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Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 Hard X-ray Multilayer Optimisation for Astronomical Missions Hard X-ray Multilayer Optimisation for Astronomical.

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Presentation on theme: "Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 Hard X-ray Multilayer Optimisation for Astronomical Missions Hard X-ray Multilayer Optimisation for Astronomical."— Presentation transcript:

1 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 Hard X-ray Multilayer Optimisation for Astronomical Missions Hard X-ray Multilayer Optimisation for Astronomical Missions

2 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 X-ray Reflection and focalization techniques X-ray Reflection and focalization techniques The problem of multilayer optimisation for hard X ray (E > 10 keV) reflection. The problem of multilayer optimisation for hard X ray (E > 10 keV) reflection. Multilayer mirrors optimisation for future astronomical X-ray projects. Multilayer mirrors optimisation for future astronomical X-ray projects. Conclusions Conclusions

3 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 Minimum detectable flux for past-present-future astronomical missions GOAL!

4 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 Resolving the XRB by focusing optics

5 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 Total reflection the attained geometrical areas are in general very small At photon energies > 10 keV the cut-off angles for total reflection are very small also for heavy metals the attained geometrical areas are in general very small In X ray regions refractive index are close to and little less than 1 for grazing angles lower than a critical angle total reflection phenomenon takes place. Present day focalising telescopes are based on it

6 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 Multilayer mirrors reflection For angles bigger than critical one, reflectivity is low, but not zero.. A multilayer consists in a sequences of bilayers (everyone composed from a couple of light and heavy material), the waves reflected from every interface sum in phase. Constant bilayer thickness (d-spacing) Bragg (constructive interference @ 2d sin q = n ) Variable d-spacing Is possible to obtain high reflectivity on a broader energy band

7 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 1 m Aspidomorpha Tecta; Multilayer for broad band reflection not only in tecnology, but also in nature Natural multilayers (µm, for visible light) Artificial multilayer (nm for X-ray reflection)

8 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 Geometry Wolter I for grazing incidence optics Grazing incidence optics employ nested shells to improve collecting area Every shell is composed of a double profile (parabole + hyperbole in Wolter I design). This scheme gives reduced optical aberrations and a shorter focal length Mirror shell and optical module of SWIFT telescope

9 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 Ni/C multilayer 20 bilayers Dec 2003 E-beam depositionby OAB/Media Lario Ni/C multilayer onto a Si wafer substrate

10 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004

11 How to choose the best thickness values? It is possible to calculate the multilayer reflectivity for a given layers thicknesses sequence but.. It is possible to calculate the multilayer reflectivity for a given layers thicknesses sequence but.. it is generally not possible to analitically design the thicknesses for a given Reflectivity vs Energy response it is generally not possible to analitically design the thicknesses for a given Reflectivity vs Energy response The reflectivity vs energy curve is determined by layers thicknesses sequence The reflectivity vs energy curve is determined by layers thicknesses sequence It can be useful to define a function (function of merit or FOM) whose value indicates how good is the chosen solution It can be useful to define a function (function of merit or FOM) whose value indicates how good is the chosen solution Employing numerical techniques the highest value of the merit function (best design) can be find. Employing numerical techniques the highest value of the merit function (best design) can be find.

12 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 ITERATED SIMPLEX ALGORITHM

13 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 SIMPLEX ALGORITHM (amoeba) It is a quite atypical optimisation technique: It does not require derivative informations The method is LOCAL Applicazione alla funzione di prova: Dato iniziale R C C min E FINE? si no USCITA

14 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 ITERATED SIMPLEX METHOD The SIMPLEX ALGORITHM results are strongly dependent from starting points. ITERATED SIMPLEX METHOD (IS) consists in repeated execution of simplex algorithm, starting every time from different simplexes in parameter space. The software package ISOXM ( Iterated Simplex Optimisation for X-ray Multilayers ) has been developed following this approach. It is possible to obtain results for different functions of merit (FOM). The software comprises tools for results analysis and visualization Crea i dati Legge un dato FINE SIMPLEX FUNZIONE PRINCIPALE no si USCITA Scrive il risultato ISOXM program functional scheme for IS optimisation

15 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 d-spacing sequence described by a power law: PARAMETERS FOR OPTIMISATION the parameter linearly changes along the stack the heavy-material top layer is of increased size + a Carbon overcoating is added to allow a high response in the soft X-ray regime with: a ranging between 0 and b ranging between - and 1 c ranging between 0 and

16 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 Dispersion of parameters after an iterated simplex optimization. Since the starting parameters are generated in a closed region, they are left free to expand.

17 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 Optimization strategy optimized parameters: a, b, c + the slope iterated simplex optimization performed on a small number of selected shells distributed along the sequence of the diameters by using different FOMs Every shell is optimized with a single execution of the simplex algorithm starting from the best result of the previous one sequential optimization of all the shells, based on the results of the immeditely previous optimization. Every shell is optimized with a single execution of the simplex algorithm starting from the best result of the previous one it is possible to combine results obtained from different FOMs for each group of shells, obtaining at the end the more performing total effective area of the telescope.

18 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 Integrated effective area and parameters along shells (XEUS)

19 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 J. Swift – Gulliverss Travels PART I: A VOYAGE TO LILLIPUT XMM XEUS XEUS: a really fantastic telescope……

20 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 XEUS mission

21 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 Mission XMM - XMM -Newton XEUS Number of modules 3 1 10.0 m Max diameter 0.7 m Min diameter 0.3 m 1.3 m Geom. area @ 1 keV 0.15 m2 (per mod.) 30 m 2 Min. angle (I) Min. angle (II) 0.3 deg 0.18 deg 0.7 deg Max. angle (I) Max.angle (II) 0.67 deg 0.7 deg 1.4 deg Angular Resoltion (HEW) 15 arcsec 2 arcsec (goal level) XEUS XMM-Newton Credits: ESA Focal Length 7.5 m 50 m

22 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 LA MISSIONE XEUS

23 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 Mirror Shell, Segments & Petals Mirror Shell, Segments & Petals 562 shell (296 XEUS I + 266 XEUS II) Because of the huge dimensions, Wolter shells must be realized assembling a big number of segments (0.5 m x 1 m x 1 mm). Segments (17500) are grouped in petals (128) that form 5 concentric rings (2 XEUS I + 3 XEUS II). Ø min. XEUS I = 1.3 m Ø max. XEUS I = 4.04 m Ø max. XEUS II = 9.9 m CREDIT: ESA Gli specchi di XEUS

24 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 Extension of the XEUS operative range to hard X-ray (E 80 keV) XEUS I Ogasaka et al., 2003 Even if the XEUS focal length is very large, the f-number are relatively small also for XEUS I (34 -10) only with the use of multilayer supermirrors it is possible the hard X-ray extension of the XEUS operative range study performed in Japan (Nagooya Univ & ISAS) suggested the use of Pt/C supermirrors based on discrete blocks of constant bi-layers with different (constant) d-spacing The supermirror solution is currently being considered by the XEUS Telescope Working Group

25 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 XEUS I optimization: Shells 1-250: N=200, optimization with power law Parameters: a,b,c, Γ 1, Γ N For shells 251-296 N=30 D=80 Å 1/1125-250 - D=80 Å 251-296 1/4119-124 2/41-118 Local minimum F.O.M.Shells XEUS I optimization results: A eff = 2000 cm 2 @ 40 keVA eff = 2000 cm 2 @ 40 keV The number of bi-layers could be further on reduced without a strong impact on the reflectivity Reduction of the deposition time and of the roughness increase

26 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 Multilayer mirrors for XEUS II: a viable and suitable choice? depth-graded multilayer supermirrors for the enhancement of the hard X-ray (E > 10 keV) response are not convenient, since with the XEUS II large angles (0.7 – 1.4 deg) we are far from the Bragg diffraction conditions (2 d sin = n ) at high energy the use of broad-band multilayer supermirrors made of many bi-layers is not viable even below 10 keV, due to the strong photoelectric absorption HOWEVER the soft X-ray (0.5 – 4 keV) response of any high density material (Au, W, Ir, Ni, Pt…) can be increased with the introduction of a low density material overcoating, not sensitive to the photoelectric absorption effects in the total reflection region (and anyway transparent at higher photon energies…) constant d-spacing multilayers (formed by a small number of bilayers) are able to provide narrow high-reflectivity Bragg peaks in the soft X-ray region

27 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 Comparison of the reflectivities of Gold, a W/Si multilayer (with and without a W-thick/C bilayer overcoating) at the incidence angle of 1 deg For XEUS II we assumed a constant d-spacing W/Si multilayer (30 bilayers, d = 80 Å) plus a n overcoating made by: W 80 Å + C 50 Å for all the XEUS II mirror shells

28 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 Effect of the XEUS II Low- Energy Enhancement carbon overcoatingmultilayer Bragg peak

29 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 Test performed at the PANTER-MPE facility (Credits: W. Burkert). Low-energy (0.93 keV) reflectivity enhancement of a Ni mirror by a 50 Å Carbon overcoating: experimental result

30 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 Materi al Youngs Modulus (GPa) Thermal Expansion coefficient (10 6K -1 ) @ 25 o C Breaki ng strengt h (Mpa) Sputteri ng Yield Temperatu re at vapour pressure =10-4/10- 6 ton Possible coupling Ni20013.0 Not available 1.31270/1072C C 6.5 9 (graphite) 7.1 8 15 (graphite) 0.362015/1872 Ni, Pt Pt1688.8 Not available 1.11750/1492C W4114.5 0.602800/2407Si Mo3294.819300.702150/1822Si Si 47 131 2.61200.51340/1147 Mo, W The XEUS optics module will have to operate for a long time in extreme thermal conditions, with the temperature cyclically fluctuating between –30 and –40 °C (depending on the orbit altitude) to prevent fast aging effects, with the increase of the internal stresses and micro-roughness, a good agreement between the CTEs of the two materials of a multilayer could be an obvious advantage. The Pt/C couple appears as a good candidate What are the best material to survive in the very cold XEUS environment?

31 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 Example of Pt/C Multilayer optimisation for future projects Pt Absorption edge at 78.4 KeV

32 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 Thickness variations with depth for different multilayer designs: Bilayers thickness varies from ~20 to >120 Å Accurate control of deposition is needed to achieve high reflectivities.

33 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004

34 The Platinum choice as a reflecting coating Platinum can act, like Gold, as a release agent in the replication process

35 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 the Formation Flight architecture opens the opportunity to realize hard X-ray (E > 10 keV) telescopes based on low grazing angles and large focal lengths Wolter I optics the design of the SIMBOL-X baseline relies on Pt single-layer mirrors with a 30 m focal length, with shell diameters similar to those assumed for XMM (but with much smaller reflection angles) possible improvements of the design can be achieved by increasing the external diameter and using multilayer reflecting coatings for more external shells

36 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 HEXIT-SAT & SIMBOL-X: due missioni per lo studio dellUniverso in raggi X duri tramite ottiche focalizzanti Giovanni Pareschi INAF – Osservatorio Astronomico di Brera (on behalf of large collaborations) Simbol-X HEXIT-SAT

37 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 De Luca e Molendi 2003 Risoluzione del background cosmico X nella regione del picco (~30 keV)

38 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 Uno studio finanziato da ASI (Unità Paylod Elettrottici) è appena iniziato per produrre un prototipo completo (1 mirror shell multilayer sottile + 1 rivelatore CdZnTe) di telescopio per raggi X duri. Scopo dimostrare che in Italia le tecnologie per la realizzazione di un payload a focalizzazione per astronomia in raggi X duri sono ormai mature per una missione satellitare Progetto ASI Progetto preliminare Payload per Astronomia delle alte energie

39 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 Emissione al di sotto di 10 keV : meccanismi termici & non termici La componente non termica è fondamentale per studiare i fenomeni di accrescimento ed accelerazione Gli strumenti realizzati finora presentano una sensibilità peggiore di circa 2 ordini di grandezza in corripondenza della separazione tra fenomeni termici e non termici SIMBOL–X ed HEXIT-SAT sono due missioni al cui studio e proposizione sta partecipando parte della comunità italiana « Alte Energie » per risolvere questo problema introduzione di ottiche focalizzanti per raggi X duri SIMBOL–X & HEXIT-SAT Sensibilità: > 100 volte meglio di INTEGRAL-IBIS (E < 50 keV) Risoluzione angolare: 15 - 30 arcsec HEW Banda energetica di lavoro: 0.5 – 70 keV

40 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 P.I.: P. Ferrando Service dAstrophysique CEA & Fédération de Recherche APC Progetto proposto al CNES (Bando formation flight 2004) da: Francia: Service dAstrophysique CEA Saclay / CESR Toulouse LAOG Grenoble / LUTH Meudon Italia:INAF - Observatorio Astronomico di Brera ( ma interesesse a questa missione già mostrato anche da ricercatori di altri enti in ambito INAF, IASF/CNR e Università) Germania: MPE Garching / PNSensor GmbH München / IAA Tübingen UK: Dept of Astronomy and Astrophysics, Leicester SIMBOL–X Decisione per selezione Studio di Fase A entro Luglio 2004

41 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 P.I.: P. Ferrando Service dAstrophysique CEA & Fédération de Recherche APC Progetto proposto al CNES (Bando formation flight 2004) da: Francia: Service dAstrophysique CEA Saclay / CESR Toulouse LAOG Grenoble / LUTH Meudon Italia:INAF - Observatorio Astronomico di Brera ( ma interesesse a questa missione già mostrato anche da ricercatori di altri enti in ambito INAF, IASF/CNR e Università) Germania: MPE Garching / PNSensor GmbH München / IAA Tübingen UK: Dept of Astronomy and Astrophysics, Leicester SIMBOL–X

42 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 Formation fligth with 30 m focal length Can serve as XEUS pathfinder SIMBOL-X mission concept Main features Operative band: 0.5–70 keV Energetical resolution:< 130 eV @ 6 keV, 1 % @ 60 keV Angular resolution:< 30 arcsec (local. < 3 arcsec) Effective area:>550 cm 2 E < 35 keV 150 cm 2 @ 50 keV Sensibility:5 10 -8 ph/cm 2 /s/keV (E < 40 keV) (5 s, 100 ks, D E = E/2) Si SDD (0.5 – 10 keV) detector+ CdZnTe (10 – 70 keV) detector

43 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 Architettura Formation flight per SIMBOL-X Pointed Telescope Orbita Circolare a 90000 Km di altitudine possibilità di più di 100 ks di osservazioni ininterrotte Posizionamento relativo: ± 1 cm lungo lasse del telescopio ± 1 cm perpendicolare Ricostruzione di assetto: conoscenza della posizione dellasse entro 3 arcsec Orbita a basso bachrground di particelle Almeno due anni di osservazioni reali Missione di classe medium-size

44 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 SIMBOL-X: area efficace in asse

45 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 60 cm diam (baseline) 70 cm diam 80 cm diam + ML

46 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004

47 HEXIT-SAT mission

48 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 HEXIT – SAT (High Energy X-ray Imaging Telescope - SATellite) Mission concept to be realized for main contribute at national level from a researchers of INAF, IASF e Universities. It will be presented to the international community on the occasion of the next SPIE conference in Glasgow (Fiore et al., 2004) It is based on on a multimodular telescope (4 units) with Wolter multilayer mirrors with 8 m of focal length Extensable optical bench to reduce the costs Orbita LEO equatoriale (SAX like) optimal to have a low particles background

49 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 se il d-spacing viene variato in modo continuo (supermirror) e lassorbimento non è eccessivo (raggi X duri, > 10 keV) si possono creare bande di riflessione 3-4 volte maggiori di quelle in riflessione totale per specchi a singolo strato ad es. in Au, Pt, Ir. La distribuzione dei d-spacing segue in questo caso una legge di potenza: d(i) = a / (b+i) c i = indice del bistrato a /(2 sin c ) c 0.25 b> -1 Multilayer a larga banda (supermirrors)

50 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004

51 Number of modules 4 Number of nested mirror shells 50 Reflecting coating 200 bilayers W/Si Geometrical profile Wolter I (lin. approx) Focal Length 8000 mm Total Shell Height 800 mm Plate scale 26 arcsec/mm Total Shell Height 800 mm Material of the mirror walls electroformed Ni Min-MaxTop Diameter 112 - 330 mm Min - Max angle of incidence 0.096 - 0.295 deg Min-Max wall thickness 0.120 - 0.350 mm Total Mirror Weight (1 module) 65 Field-of-View (diameter FWHM 15 arcmin Single module effective area 75 cm 2 @40 keV HEXIT-SAT Main features

52 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 Principali caratteristiche della missione HEXIT-SAT Lifetime 3 + 1 years Lifetime 3 + 1 years Orbital Altitude 600 Km Orbital Altitude 600 Km Mass 1000 Kg (TBC) Mass 1000 Kg (TBC) Orbit Duration 95 min Orbit Duration 95 min Scientific Data Center: ASI SDC (Frascati) Scientific Data Center: ASI SDC (Frascati) Ground Stations: Ground Stations: #1 Malindi Lat: - 3.14 o, Long: 40.05, Alt.: 0 Km Visibility @ 3.5 o orbit: 150min/day – 650 sec/orbit Visibility @ 50 o orbit: 35 min/day – 500 sec/orbit (with large spread min/max) (with large spread min/max) #2 Fucino Lat: 42.0 o, Long: 13.50, Alt.: 0 Km Visibility @ 3.5 o orbit: No Tracking Visibility @ 50 o orbit: 65 min/day – 550 sec/orbit (with large spread min/max) (with large spread min/max)

53 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 4 modules

54 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 Effects of using different FOMs The design can be chosen according to the mission target The design can be chosen according to the mission target

55 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 Summary and conclusions The software ISOXM ( Iterated Simplex Optimisation for X-ray Multilayers ) for global Optimisation with different FOMs has been developed. The numerical optimization of depth-graded supermirrors described by power- laws for several missions has been executed with good results. future work will be done to study a possible reduction of the number of bi-layers compared to the 200 units assumed for this study. The study showed a consistent increase of the XEUS effective area in the energy region between 0.5 and 5 keV. At larger incidence angles multilayer reflectors can be employed to enhance the reflectivity at low energies by mean of constant d-spacing multilayers with Carbon overcoating. The study showed a consistent increase of the XEUS effective area in the energy region between 0.5 and 5 keV. the carbon overcoating could be useful, not only to enhance the reflectivity in the soft X-ray region, but also to prevent aging effects due to the exposure to Atomic Oxigen fluxes.

56 Vincenzo Cotroneo – OAB Merate/INAF 8/11/2004 The End


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