HETG Gratings
HETG Gratings
(updated 01/25/98)
Go to HETG at XRCF
Introduction
The data file HETGgratings.rdb
contains one line for each of the flight HETG grating facets (in the
same order as HESSbuilt.rdb). The
file's columns provide an assortment of general and useful information
about the HETG facets. These columns are described in the sections
below.
General Columns
These columns consist of general information about the grating,
its fabrication, and testing.
- entry
- This integer is a unique number assigned to each grating or sample
received by the NE80 test lab.
- frame
- This string is the set of characters inscribed on the grating frame
to uniquely identify the grating. The initial letter (M/H) indicates
an HEG or MEG grating. The remaining 4 or 5 characters have no
specific meaning.
- ne80
- This string gives the [M]M/[D]D/YY date when the grating was received
in NE80.
- wafer
- This string identifies the fabrication wafer ("device") of
the grating. The first 3 characters are the fabrication
lot, e.g., F12 is "flight lot 12". The next H or M indicates
HEG or MEG gratings. Finally, the last three characters are the
wafer number within the lot.
- type
- This single-character string indicates the grating-line
orientation w.r.t. the frame ("gluing angle".) An "A" type
grating can only be mounted in HESS sectors A or AA, etc.
- errsml
- This number is the measured error in degrees between the as-glued
grating line angle and the designed value. Taken at face value, these
"errors" would be compensated for during the grating-to-HESS alignment
process and result in the grating frame being rolled from the design
value.
- acoustic
- This value is the resonant frequency in Hz of the grating membrane.
- thermal
- This string is the date on which the grating was thermal cycled.
- xgef
- This string is a combination of the execution date code and
X-GEF test procedure of the most recent (usually only)
X-GEF test on this grating.
Installation Columns
These columns provide information about the installation of the
grating onto the HESS.
- hessloc
- This string is the HESS location code "shell-sector-number".
- hessdate
- This string is the date on which the grating was installed
onto the HESS, generally by Bob Laliberte.
- hessangle
- This value in arc minutes is the PEM-alignement-system
measured roll-error of the grating
line angle; these small values are due to Dick Elder's finesse.
- comment
- This string is a catch-all field for terse test comments.
- whichhess
- This string is "Flight" for gratings installed on the flight HETG.
- nofly
- This string was used to indicate conditions of the grating that
prohibited its use as a flight grating.
LR Summary Columns
These columns summarize some key results of the gratings final
LR test before HESS installation.
- lrpave
- This value is the average period of the grating in
"NIST-absolute Angstroms".
The average is over an "active region" roughly representative of
the region illuminated by the HRMA: a 13.45 mm wide region for the
MEGs and a 10.03 mm wide region for the HEGs (~dd/idl/lr/gs_lr_pspec.pro).
- lrdpop
- This value is the rms fractional variation of the grating period over the
"active region" (see lrpave above). It is in units of ppm, i.e., x10-6.
- lrvalidfrac
- This value (between 0. and 1.) gives the fraction of the LR data points
(over the whole LR-tested area) which have valid measurements.
- lrmacver
- This string (e.g., "LR3.23") gives the version of the LR measurement
system for this most recent LR test of the grating.
- lrrollrms
- This value is the facet rms grating-line roll variation
in arc seconds, averaged over the full LR-tested area.
X-GEF Summary Columns
These columns provide some summary information about the grating's
X-GEF diffraction efficiency test analysis.
- xgef (this appears earlier in the column order)
- This string is a combination of the execution date code and
X-GEF test procedure of the most recent (usually only)
X-GEF test on this grating.
- xgefdir
- This string is the MIT-local directory where the X-GEF data
were analyzed and results produced for the facet-test. A prefix
of "/nfs/" yields the original full path name.
- xgefthk
- This value is an approximate thickness (height) of the roughly trapezoidal
grating bar shape - averaged over the several X-GEF tested regions
of the facet. It is in Angstroms.
- xgefline
- This value is an approximate bar-width (FWHM) of the roughly trapezoidal
grating bar shape - averaged over the several X-GEF tested regions
of the facet. It is in Angstroms.
- xgef1kev,
xgef4kev,
xgef8kev
- These three values are the average, modeled, combined +/- first-orders
facet diffraction efficiency at the three energies 1, 4, and 8 keV.
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