This page is http://space.mit.edu/HETG/swg497.html
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Each of the gratings on the flight HETG has been X-ray tested in the MIT X-ray Grating Evaluation Facility, X-GEF. These sub-assembly data are used to generate the predicted Effective Efficiency and, along with HRMA predictions, the predicted HRMA-MEG and HRMA-HEG Effective Areas.
The Resolving Power of the HETGS is the result of several major terms, detailed in a Resolving Power Error Budget.
At the subassembly level the period and period variations of each facet are measured by a Laser Reflection setup. These period variations, "dp/p", are the main HETG contribution to the LSF in the dispersion direction. Regarding the cross-dispersion blur, the polarization-alignment of the facets to the HETG support structure is the main fabrication contributor.
The measurements broadly divide into LSF related and Effective Area related. Depending on the calibration phase, focal plane detector, different types of measurements were carried out.
These examples give a feel for the range of data taken at XRCF.
|Focus Check||-||verify focus||verify focus||verify focus||-|
|Alignment||-||gross vignetting, mis-aligned gratings||-||-||-|
|PSF/Inner||-||-||core, wings; offaxis images||-||core, wings; offaxis images|
|PSF/1D||LSF core, wings||-||-||-||-|
|3D: Offaxis||-||offaxis images||-||-||-|
|EE||Order locations, Effective area||-||-||-||-|
|3D: EA||Effective area, high orders||Source spectra||-||-||-|
|EA||Effective area||-||Effective area||Effective area||Effective area|
|3D: Molec. Contam.||-||edges, etc.||-||-||-|
|Molec. Contam.||-||-||edges, etc.||-||edges, etc.|
|dF: Molec. Contam.||-||-||edges, etc.||-||-|
Some key "scalar" calibration values deduced/confirmed from XRCF measurements are tabulated below. The measured periods are based on a Rowland distance of 8782.8 mm, Al-K line E = 1.4867 keV, and an assumed accuracy of the HXDS prime Y stage encoders.
|MEG period||4000.77||~ 0.10||A||LR/NIST gives: 4001.13 +/- 2.00|
|HEG period||2000.95||~ 0.10||A||LR/NIST gives: 2000.81 +/- 0.05|
|MEG Angle||4.74||0.05||deg.s||CEI spec 5.0 +/- 0.5|
|HEG Angle||-5.19||0.05||deg.s||CEI spec 5.0 +/- 0.5|
|MEG-HEG Angle||9.93||0.01||deg.s||CEI spec 10.0 +/- 0.7|
|LEG period||9903.90||~ 0.30||A||expect 9912.5|
|LEG Angle||0.006||0.05||deg.s||CEI spec 0.0 +/- 0.5|
The gratings at XRCF are able to give detailed spectra of the XRCF sources. This information is particularly needed for Grating Effective Area measurements to know what fraction of BND or focal plane detected counts are in the desired line.
Data analysis is still in process for effective area / efficiency measurements.
There is much data to analyze, however some conclusions are possible at this time.