Stix Aspect System

Pascal Saint-Hilaire, Martin Fivian, and Gordon Hurford

STIX meeting/teleconSSL, 2006/12/20

STIX:

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

Google search for “Fresnel Zone Plate”:

1-D FZP:combination of FZP + slit:

Front tray Rear tray

CCD array

Get two limbs in one direction

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

Radiation pattern in plane parallel to aperture

At 1 AU…

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

At 1 AU:

Typical Power on walls:Centered & Worst case:0.7% (12cm)0.2% (14cm)

At .22 AU:

Power on walls:Centered:0.69% (12cm)0.24% (14cm)

Worse case:1.03% (12cm)0.44% (14cm)

At 5.2 AU:

Typical power on walls:Centered & worst case:0.67% (12cm)0.22% (14cm)

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

“preset diameter algorithm”

In reality, should have 10-50 times more pts to fit!

“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.

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