope. Luísa Arruda LIP – Laboratório de Instrumentação e Física Experimental de Partículas. Observing the High Energy Sky. Satellites & Ballons. He. Satellites. - PowerPoint PPT Presentation
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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
4Jornadas LIP, 7th January 2010
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
5Jornadas LIP, 7th January 2010
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
8Jornadas LIP, 7th January 2010
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
11Jornadas LIP, 7th January 2010
• 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
12Jornadas LIP, 7th January 2010
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!
13Jornadas LIP, 7th January 2010
See L. Mendes talk (today, session 3)
14Jornadas LIP, 7th January 2010
~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
17Jornadas LIP, 7th January 2010
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
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
21Jornadas LIP, 7th January 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)
22Jornadas LIP, 7th January 2010
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
Jornadas LIP, 7th January 2010
GAW timeline
24
2005 - 2007 Telescope Design and site choice
2007 Project proposal approved (Phase 1 approved)
Jornadas LIP, 7th January 2010
GAW timeline
25
2005 - 2007 Telescope Design and site choice
2008 - 2010 Construction and begin of installationLens purchase: lens design First light guide assembled
2007 Project proposal approved (Phase 1 approved)
Jornadas LIP, 7th January 2010
GAW timeline
26
2005 - 2007 Telescope Design and site choice
2008 - 2010
2007 Project proposal approved (Phase 1 approved)
2010-2011 Test full apparatus: 1 telescope 6°×6° FoV
Construction and begin of installationLens purchase: lens design First light guide assembled
Jornadas LIP, 7th January 2010
GAW timeline
27
2005 - 2007 Telescope Design and site choice
2008 - 2010
2007 Project proposal approved (Phase 1 approved)
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
Jornadas LIP, 7th January 2010
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
29Jornadas LIP, 7th January 2010
30Jornadas LIP, 7th January 2010
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.
31Jornadas LIP, 7th January 2010
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.