march 2, 2007 r. mirzoyan: cta paris meeting; mount & mirror wg report mount and mirror (mm)...

March 2, 2007 R. Mirzoyan: CTA Paris Meeting; Mount & Mirror WG Report

Mount and Mirror Mount and Mirror (MM) Working (MM) Working Group ReportGroup Report

Presented by Razmick MirzoyanPresented by Razmick MirzoyanOn behalf of the MM working On behalf of the MM working

groupgroup

Max-Planck-Institute for Physics, MunichMax-Planck-Institute for Physics, Munich


HESS II – 600m²

Sizes of few well-known telescopes

HEGRA – 8.3m²

HESS I – 108m²

MAGIC – 239m²

Ø 5m = small Ø 20m = largeØ 10m = medium Ø 30m = hugeDISH

FoV 4° - 5°normal

6° - 12°wide new


Size of a telescopeSize of a telescope

Currently we have quite some Currently we have quite some experience with constructing experience with constructing telescopes of sizes ranging from telescopes of sizes ranging from

(3 – 17) m in (3 – 17) m in .. Within next 2 years we will start Within next 2 years we will start

collecting experience also with a collecting experience also with a 28m H.E.S.S. telescope. 28m H.E.S.S. telescope.


Choice of the size of a Choice of the size of a telescopetelescope

The choice of the size of a telescope is The choice of the size of a telescope is dictated by the desired dictated by the desired

a) energy thresholda) energy threshold

b) field of view (FoV) b) field of view (FoV)

c) optical resolution in the given FoV c) optical resolution in the given FoV

d) location altituded) location altitude

e) also, type of the used light sensors e) also, type of the used light sensors (future trend)(future trend)

f) last but not least : available financial f) last but not least : available financial supportsupport


The estimated energy The estimated energy thresholdsthresholds

TelescopeTelescope # telescopes x# telescopes x

mirror mirror ,m,mTrigger Trigger

threshold, threshold, GeVGeV

Analysis Analysis threshold, threshold,

GeVGeV

HEGRAHEGRA 5 x 4m5 x 4m 500500 (500) 1000(500) 1000

HEGRA CT-1HEGRA CT-1 1 x 4.3m1 x 4.3m 500500 (750) 1000(750) 1000

CATCAT 1 x 5m1 x 5m 300300

H.E.S.S.-IH.E.S.S.-I 4 x 12m4 x 12m 100100 160160

VERITASVERITAS 4 x 12m4 x 12m ~like ~like H.E.S.S.-IH.E.S.S.-I

~like ~like H.E.S.S.-IH.E.S.S.-I

CANGAROO-CANGAROO-IIIIII

3 (4) x 10m3 (4) x 10m 250250 500500

MAGIC-IMAGIC-I 1 x 17m1 x 17m 5050 100100

H.E.S.S.-IIH.E.S.S.-II 1 x 28m1 x 28m 2525 5050

MAGIC-IIMAGIC-II 2 x 17m2 x 17m 3030 5050

The EThe Ethresholdthreshold shall scale with the shall scale with the of a telescope as of a telescope as E ~ 1/{E ~ 1/{}²}²


IACTs comparative table IACTs comparative table TelescopeTelescope HEGRAHEGRA H.E.S.S.H.E.S.S. MAGICMAGIC VERITASVERITAS CANGACANGA

ROOROO

#, #,

(m)(m)5 +1 5 +1

4.34.34 (+1)4 (+1)

12 (28)12 (28)1 (+1)1 (+1)

17 (17)17 (17)44

121244

1010

Mirror Mirror Area, m²Area, m²

(5 x 8.3) (5 x 8.3) ++

(1 x 10) (1 x 10)

(4 x 108) (4 x 108) ++

(1 x 600)(1 x 600)

(1 x 239) (1 x 239) ++

(1 x 239)(1 x 239)

4 x 1104 x 110 4 x 574 x 57

ReflectorReflector

DesignDesignDavies-Davies-CottonCotton

Davies-Davies-Cotton + Cotton + (Parabolic(Parabolic) )

Parabolic Parabolic ++

ParabolicParabolic

Davies-Davies-CottonCotton

ParabolicParabolic

f/#f/# 1.21.2 1.21.2

1.21.211 11 0.80.8

Weight, TWeight, T (5 x 2.4) (5 x 2.4) ++

1 x 41 x 4

(4 x 60) +(4 x 60) +

1 x 5001 x 50064 +64 +

6464

Geom. Geom. FoVFoV

5 x 4.5° +5 x 4.5° +

1 x 3.7°1 x 3.7°4 x 4.5°4 x 4.5°

1 x 3°1 x 3°3.9° +3.9° +

3.9°3.9°4 x 3.5°4 x 3.5° 4 x 3.2°4 x 3.2°


Comparison exampleComparison example

TelescopTelescopee

HEGRAHEGRA

K€K€H.E.S.S.-H.E.S.S.-II

K€K€

H.E.S.S.-H.E.S.S.-IIII

K€K€

MAGIC-I MAGIC-I K€K€

MAGIC-MAGIC-IIII

K€K€

FoundatiFoundationon

4 x 60.-4 x 60.- 450.-450.- 250.-250.- 260.-260.-

Rail Rail systemsystem

nono 4 x 15.-4 x 15.- 120.-120.- 39.-39.- 44.-44.-

Material Material ++

EngineeriEngineeringng

5 x 70.-5 x 70.-K€K€

4 x 300.-4 x 300.-

4 x 50.-4 x 50.-3200.-3200.-

1000.-1000.-720.-720.- 820.-820.-

Total Total InvestInvest

Cost, K€Cost, K€

<1000<1000 12000.-12000.- 12000.-12000.- 4000.-4000.- 4600.-4600.-

In optical astronomy the cost of a telescope scales ~ {}2.6

It seems that the cost of an IACT can be scaled ~ {}2.2


Mechanical constraintsMechanical constraints

Space frame, dimensions, weight,… materials:• Steel: very big experience, thermal expansion O’K, stiff,

heavy• Aluminium: innovative, expensive, twice higher thermal

expansion than steel, light. No corrosion.• Carbon Fibre reinforced plastics: innovative, thermal

expansion is just 7 % from that of Al, very stiff, very light. Avoid excessive heat. ~ 2 times more expensive than steel.

Thermal Thermal

expansiexpansionon

ConcreConcretete

Glass,Glass,

ordinaordinaryry

SteeSteell

AlAl Carbon fibre Carbon fibre

reinforced reinforced plasticplastic

(x10(x10-5-5 °C°C-1-1))

1.21.2 0.90.9 1.31.3 2.2.44

0.20.2


Exapmle CFRP frame: Exapmle CFRP frame: MAGIC-IMAGIC-I

Deformation of the mirror dishCamera support, bending vs. elevation

Possible hysteresis of deformations


CTA Design criteriaCTA Design criteria Stereoscopic telescope system (>> 4 telescopes)Stereoscopic telescope system (>> 4 telescopes) Alt-Az mount on railsAlt-Az mount on rails Davies-Cotton for small dishes, parabola for large dishes Davies-Cotton for small dishes, parabola for large dishes

(> 10m)(> 10m) Segmented mirror facetts, possibly ~ 1m size for large Segmented mirror facetts, possibly ~ 1m size for large

dishesdishes F/D > 1F/D > 1 Robust, simple, reliable system (lifetime > 10 years), Robust, simple, reliable system (lifetime > 10 years),

robotic operation desired, keeping robotic operation desired, keeping maintenance/operation effort lowmaintenance/operation effort low

Survival winds > 160 km/hSurvival winds > 160 km/h Consider protection during ice, snow, below 0 Consider protection during ice, snow, below 0

temperaturestemperatures


Design criteriaDesign criteria Weight of the camera (will depend on the level of Weight of the camera (will depend on the level of

integration of electronics inside the camera)integration of electronics inside the camera) Positioning and pointing accuracyPositioning and pointing accuracy Stiffness of the structure and/or AMC systemStiffness of the structure and/or AMC system Safety conceptSafety concept

Human safetyHuman safety Protection of the instrumentProtection of the instrument Redundancy in power, drivesRedundancy in power, drives


MechanicsMechanics Tracking precision: like optical telescopesTracking precision: like optical telescopes Positioning accuracy, speedPositioning accuracy, speed Fast slewing: (MAGIC:180°/50sec; H.E.S.S.: Fast slewing: (MAGIC:180°/50sec; H.E.S.S.:

~twice slower; VERITAS: 1°/1sec)~twice slower; VERITAS: 1°/1sec) Drive typeDrive type

GearGear Tooth rimsTooth rims FrictionFriction


Arrival Time FrontArrival Time Front No arrival time No arrival time

distortion for the distortion for the parabolic designparabolic design

Special 2 component Special 2 component optical telescope optical telescope designs may provide no designs may provide no (or almost no) arrival (or almost no) arrival time distortionstime distortions

The wide-spread Davies-The wide-spread Davies-Cotton design provides Cotton design provides ~ 3-4 ns time smearing ~ 3-4 ns time smearing for existing telescopesfor existing telescopes

The RMS of the pulses from The RMS of the pulses from , , hadrons and µ after PMT and hadrons and µ after PMT and

jitter simulationsjitter simulationsMirzoyan, Sobczynska, et al., 2006


Light sensor typeLight sensor type

Classical PMTs: currently used in all Classical PMTs: currently used in all IACTs: Best Photon Detection IACTs: Best Photon Detection Efficiency Efficiency

(PDE): ~ 30 % (PDE): ~ 30 % HPDs with Ga AsP can offer HPDs with Ga AsP can offer

interesting alternatives. PDE ~ 45 % interesting alternatives. PDE ~ 45 % (QE: 50-55 %) (rather expensive)(QE: 50-55 %) (rather expensive)

SiPM: mature product in 3-5 years SiPM: mature product in 3-5 years time. Can offer PDE ~ 60 %time. Can offer PDE ~ 60 %


Observations of the Crab Nebula with H.E.S.S.; astro-ph/0607333v1

Field of ViewField of View

• Currently H.E.S.S. has the largest FoV of all existing IACTs.• Still, as one can see from the left figure, the effective field of view is „only“ ~3° in (@ 3db=0.7 level)• One may think either to provide a) a „large enough“ FoV, so that it can include inside the largest possible gamma source ( 5° ?) or b) really large FoV of (10-20)° for the all sky survay.


Prime focus optics: what is Prime focus optics: what is feasible ?feasible ?

3´ optical resolution

Schliesser & Mirzoyan, Astrop. Phys., 2005


Wide FoVWide FoV Also, the (10-20)° FoV can offer the advantage of Also, the (10-20)° FoV can offer the advantage of

very high optical angular resolution of ~ 1 arc very high optical angular resolution of ~ 1 arc minute everywhere in the FoV. minute everywhere in the FoV.

Simulation results indicate further improvement of Simulation results indicate further improvement of the angular resolution, especially at low energies, the angular resolution, especially at low energies, when moving from currently used when moving from currently used (3-6)´ towards 1´. (3-6)´ towards 1´.

A proper design can offer almost no distortion of A proper design can offer almost no distortion of the arrival time front.the arrival time front.

Schmidt designSchmidt design: can offer interesting solutions : can offer interesting solutions for Wide FoV for Wide FoV

Interesting recent design, Interesting recent design, Ritchey-ChretienRitchey-Chretien: : Vassiliev, et al., astro/ph 0612718Vassiliev, et al., astro/ph 0612718


Wide FoVWide FoV


Which mount is better ?Which mount is better ?

The above question is very much justified:The above question is very much justified:

1.1. A heavy and stable mount, with marginal A heavy and stable mount, with marginal deformations: approach chosen by deformations: approach chosen by HEGRA, H.E.S.S., VERITASHEGRA, H.E.S.S., VERITAS

2.2. A light-weight mount that allows for small A light-weight mount that allows for small deformations, which are actively correctd deformations, which are actively correctd for: approach chosen by MAGIC.for: approach chosen by MAGIC.

In the 2nd case the telescope consists of In the 2nd case the telescope consists of (mount + active mirror correction (AMC) (mount + active mirror correction (AMC) system).system).


Example Active Mirror Example Active Mirror Control (AMC) SystemControl (AMC) System

Star adjust option of AMC:On figure left one can see~12 % of all mirrors in the Camera centre, the rest are Defocused.All the mirror can be Checked in 8 such figures.This will take ~ 10 minutestime + some off-line work.In addition, the reflectivity of all individual mirrors canregularly be measured.


Which mount is the Which mount is the best ?best ?

We have collected positive experience We have collected positive experience with Alt-Az H.E.S.S. and MAGIC type with Alt-Az H.E.S.S. and MAGIC type mounts on rails.mounts on rails.

A combination of a stiff mount + an AMC A combination of a stiff mount + an AMC system could offer an interesting system could offer an interesting solution.solution.This can be interesting for This can be interesting for largelarge and and hugehuge telescopes, especially for large telescopes, especially for large zenith angle observations. zenith angle observations.

We have enough expertise to cope with We have enough expertise to cope with this problem.this problem.


H.E.S.S.-2 mirrorsH.E.S.S.-2 mirrors

H.E.S.S.-Imirror


H.E.S.S.-2 mirror H.E.S.S.-2 mirror candidatescandidates


H.E.S.S.-2 mirrorsH.E.S.S.-2 mirrors


All-All-AlAl MAGIC-I mirrors MAGIC-I mirrors

The MAGIC-I mirrors have size 0.5 m x 0.5 m. 4 of them are set together, forming a panel 1 m x 1 m. MAGIC-I uses 956 mirrors of size 0.5 m x 0.5 m. They are grouped in 239 panels of 1 m x 1 m.

The single 0.5 m x 0.5 m mirrors are obtained by gluing two aluminum sheets on a “honeycomb” structure. After rough pre-milling, a diamond “fly-cutting” of the surface will generate a spherical

surface of a desired radius, having a microroughness of about 100 Å


Upgrade of manufacturing Upgrade of manufacturing process process

of MAGIC mirrors made in of MAGIC mirrors made in PaduaPadua

Monolithic 1 m x 1 m mirrors do not need a support panel and the pre-alignment.

A sandwich formed by two aluminum skins with inserted an “honeycomb” structure is assembled.

The aluminum skins are pre-curved and glued on the honeycomb using a concave spherical mould. Afterwards a diamond milling of the surface is performed to refine the spherical surface. Very positive test results!


New INAF-OAB technology in collaboration with Padua and with Medialario Techn. – foresee the cold shaping of a sandwich made with 2 thin glass sheets (1.7mm) glued on an Al honeycomb (20mm) structure.

While the radius of curvature of the mirror is large and the thickness of the glass sheet is rather thin, it can be conformed to the shape of a

convex master by means of vacuum suction.

Advantages of the glass-faced panels:

Low cost. Lightweight. Doesn’t need polishing either of the glass/master. These characteristics permit to have:

Competitive costs compared to other technologies Superior performance High production speed

Cold Slumping ApproachCold Slumping Approach


Mould and panel produced in Mould and panel produced in Medialario Tech.Medialario Tech.

Aluminum master 1040 x 1040 mm

Front and rear of a produced segment

Size = 985 x 985 mm Weight = 10 Kg.

Nominal radius= 35 m

1m x 1m mirror tests at ETH


Point Spread FunctionPoint Spread Function

90% of the light inside 0.9 mrad 80% of the light inside 0.6 mrad

Achieved parameters already within the MAGIC-II specifications


Developments with Developments with potentialpotential

• Dielectric mirror coatings can offer an interesting alternative:one can „boost“ the mirror reflectivity in the entire wavelengthrange 300-700 nm to ~ 100 %. Needs development work.• Aspheric mirrors are another interesting development direction.They can offer the advantage of better PSF.


Conclusions MMConclusions MM

Telescope Mount:Telescope Mount: quite some experience quite some experience with several types, that can be used in CTA.with several types, that can be used in CTA.

MirrorsMirrors: experience with several types, the : experience with several types, the cost varies between ~(1.2 – 2.5).-k€/m² for cost varies between ~(1.2 – 2.5).-k€/m² for large quantities. We will need to use a large quantities. We will need to use a robust technology, the reflectivity shall not robust technology, the reflectivity shall not seriously deteriorate within 5-10 years.seriously deteriorate within 5-10 years.

Wide FoVWide FoV telescope designs may offer telescope designs may offer interesting solutions, we need to explore interesting solutions, we need to explore their potential.their potential.

march 2, 2007 r. mirzoyan: cta paris meeting; mount & mirror wg report mount and mirror (mm)...

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