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

Normal-incidence vs. grazing-incidence design (1/2) EUS BLOCK DIAGRAM telescope slit spectrometer detector TELESCOPE:two options1) normal-incidence, single mirror 2) grazing-incidence, three mirrors SLIT SPECTROMETERnormal-incidence VLS concave grating DETECTORAPS

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)

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

Grazing-incidence design: characteristics TelescopeWolter II Focal length1200 mm Incidence angles73.5 deg - 79 deg Mirror for rastering Incidence angles84.4 deg - 85 deg Slit Size6 m 6.3 mm Resolution1 arcsec GratingTVLS Groove density2400 lines/mm Entrance arm260 mm Exit arm680 mm Spectral region nm (I order) nm (II order) Detector Pixel size10 m 15 m Format pixel Area21.5 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

Grazing-incidence design: performance

Grazing-incidence design: layout

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

NI coatings (2/2) Mo-Si mulilayergood reflectivity (0.3) at 20, 60, 100 nm low reflectivity (0.38) in the visible HIGH ABSORBED POWER Auno reflectivity at 20 nm low reflectivity (0.15) at 60, 100 nm high reflectivity (0.80) in the visible LOW ABSORBED POWER SiCno 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

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

GI coatings (2/2) Auconstant reflectivity at 20, 60, 100 nm high reflectivity (> 0.80) in the visible LOW ABSORBED POWER Si-Auconstant 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

Efficiency Total efficiency at wavelength E TOT ( ) = A [cm 2 ] E( ) PS [arcsec 2 ] A EF entrance aperture E( )combined efficiency (telescope, spectrometer, detector) at wavelength PSpixel size CDS on SOHO, NIS2 channelE TOT_CDS (60 nm) = 0.046

Efficiency at 20 nm GI design A EF = 25 cm 2 E grating = 0.15 E detector = 0.30 Si-Au coated opticsR mirrors = 0.55, 0.65, 0.75 E TOT (20 nm) = 0.30 = Au coated opticsR mirrors = 0.40, 0.52, 0.70 E TOT (20 nm) = 0.16 = NI design A EF = 25 cm 2 E grating = 0.15 E detector = 0.30 ML coated opticsR mirrors = 0.30 E TOT (20 nm) = 0.34 =

Efficiency at 60 nm Grazing-incidence design at 60 nmA EF = 25 cm 2 E grating = 0.15 E detector = 0.30 Si-Au coated opticsR mirrors = 0.55, 0.65, 0.75 E TOT (60 nm) = 0.30 = 6.6 CDS EFFICIENCY Au coated opticsR mirrors = 0.40, 0.52, 0.70 E TOT (60 nm) = 0.16 = 3.5 CDS EFFICIENCY Normal-incidence design at 60 nmA EF = 25 cm 2 E grating = 0.15 E detector = 0.30 SiC (ML) coated opticsR mirrors = 0.32 E TOT (60 nm) = 0.36 = 7.8 CDS EFFICIENCY Au coated opticsR mirrors = 0.13 E TOT (60 nm) = 0.15 = 3.2 CDS EFFICIENCY

Efficiency at 120 nm Grazing-incidence design at 120 nmA EF = 25 cm 2 E grating = 0.15 E detector = 0.30 Si-Au coated opticsR mirrors = 0.55, 0.65, 0.75 E TOT (120 nm) = 0.30 = Au coated opticsR mirrors = 0.40, 0.52, 0.70 E TOT (120 nm) = 0.16 = Normal-incidence design at 120 nmA EF = 25 cm 2 E grating = 0.15 E detector = 0.30 SiC coated opticsR mirrors = 0.48 E TOT (120 nm) = 0.54 = 1.5 Au coated opticsR mirrors = 0.16 E TOT (120 nm) = 0.18 = 1.2

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.

Optics degradation at 100 nm Simulation of a C over-coating GI reflectivity (80 deg) Au0.55 Au + 20 Å C % Au + 40 Å C % NI reflectivity SiC0.45 SiC + 20 Å C % SiC + 40 Å C % LARGE DECREASES FOR NI COATINGS

Optics degradation in the visible Simulation of a C over-coating GI reflectivity at 600 nm (80 deg) Au0.92 Au + 20 Å C % Au + 40 Å C % NI reflectivity at 600 nm SiC0.20 SiC + 20 Å C0.21+5% SiC + 40 Å C % SMALL CHANGES

Thermal load: GI (1/2) Grazing-incidence configuration: 5 cm × 5 cm entrance area Input thermal load85 W Au optics Thermal load on 1st mirror85 W 6 solar constants Absorption on 1st mirror17 W 1.2 solar constants Thermal load on 2nd mirror61 W16 solar constants Absorption on 2nd mirror10 W2.6 solar constants Thermal load on 3rd mirror19 W5 solar constants Absorption on 3rd mirror2 W0.5 solar constants Power density on the slit plane17 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

Thermal load: GI (2/2) Grazing-incidence configuration: 5 cm × 5 cm entrance area Input thermal load85 W Si-Au optics Thermal load on 1st mirror85 W 6 solar constants Absorption on 1st mirror34 W 2.4 solar constants Thermal load on 2nd mirror46 W12 solar constants Absorption on 2nd mirror18 W5 solar constants Thermal load on 3rd mirror10 W2.7 solar constants Absorption on 3rd mirror4 W1 solar constant Power density on the slit plane6 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

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 load85 W Thermal load on the buffle22 W Thermal load on the mirror63 W16 solar constants SiC optics Absorption on the mirror50 W 13 solar constants Power density on the slit plane13 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 mirror13 W3.4 solar constants Power density on the slit plane50 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

Thermal load: NI (2/2) ML coated optics Absorption on the mirror40 W 13 solar constants Power density on the slit plane23 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

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

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.