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Stix Aspect System
Pascal Saint-Hilaire, Martin Fivian, and Gordon Hurford
STIX meeting/teleconSSL, 2006/12/20
The Fresnel Zone Plate (FZP) as a lens:
Aperture spacing such that wavelets emitted from each successive aperture are ~one wavelength apart (i.e. 2-phase difference) when they arrive at P, where they interfere constructively.
P
FZP for STIX:
• two orthogonal 1-D FZPs (x & y directions)• Slit width constraints: size of diffraction patch,
has to be large enough to reach detector even when Sun is off-axis, and limited enough so that we do not have reflexion off walls of STIX. We settled for 25 m.
• Taking 25 m to be the smallest FZP dimension, one gets an FZP with 228 apertures, for a total diameter of 22.8 mm.
Center portion of the proposed FZP to be etched (i.e two 1-D FZPs):
Width: 25 m
Overall size: 22.8 x 22.8 mm
At 1 AU…Contours:Red: 1, 3, 10, 30%Yellow: 50, 70, 90%Blue: Sun
Power on walls:0.7% (12cm)0.2% (14cm)
“X” FZP (projected from top tray)
“Y” FZP (projected from top tray)
CCD arrays
Limb detection schemes:
• 1) Heritage from RHESSI SAS:
• 2) Method from Gordon: “preset diameter algorithm”: uses the fact that we know what the diameter of the Sun is
“Conclusions”
• Power on walls: typically 0.7% for 12cm, 0.2% for 14cm; worst case: 1% or 0.4%.
• Limb detection algorithm: will test it thoroughly
• Predicted accuracy: better than 1”
• Will built and test prototype in the next few months.