5.3. TAS configuration file

RESTRAX needs a number of additional parameters compared to the matrix method of Cooper&Nathans. These parameters describe in more details the TAS components and their distances. They are stored in the configuration file ( restrax46.cfg by default). RESTRAX prompts for this file upon startup, later on the CFG command can be used to update the configuration, when the *.cfg file has been modified.

A new configuration file can be generated by filling a form on the RESTRAX server.

5.3.1. Configuration file format

The file consists of a sequence of line pairs. The first line (ignored by RESTRAX) contains a header with parameter names, in the second one the parameter values are given in the corresponding order in a free number format (do not put decimal dot where integer is expected!). All dimensions are given in [cm] except of the curvatures [1/m] of guides and focusing devices.

title (max.60 characters):
sample setup for RESTRAX 4.6

This caption would appear in the printed output.

source (shape,diameter,width,height):
0  10.  8.  8.

shapecircular (0), rectangular (1) or elliptical (2)
diameterused if shape=0
width, height used if shape >=1

n-guide (use,dist,length,hor1,hor2,ver1,ver2,ro,gh,gv,refh,refv):
0  10.  6300.  2.5  2.5  5.  15.  2.4E-4   1  1  1  1

This line describes the first collimator section between source and monochromator. Together with the "collimator 1" it describes a neutron guide or an in-pile collimation system. The first parameter is an integer specifying the presence of this section (>0 yes, 0 no). The other parameters have a meaning common to all collimator components (cf. below).

monochromator (chi,aniz.,poiss.,thick.,height,length,segments H&V):
0.0  1  0.3  0.3  12.0  10.0   1  3

chicrystal cutting angle [deg], 0 for the symmetric Bragg reflection
anizratio of the vertical and horizontal mosaicity
poissPoisson number for the elastically bent crystals (usually about 0.3)
thick.,height,lengthmonochromator dimensions
segments H&Vnumber of crystal segments in horizontal and vertical direction; if the crystal is perfect (ETAM=0), only vertical segments are considered and the horizontal curvature is interpreted as elastic bending

analyzer(chi,aniz.,poiss.,thick.,height,length,segments H&V):
0.0   1   0.3   0.3   12.0  10.0   1   3

Analyzer parameters. Syntax and meaning are the same as for the monochromator.

detector (shape,diameter,width,height):
1       4.0      3.0      5.0

Detector window. Syntax and meaning are the same as for the source.

distances (l1,l2,l3,l4):
900. 210. 150. 70.

Distances between the source, monochromator, sample , analyzer and detector. If the n-guide is present, the first distance is measured from its exit, otherwise from the source.

1st collimator (dist,length,hor1,hor2,ver1,ver2,ro,gh,gv,refh,refv):
236.  534.  8.05  5.  9.05  11.  0.  0.  0 .  1  1
2nd collimator (dist,length,hor1,hor2,ver1,ver2,ro,gh,gv,refh,refv):
87.  35.  4.  4.  7.  7.  0.  0.  0.   1  1
3nd collimator (dist,length,hor1,hor2,ver1,ver2,ro,gh,gv,refh,refv):
60.  35.  4.  4.  7.  7.  0.  0.  0.   1  1
4th collimator (dist,length,hor1,hor2,ver1,ver2,ro,gh,gv,refh,refv):
35.  20.  4.  4.  12.  12.  0.  0.  0.&nbs p; 1  1

These 4 items describe the collimators between the source (after n-guide), monochromator, sample , analyzer and detector. The meaning of parameters is described in the section on collimator components.