Program name: ebrt.pro
Program directory: ~dd/irt/ebrt
Program Language: IDL with IRT ray-trace routines

Program brief description:

	This program ray traces a faceted HETG with idealized HRMA and
has error terms identical to those in the (Mac Excel) error budget.
The various error terms are in the array eb_Ps (error budget
parameters) and can be referenced by spreadsheet line number (e.g.
HRMA blur = eb_Ps(7) ) or by error budget symbol ( eb_Ps(eb_B) ) with
"eb_" scattered about.  The error budget terms that are currently
implemented are:

		Error Budget / Ray Trace Terms

	 #	Description			Symbol	Units
  
	--	Energy				eb_EkeV	(keV)
	15	Finite Facet size		eb_L	mm
	16	Detector defocus		eb_fD	mm
	17	Detector tilt			eb_tD	arc minutes
	18	Plate radius error
		   HETG-focus dist		eb_X	mm
		   HETG Rowland dia.		eb_XRC	mm
	25	Facet-facet period var		eb_dppB	(x10-4)
	28	Facet tilt (perp to lines)	eb_aM	arc minutes
	29	Facet tilt (parallel to lines)	eb_bM	arc minutes
	40	Plate decenter (perp.)		eb_u1PH	mm
	41	Plate decenter (parall.)	eb_u2PH	mm
	42	Plate defocus			eb_vPH	mm
	43	Plate tilt (perp to lines)	eb_e1PH	arc minutes
	44	Plate tilt (perp to lines)	eb_e1PH	arc minutes


Program operation/example:

	cd ~dd/irt/ebrt
	s_idl			(only needed once per window login)
	idl
(The error budget parameters are reset to 0 and the IDL prompt appears:
		 Reset to MEG parameters
		IRT,ebrt>                    )
	ebrt			(this runs the program)
(The output of the program is a "spot" cross section of the rays as they
hit a plane detector located at the correct axial location to be on the
Rowland circle (for detector defocus and tilt = 0).  In addition the
error budget generated values are calculated and output for comparison
with the ray-trace.)

(The cross section can be viewed at different axial locations by using
the movez command, e.g.:)
	movez, 2.0		(the 2.0 is a 2 mm delta-position)
(A parameter can be modified and a new ray-trace done:)
	eb_Ps(eb_dppB) = 2.5
	ebrt
(Hard copy output can be made by typing:)
	pre_print		(changes graphics output to postscript)
	movez, 0.		(replots the spot pattern to .ps file)
	post_print		(send .ps file to laser printer)


Other features:

	This s/w contains an IDL version of the Mac error budget
(eb_update.pro does the calculations); this error budget itself can be
evaluated and plotted vs energy by typing "eb_vse".  The current values
of the eb_Ps are used as input parameters.
	The error budget parameters (eb_Ps) are initially set to 0 and
also set for the MEG values (e.g., grating period).  HEG parameters
with zero-errors can be set with "eb_resetforrt,0" (reset for
ray-tracing; replace the 0 with 1 for MEG values.)  To set all
(realistic) errors use "eb_reset, 0" (or 1 for MEG).  The eb_vse.pro can
be edited to include an energy-dependant HRMA blur in the error budget
calculations.  "eb_dump" types out a complete list of the error budget
for term-by-term comparison with the Mac version (they should agree
because it's the same equations...).