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Date: Mon, 13 May 91 17:57:15 -0600
From: cash@cygx3.colorado.edu (Webster Cash)
Message-Id: <9105132357.AA28134@cygx3.colorado.edu>
To: dd
Subject: Explanation of Software
Status: R


    HETG SIMULATION SOFTWARE

    DEVELOPED FOR MIT, CENTER FOR SPACE RESEARCH

    MAY 1991



    By:  Parsec Technology
         (303)-447-0071

         attn: Webster Cash
         (303)-492-4056



  This is a package of raytrace procedures is designed to function as part
of Interactive Raytrace (IRT) version 2.7.  It simulates the performance of
the High Energy Transmission Gratings (HETG) on AXAF.  It can be used to
analyze and verify the design, create simulated fields of view, and set parameters
and tolerances for the design.

  There are a total of nine procedures which support four independent raytyrace
paths.

1)  hfull.pro -> hetgfull.pro -> acis.pro

  hfull.pro is the full simulation that calls all of the miniature grating elements
in a giant multipath loop.  This is the routine that can be used to set tolerances
and detailed grating specs for HETG.  It is, unfortunately, somewhat slow in that
it involves a fair amount of disk useage.

  hfull.pro sets recap to zero so that plotrays will not work at the end.  The
recap matrix grows too large for core with the hundreds of elements.  If a
plotrays output is needed use tg.pro instead.

2)  tg.pro -> torgrathetg.pro -> acis.pro

  This is a quick and dirty version that allows the user to trace an excellent
approximation to HETG without the slow and cumbersome multipath used in hfull.pro.
The approximation is to use the ideal geometry as described by Beuermann et al.
It is, essentially, the HETG in the limit of vanishingly small element size.


3)  tgh.pro -> torgrath.pro -> acis.pro

  This is the same as tg.pro, but it vignettes the rays from the outer three
HRMA nests, so the user may investigate the aberrations from the high energy
grating alone.


4)  tgm.pro -> torgratm.pro -> acis.pro 


  Same as for tgh.pro, but for the medium energy grating.


*************************************************************

  SYSTEM VARIABLES

  In developing these simulation routines several variables have been defined
for the convenience of the user.

nr      ---   the number of rays to be traced per wavelength
wav     ---   wavelength to be traced.  May to single or vector.
nord    ---   diffraction order to be traced.
tolhetg ---   tolerance toggle.  For use with hfull.pro only.
                  This is usually tolon, but because tolon
                  is set to 1 for the HRMA, tolhetg allows the user to
                  perform tolerance on the HETG independently.  Set tolhetg
                  to 1 for tolerancing of the array as a whole.  Set tolhetg
                  to 2 to perform monte carlo tolerancing of the element set.
                  For tolerancing with tg.pro use tolon as usual.