Analysis Plan for the first Al Grating Measurements --------------------------------------------------- Dan Dewey, 12/17/96, 1/3/97 file: XRCF /home/dd/text/Al_analysis_plan.txt , MIT ~dd/xrcf/Al_analysis_plan.txt This is an overview (with some details) of the grating measurements planned for the first Al phase measurements. These notes are organized by measurement order. Note that % is used to indicate I,L, or H in a TRW ID when different gratings appear in a single suite. Shutter Focusses, D-%XH-SF-1.001 - 1.003 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ These three shutter focusses will set the FOA for the grating measurements. The first one, with the LETG, will be exciting with one (possibly both) of the first orders visible on the HSI as well as the LETG cross-diepersion spectrum (see simulation.) The MEG and HEG will show continuum at ~ 5 degree angle. The four images that result from the SCAN can be combined into a complete image. The intensity of the four images can be compared to each other and to the equivalent images from the no-grating HSI ALL,SCAN Shutter Focuss(es) (D-IXH-SF-3.001) Ratios of the total counts in zero-order from these grating data to the total counts in the no-grating data, corrected for source flux, can be used for a measure of: vignetting*grating_Effic(1.487,0). [Where grating_Effic(E,m) is the grating membrane efficiency at E into order m. dd to produce write-up summarizing the sub-assembly efficiency data available...] The LETG Shutter Focus X value should be very close to the HRMA-only full shell value. Depending on reality the LETG FOA (Facility Optical Axis) may be adjusted to have a better FWHM in the dispersion direction (with a slight increase in the cross-dispersion blur.) Note that the HRMA "all" FOA was used in Phase 1C for C-LXH-3D-2.001, the Al LETG mosaic. Focus Checks, C-%XH-SF-1.004 - 1.009 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ The quadrant HSI images can be used to verify that the HSI is moving on the Rowland Circle as desired by showing that +1 and -1 order images are both in focus (+/- 3 for LETG). Or perhaps there will be an HXDA yaw (rotation about z) that will cause one order to be defocussed in one direction and the other in the opposite direction. By comparing the zero-order images (from Shutter Focus) with the first-order (third-order) images taken here, upper limits (hopefully!!) can be put on the grating dp/p period variation values by looking at any increase in the diffracted beam FWHM (y direction) from the no-grating beam. PSF Tests, C-HXH-FC-1.010 - 1.011 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ These two tests (on MEG +3 order and HEG +2 order) will add of course, more information about the HSI-on-Rowland-circle question (above) and more importantly, they will allow better dp/p limits to be set. By comparing the dispersion blur of the first orders with these higher orders, the effects of source line width and grating dp/p can be determined independent of any zero-order (off-energy) effects. Alignment/Vignetting Tests, C-%XH-AL-4.001 - 4.005 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ These tests use well-out-of-focus HSI images to measure and set limits on the vignetting of the HRMA rays when a grating is inserted in the beam. Before (no-grating) and after images are taken. The shell-by-shell azimuthal ratio between these images gives shell overall vignetting and azimuthal variation of vignetting. A significant azimuthal variation in vignetting could be the result of a grating-HRMA decenter mis-alignment. It is expected that LETG shell 1 will show approximately 3.6% more vignetting than LETG shells 3,4, and 6 due to the non-ideal axial location of the gratings. Tilt of the nominally on-axis HRMA may also introduce the equivalent of a decenter between the HRMA rays and the grating apertures. LETG Al Mosaic, C-LXH-3D-2.001 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ This set of 11 HSI images will be useful for a variety of purposes, most of which are outlined in the Grating Mosaics section further below. DISPERSION ANGLE Of immediate interest (and why it is moved ahead of the HETG Alignment tests) is the use of the LETG mosaic to determine a value for the LETG dispersion direction with respect to the prime-Y direction. This angle can be fedback through the expander s/w parameters (in cleanup.awk) to provide better angles for crucial grating EE measurements (C-%XF-EE-3.001-3.015). The dispersion angle in HSI coordinates can be determined by the line between diffraction orders in a single exposure and/or by the angle of the continuum. The prime-Y direction in HSI coordinates can be determined by the line connecting a given order in one image to the same order in another image. The LETG mosaic is the only one where the same order appears in multiple images. HSI pore angle Test, C-HXH-AL-4.003 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Because the HRMA rays hit the HSI at various angles depending on the shell and azimuth from which they come, the ring focus images (without grating) will likely show azimuthal intensity variations due to the HSI pore-angle effect. This image is a defocussed HEG second order image of shells 4 and 6 - the grating dispersion will cause these rays to hit the HSI at an additional angle of 0.47 degrees. Analyzing this image with the others may be able to determine the HSI pore-angle bias direction. HSI-Grating Mosaic Images, C-%XH-3D-2.001-2.003 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Several interesting things result from these tests. RELATIVE DISPERSION ANGLES By using the continuum to define a line in each HSI image the angles of the gratings in the HSI coordinates can be determined. Thus the relative angle between gratings can be determined and used to update the grating parameters. ORDER INTENSITY The relative intensity of the orders in the HSI mosaic can be used to see if the grating high-order predictions are ball-park accurate. SPECTRAL FEATURES The continuum spectrum from the mosaics can be extracted and qualitatively compared to the expected spectrum, e.g., edges present. Coarse Dispersion Measurements, C-%XF-EE-3.001-3.006 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ The prime prupose of these beam center measurements on grating 0 and +1 orders is to get precise period/angle values for the gratings as mounted at XRCF. To minimize the chance of missing the order (failed beam center) the measurements are made in increasing distance from 0 order. The results (angle, period, rowland distance) from these measurements will be input to the expander to update the CMDB for the Fine Dispersion Measurement set that follows. Intervening HRMA measurements should allow time for calculation. These measurements are the first grating ones using the FPC in the focal plane and can yield values for 0 and +1 order that should be accurate. BND data can be used to normalize the effective area. Fine Dispersion Measurements, C-%XF-EE-3.007-3.015 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ The prime purpose of these beam center measurements on order -1 and higher orders (+/- 9 for LETG, +/- 3 for MEG, and +/- 2 for HEG) is to get more precise period/angle values for the gratings as mounted at XRCF. The results (angle, period, rowland distance) from these measurements will be input to the expander to update the CMDB for many measurements that follow, in particular the Al FPC/SSD order measurements (-3D-26.xxx). Intervening HRMA measurements should allow time for calculation and CMDB update before suite 26 is executed. Because these use the FPC, efficiencies/effective area for orders -1, +/- high-order can be calculated for a range of pinholes too. These can also be used to normalize the HSI mosaic to obtain efficiencies in orders up to 5. BND data can be used to accurately include corrections for source flux variations. Grating Effective Area at Al ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ The measurement set C-%XF-3D-26.001 to C-%XS-3D-26.016 consists of eight measurements with the FPC and the same repeated with the SSD. The discussion below references the FPC measurements - similar comments apply to the SSD equivalents (add 8 to the value, e.g., 26.001 FPC --> 26.009 SSD equivalent.) Except for the largest orders LETG set, a pinhole size of 500 um is used. 26.001 and 26.002 are the no-grating MEG,HEG references with shells 1,3 and 4,6 open respectively. Combined these give the LETG reference. 26.003 is MEG -4 to +4 order. Note that the actual order of measurements is +1,+2,+3,+4,0,-1,-2,-3,-4 (determined by the IDL .loc creating s/w cmdb_make_locs.pro). This ordering has the brightest order selected first to avoid operator panic when the weaker orders appear. 26.004 is the test of the HEG +1,+2,0,-1,-2 orders. The next four measurements are for the huge number of LETG orders and are arranged in the sets: 26.005 +1,+3,0,-1,-3 26.006 +2,+3,+4,+5,+6,+7,-2,-3,-4,-5,-6,-7 26.007 +7,+8,+9,+10,+11,+12,+13,+14,-7,-8,-9,-10,-11,-12,-13,-14 Switching to 2000 um pinhole: 26.008 +15,+16,+17,+18,+19,+20,+21,+22,+23,+24,+25,-15,-16,-17, -18,-19,-20,-21,-22,-23,-24,-25 This extensive data set, includeing the BND data, can be used to determine the LETG, MEG, and HEG efficiencies and effective areas in the various orders. The HSI images and EE data previously obtained can be used with these data to assess what fraction of the total m-th order flux is intercepted by the measurement pinhole and apply corrections as needed. One of the crucial test planning activities based on the analysis of these Suite 26 data is to determine the relative value (sensitivity, background rate in line, fittablility, etc.) of SSD vs FPC focal plane measurements. All other grating effective area tests are currently specified to use the FPC. For energies above Al the SSD should be considered. Finally, the agreement or not of the SSD and FPC effective areas (and efficiencies which may have less systematics involved) will give us an indication of the accuracy we are obtaining. - - - - - - end of Grating Al measurements - - - -