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HIFI Beam Properties, Results and Impact HIFI Performance

HIFI Beam Properties, Results and Impact HIFI Performance. Status Report HIFI Science Verification Review #2 SRON Groningen, Tuesday 5 December 2006 Willem Jellema, Marinus Jochemsen and Tully Peacocke. FM3 Results: Beam Parameters in FP.

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HIFI Beam Properties, Results and Impact HIFI Performance

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  1. HIFI Beam Properties, Results andImpact HIFI Performance Status Report HIFI Science Verification Review #2 SRON Groningen, Tuesday 5 December 2006 Willem Jellema, Marinus Jochemsen and Tully Peacocke

  2. FM3 Results: Beam Parameters in FP • Projection on M3 obtained for situation after FM2. From left to right band 1 to 7. Telescope axis pointing out of paper. • Presentation provides update beam parameters for flight.

  3. FM3 Results: Waist Size in FP • All bands have compliant focal-plane beam sizes • Deviation expected in band 7 due to out-of-band measurement @ 1620 GHz instead of 1800 GHz

  4. FM3 Results: Y Coordinate in FP • There is no requirement on the absolute position in the FP as long as M2 alignment and co-alignment requirements are met • Co-alignment defined as fitted offset two Gaussians.

  5. FM3 Results: Z Coordinate in FP • Systematic offset in chopper direction. Edge detection test of M3 revealed this is a systematic measurement error. • Co-alignment error in band 5 due to monocle without reshim.

  6. FM3 Results: X Coordinate in FP • Measured focus nicely follows focal plane curvature of Herschel telescope. • Again, there are long-wave optics effect showing up as apparent defocus.

  7. FM3 Results: Tilt about Y in FP • Tilt perpendicular to M3, pupil co-alignment on M2. • Nearly all bands compliant with requirements.

  8. FM3 Results: Tilt about Z in FP • Tilt along M3, pupil co-alignment on M2. • Larger deviations found. In some cases due to Gaussian fitting method, in some cases probably due to scattering

  9. FM3 Results: Optical Performance Parameters • Total loss for all bands below 6% budgetted for (ignoring apparent loss due to long-wave effects) • Co-alignment best in band 6 and 7. Co-alignment does generally not satisfy 10% of waist size criteria.

  10. FM3 Results: Tilt about Z in FP • Tilt along M3, pupil co-alignment on M2. • Larger deviations found. In some cases due to Gaussian fitting method, in some cases probably due to scattering

  11. Summary and Conclusions • Overall the (quasi-)optical alignment is very good. • Optical coupling losses will stay below 6%. • Co-alignment is generally 20-30% of waist size or 10-15% of FWHM at sky • Losses per polarization channel when re-pointing to average position at sky typically 1-3% • There is a large systematic measurement error (2-3 mm) in the absolute position of the beams in the focal-plane • Error analysis is ongoing. Source of error not yet identified. • Only important for prediction nominal pointing at sky. Will not affect conclusions about compliance or co-alignment.

  12. Status Error Analysis (1) • Absolute positions of beams show deviations of order 2-3 mm • Errors in M3 bracket and TPD alignment can be ignored • Lateral offset of 0.4 mm found in relative position horn aperture and cross on scanner AD. Diagonal horn in band 6/7 not properly mounted. Offset to be calibrated. • Most FM1 and FM2 measurement have been done using the wrong scanner AD, i.e. the penta-prism reflection. Correction scheme in development. • Scanner plane bends under load of radiation shields. Errors of order 2-3’ or 0.3-0.4 mm in FP. • Bug in drift calibration routine identified. Effect can be as large as 0.5 mm in FP, but is much smaller (~0.1 mm) in most bands. • Most likely error is a significantly wrong orientation of AD on scanner combined with smaller errors listed above. Re-calibration ongoing.

  13. Status Error Analysis (2) • Edge detection test on M3 in band 2 revealed systematic error in measurement system • Repeated FM3 beam measurements before and after weekend: identical results within measurement error • Repeated FM3 measurement at 3 mm/s, 5 mm/s, 8 mm/s and 11 mm/s: identical results within measurement error • Repeated FM3 measurements at same measurement grid parameters and settings as used during FM1: identical results • Repeated FM3 measurements with and without airco: identical results • Other than systematic alignment error in scanner system (recalibration and analysis ongoing) measurements reproduce well and relative error between beam parameters –H and –V can be accurately measured

  14. Status Error Analysis (3) • Phase flex error map measured at room temperature on measurement grid. Phase error due to cables less than 10º at 1.6 THz. • Polarization effect recently detected. As beams are not always measured along their main polarization axis, a cross-polar error beam is added. Effect can be quite large, typically 0.5 up to 1.5 mm. Analysis and simulations going on. • HIFI BS1 grids are not all perfect. Loss in transmission seems to result in cross-polar reflection. This implies that the polarization of MSA-V rotates at the grid. • Polarization interfaces of HIFI not verified. Assume polarization ray-tracing is right. Test source polarization might be aligned even worse relative to polarization axes of FP beams. • Need for additional experimental verification. Measurement of orthogonality of –V and –H channels. Can probably be combined with one of the testmodes involving re-imager.

  15. Status Error Analysis (4) • Separate parallel test-setup will be prepared to characterize polarization rotation effect in diplexer configuration. • Representative simulations are being carried out. • Finally, alignment method using theodolite will be (re-)verified. Has been succesfully appplied at MSA level for shimming. • Here, different configuration, with mylar window as transmission element in between alignment devices and large distance involved. • Room-temperature testbed will be setup mimicing ILT configuration. • Data-reduction procedure related to coordinate system transformations (connecting scanner to spacecraft coordinates) will be done from scratch by independent person.

  16. Status Error Analysis (5) Absolute positions FP spots deviate of order 2-3 mm

  17. Status Error Analysis (6) Scanner plane bends under weight shields

  18. Status Error Analysis (7) Residual phase error due to bug in drift calibration

  19. Status Error Analysis (8) Residual phase error due to bug in drift calibration

  20. Status Error Analysis (9) Polarization different for each band; measure at average

  21. Status Error Analysis (10) Cross-polar beam originates from M11-M10-M9. Level is Typically -19 to -23 dB.

  22. Status Error Analysis (11) Polarization rotation strongly increases with transmission loss

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