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Grazing-incidence vs. normal-incidence design

EUS Meeting March, 3rd 2006. Grazing-incidence vs. normal-incidence design. L. Poletto CNR - National Institute for the Physics of Matter Department of Information Engineering - Padova (Italy). slit. spectrometer. telescope. detector. Normal-incidence vs. grazing-incidence design (1/2).

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Grazing-incidence vs. normal-incidence design

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  1. EUS MeetingMarch, 3rd 2006 Grazing-incidence vs. normal-incidence design L. Poletto CNR - National Institute for the Physics of Matter Department of Information Engineering - Padova (Italy)

  2. slit spectrometer telescope detector Normal-incidence vs. grazing-incidence design (1/2) EUS BLOCK DIAGRAM TELESCOPE: two options 1) normal-incidence, single mirror 2) grazing-incidence, three mirrors SLIT SPECTROMETER normal-incidence VLS concave grating DETECTOR APS

  3. Normal-incidence vs. grazing-incidence design (2/2) THE MAIN DIFFERENCE BETWEEN THE TWO CONFIGURATIONS IS THE TELESCOPE DESIGN THE SPATIAL AND SPECTRAL RESOLUTIONS OF THE NI CONFIGURATION ARE HIGHER THAN THE GI ONE THE TWO DESIGNS MAY OFFER THE SAME SPECTRAL COVERAGE (NI NEEDS MULTILAYER FOR WAVELENGTHS BELOW 35 NM)

  4. The grazing-incidence Wolter telescope Grazing-incidence telescope two concave mirrors and a plane mirror rastering: rotation of the plane mirror CHARACTERISTICS 114-126 nm spectral region (I order) 57-63 nm spectral region (II order) 18 arcmin  18 arcmin field-of-view length <1 m

  5. Grazing-incidence design: characteristics Telescope Wolter II Focal length1200 mm Incidence angles 73.5 deg - 79 deg Mirror for rastering Incidence angles 84.4 deg - 85 deg Slit Size 6 mm  6.3 mm Resolution 1 arcsec Grating TVLS Groove density 2400 lines/mm Entrance arm 260 mm Exit arm 680 mm Spectral region 114-126 nm (I order) 57-63 nm (II order) Detector Pixel size 10 mm  15mm Format 2150  1120 pixel Area 21.5 mm  16.8 mm Spectral resolving element 56 mÅ I order (14 km/s) 28 mÅ II order (14 km/s) Spatial resolving element 1 arcsec (150 km at 0.2 AU) Instrument length 1 m

  6. Grazing-incidence design: performance

  7. Grazing-incidence design: layout

  8. NI coatings (1/2) Mo-Si multilayer Au SiC

  9. NI coatings (2/2) Mo-Si mulilayer good reflectivity (0.3) at 20, 60, 100 nm low reflectivity (0.38) in the visible  HIGH ABSORBED POWER Au no reflectivity at 20 nm low reflectivity (0.15) at 60, 100 nm high reflectivity (0.80) in the visible  LOW ABSORBED POWER SiC no reflectivity at 20 nm high reflectivity (0.40) at 60, 100 nm low reflectivity (0.20) in the visible  HIGH ABSORBED POWER THE NI TELESCOPE IS EFFICIENT BELOW 40 NM ONLY WITH MULTILAYER

  10. GI coatings (1/2) Au or Si-Au Au at 80 deg

  11. GI coatings (2/2) Au constant reflectivity at 20, 60, 100 nm high reflectivity (> 0.80) in the visible  LOW ABSORBED POWER Si-Au constant reflectivity at 20, 60, 100 nm (higher than Au) high reflectivity (> 0.60) in the visible  LOW ABSORBED POWER THE GI TELESCOPE IS EFFICIENT AT ANY WAVELENGTH ABOVE 10 NM

  12. Efficiency Total efficiency at wavelength l ETOT(l) = A [cm2]  E(l) PS [arcsec2] AEF entrance aperture E(l) combined efficiency (telescope, spectrometer, detector) at wavelength l PS pixel size CDS on SOHO, NIS2 channelETOT_CDS(60 nm) = 0.046

  13. Efficiency at 20 nm GI design AEF = 25 cm2 Egrating = 0.15 Edetector = 0.30 Si-Au coated optics Rmirrors = 0.55, 0.65, 0.75 ETOT(20 nm) = 0.30 = EFFICIENCY @60nm Au coated optics Rmirrors = 0.40, 0.52, 0.70 ETOT(20 nm) = 0.16 = EFFICIENCY @60nm NI design AEF = 25 cm2 Egrating = 0.15 Edetector = 0.30 ML coated optics Rmirrors = 0.30 ETOT(20 nm) = 0.34 = EFFICIENCY @60nm

  14. Efficiency at 60 nm Grazing-incidence design at 60 nm AEF = 25 cm2 Egrating = 0.15 Edetector = 0.30 Si-Au coated optics Rmirrors = 0.55, 0.65, 0.75 ETOT(60 nm) = 0.30 = 6.6 CDS EFFICIENCY Au coated optics Rmirrors = 0.40, 0.52, 0.70 ETOT(60 nm) = 0.16 = 3.5 CDS EFFICIENCY Normal-incidence design at 60 nm AEF = 25 cm2 Egrating = 0.15 Edetector = 0.30 SiC (ML) coated optics Rmirrors = 0.32 ETOT(60 nm) = 0.36 = 7.8 CDS EFFICIENCY Au coated optics Rmirrors = 0.13 ETOT(60 nm) = 0.15 = 3.2 CDS EFFICIENCY

  15. Efficiency at 120 nm Grazing-incidence design at 120 nm AEF = 25 cm2 Egrating = 0.15 Edetector = 0.30 Si-Au coated optics Rmirrors = 0.55, 0.65, 0.75 ETOT(120 nm) = 0.30 = EFFICIENCY @60nm Au coated optics Rmirrors = 0.40, 0.52, 0.70 ETOT(120 nm) = 0.16 = EFFICIENCY @60nm Normal-incidence design at 120 nm AEF = 25 cm2 Egrating = 0.15 Edetector = 0.30 SiC coated optics Rmirrors = 0.48 ETOT(120 nm) = 0.54 = 1.5 EFFICIENCY @60nm Au coated optics Rmirrors = 0.16 ETOT(120 nm) = 0.18 = 1.2 EFFICIENCY @60nm

  16. Optics degradation at 20 nm Multilayer coating A change of the ML properties (e.g. interdiffusion between adjacent layers, change of period due to thermal expansion) may alter the reflectivity down to 0. THE ML IS A “SINGLE POINT FAILURE” FOR OBSERVATIONS AT 20 NM. THE STABILITY OF ML AT THE EXTREME THERMAL CONDITIONS OF SOLO HAS TO BE PROVED BY STUDIES AND TESTS, IN VIEW OF THE AO.

  17. Optics degradation at 100 nm Simulation of a C over-coating GI reflectivity (80 deg) Au 0.55 Au + 20 Å C 0.53 -3% Au + 40 Å C 0.52 -5% NI reflectivity SiC 0.45 SiC + 20 Å C 0.31 -30% SiC + 40 Å C 0.23 -50% LARGE DECREASES FOR NI COATINGS

  18. Optics degradation in the visible Simulation of a C over-coating GI reflectivity at 600 nm (80 deg) Au 0.92 Au + 20 Å C 0.90 -2% Au + 40 Å C 0.88 -4% NI reflectivity at 600 nm SiC 0.20 SiC + 20 Å C 0.21 +5% SiC + 40 Å C 0.22 +10% SMALL CHANGES

  19. Thermal load: GI (1/2) Grazing-incidence configuration: 5 cm × 5 cm entrance area Input thermal load 85 W Au optics Thermal load on 1st mirror 85 W 6 solar constants Absorption on 1st mirror 17 W 1.2 solar constants Thermal load on 2nd mirror 61 W 16 solar constants Absorption on 2nd mirror 10 W 2.6 solar constants Thermal load on 3rd mirror 19 W 5 solar constants Absorption on 3rd mirror 2 W 0.5 solar constants Power density on the slit plane 17 W on 21 mm  30 mm area (f = 1200 mm) 20 solar constants Comments 29 W absorbed by the optics (two of them have to be cooled) 39 W absorbed by suitable buffling 17 W on the slit plane, to be absorbed by buffles

  20. Thermal load: GI (2/2) Grazing-incidence configuration: 5 cm × 5 cm entrance area Input thermal load 85 W Si-Au optics Thermal load on 1st mirror 85 W 6 solar constants Absorption on 1st mirror 34 W 2.4 solar constants Thermal load on 2nd mirror 46 W 12 solar constants Absorption on 2nd mirror 18 W 5 solar constants Thermal load on 3rd mirror 10 W 2.7 solar constants Absorption on 3rd mirror 4 W 1 solar constant Power density on the slit plane 6 W on 21 mm  30 mm area (f = 1200 mm) 7 solar constants Comments 56 W absorbed by the optics (all are cooled) 23 W absorbed by suitable buffling 6 W on the slit plane, to be absorbed by buffles

  21. Thermal load: NI (1/2) Normal-incidence configuration: 5 cm × 5 cm entrance area, 1 m input boom, 5 cm × 5.6 cm mirror Input thermal load 85 W Thermal load on the buffle 22 W Thermal load on the mirror 63 W 16 solar constants SiC optics Absorption on the mirror 50 W 13 solar constants Power density on the slit plane 13 W on 33 mm diameter (f = 700 mm) 11 solar constants Comments 50 W absorbed by the mirror 22 W absorbed by the entrance buffle 13 W on the slit plane, to be absorbed by buffles Au optics Absorption on the mirror 13 W 3.4 solar constants Power density on the slit plane 50 W on 33 mm diameter (f = 700 mm) 43 solar constants Comments 13 W absorbed by the mirror 22 W absorbed by the entrance buffle 50 W on the slit plane, to be absorbed by buffles

  22. Thermal load: NI (2/2) ML coated optics Absorption on the mirror 40 W 13 solar constants Power density on the slit plane 23 W on 33 mm diameter (f = 700 mm) 20 solar constants Comments 40 W absorbed by the mirror 22 W absorbed by the entrance buffle 23 W on the slit plane, to be absorbed by buffles

  23. Some considerations on the entrance filter • As proposed in the Astrium Payload Integration Study, an entrance filter could reduce to zero the thermal load on the optics. • A suitable filter for the 60 nm region is a thin Al foil (200 nm, 0.6 transmission) • VERY RISKY SOLUTION: single point failure • FEASIBLE ? • Grazing-incidence configuration • The filter is on the entrance aperture • Thermal load on the filter • 25 solar constants on the Al foil • Normal-incidence configuration • The filter is inserted at the end of the entrance tube (0.8 m) • 20 solar constants on the Al foil

  24. Conclusions NI DESIGN The NI configuration is more compact and has better optical performance than the GI one. A multilayer coated mirror is required for observations below 40 nm. GI DESIGN No multilayer coated mirrors are required AT PRESENT, NI CONFIGURATION IS THE FIRST CHOICE (GI AS A BACKUP SOLUTION). GIVEN THE EXTREME THERMAL CONDITIONS ON SOLO (34 kW/m2), TESTS AND STUDIES ON COATING DEGRADATION AT NORMAL-INCIDENCE (BOTH CONVENTIONAL AND MULTILAYERS) HAVE TO BE PERFORMED IN VIEW OF THE AO.

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