EUS NI spectrograph design constraints

1. EUS NI spectrograph design constraints • Contents: • design of normal-incidence spectrograph with ZEMAX • optical quality of the single-mirror off-axis telescope • possibility of three wavelength ranges between 58 nm and 126.8 nm • design of focal plane with 116.8 nm to 126.8 nm channel • some thoughts on thermal aspects: • Semi-transparent telescope mirror • Heat rejection mirror Udo Schühle Max-Planck-Institute for Solar System Research Solar Orbiter 5th EUS consortium Meeting at RAL on 3. March 2006

2. normal-incidence design optical calculations • Based on previous design of Roger Thomas: • development of varied-line-space grating surface for ZEMAX • ZEMAX calculation with ellipsoid VLS grating • modified RT design for longer wavelength channel • verified the design complies with specs • some possible thermal design solutions

3. off axis parabola telescope: aperture size: 70 mm distance from vertex: 45 mm focal length: 600 mm image scale: 1arcsec = 3.0 microns spectrograph: magnification: 3.9 image scale: 12 mm/arcsec dispersion: 5 A/mm spectral scale: 60 mA/12mm (40 mA/8mm) Wavelengths: 54 -64 nm 70 – 80 nm 97 -106.2 nm R. Thomas design of NI spectrograph

4. off axis parabola telescope: aperture size: 70 mm distance from vertex: 50 mm focal length: 700 mm image scale: 1arcsec = 3.4 microns spectrograph: magnification: 3.6 image scale: 12 mm/arcsec dispersion: 5 A/mm spectral scale: 60 mA/12mm (40 mA/8mm) Wavelengths: 70 – 80 nm 97 -104 nm 116.7 -126.8 nm (57 – 63 nm) Design of NI spectrograph 1 arcsec

5. Design of single-mirror telescope off axis parabola telescope: aperture size: 70 mm distance from vertex: 50 mm focal length: 700 mm image scale: 1arcsec = 3.4 microns 1 arcsec 1 arcsec

6. Accommodation of three wavelength bands possible? • favoured wavelength ranges : 52 nm – 63 nm • 72 nm – 80 nm • 97 nm – 104 nm • 116.5 nm – 126.8 nm • possible with siliconcarbide optics • normal incidence design with three wavelength ranges from 58.0nm to 126.8nm

7. Accommodation of three wavelength bands possible! 900 mm 70 mm slit • 71.0 nm • 80.0 nm 250 mm • 97.0 nm • 104.5 nm TVLS grating • 116.5 nm (58 nm) • 126.8 nm (63 nm) 700 mm

8. Accommodation of long-wavelength band Si III C III N V C I Si I Mg X O V Mg X He I O IV

9. Accommodation of long-wavelength band More useful dynamic range with selective photocathode distribution Presentation of wavelength channels to be given by Luca Teriaca

10. Study of a dichroic telescope mirror for 58 nm up • mirror coating for wavelengths 58 nm and up: SiC (CVD, hex) • a thin coating of ~10 nm provides good VUV reflectivity of 35% to 45% • longer wavelengths can be transmitted by a transparent substrate • mirror temperature can be minimised • detailed thermal study is possible. •  dichroic telescope mirror can transmit 90% of the heat!

11. Study of a dichroic telescope mirror for 58 nm up Calculations of David Windt 2001 using optical constants of SiC

12. Study of a dichroic telescope mirror for 58 nm up 10 nm SiC on LiF substrate* independent study is ongoing with samples of SiO2 and SiC coating of 5 nm, 10 nm, 20 nm thickness * calculation using optical constants of Palik et al. ==> heat will be transmitted towards a radiator

13. Design of single-mirror telescope:heat rejection mirror and baffle • field of incident radiation at slit plane: +-2.6° (= size of solar image + pointing range) • corresponds to circular range of 64 mm diameter! • unpredictable thermal distortions during orbit and pointing changes • unpredictable stray light in front of the spectrometer slit  toroidal pre-slit mirror

14. Design of single-mirror telescope:heat rejection mirror and baffle radiator radiator toroidal heat rejection mirror

15. Thermal baffle design requires space for heat rejection mirror 900 mm 70 mm slit • 75.0 nm • 85.0 nm 250 mm • 97.0 nm • 104.0 nm TVLS grating • 116.5 nm (58 nm) • 126.8 nm (63 nm) heat rejection mirror 700 mm