Module Precession Field

# VITESS Module Precession Field

This module simulates spin precessions in an imhomogeneous field given by an external field map file or in a homogeneous field defined by its size and the magnetic strength vectors. The spin precessions are treated classically i.e. this module only rotates the spin vectors belonging to trajectories which pass through the rectangular geometry. No attenuation is considered during the flight.

Module parameters:

Parameter Unit | Description | Command option
field map file | data file giving the field map which is read in externally | -P
Field options | option of magnetic field (1:inhomogeneous, 'else': homogeneous) | -O
position main X,Y,Z [cm] | center position of the field map | -k, -l, -m
offset horiz./vert. [deg] | horizontal (first rotation) and vertical rotation angles of the field map | -i, -j
output X,Y,Z [cm] | position of the output frame (in the input frame) | -p, -r, -s
dimension field X,Y,Z [cm] | dimension of the precession volume | -X, -Y, -V
magnetic field X,Y,Z [Oe] | components of the magnetic field in Oe | -T, -G, -H

Important note: In case of serious memory limits (mainly older computers) it is possible to get "couldn't execute "...\MODULES\precessionfield.exe": invalid argument". This is because the field resolution has to be high enough. Set "#define FIELD_SIZE 75" smaller and recompile.

Module file input:

The field map file has to be defined as below in order to obtain the proper format:

(...)
/* print number of matrix lines, columns */

fprintf(FieldMapFile, " %d %d %d\n", i_x_max, i_y_max, i_z_max) ;

(...)
/* inhomogeneous fieldsph */

{

for(i_x=1;i_x<(i_x_max+1);i_x++) { for(i_y=1;i_y<(i_y_max+1);i_y++) { for(i_z=1;i_z<(i_z_max+1);i_z++) {

(...)
/* generate field vectors in spherical representation */

(...)
/* print out to file */

fprintf(FieldMapFile, " %f %f %f %f %f %f %f %f %f \n",

Posit[0], Posit[1], Posit[2],

Dim[0], Dim[1], Dim[2],

fieldsph[0], fieldsph[1], fieldsph[2]);
}}}

}

That is, in a simplest example, a 2x2x2 homogeneous field map file could look like:

2 2 2
-2.500000 -2.500000 -2.500000 5.000000 5.000000 5.000000 1.000000 0.000000 0.000000
-2.500000 -2.500000 2.500000 5.000000 5.000000 5.000000 1.000000 0.000000 0.000000
-2.500000 2.500000 -2.500000 5.000000 5.000000 5.000000 1.000000 0.000000 0.000000
-2.500000 2.500000 2.500000 5.000000 5.000000 5.000000 1.000000 0.000000 0.000000
2.500000 -2.500000 -2.500000 5.000000 5.000000 5.000000 1.000000 0.000000 0.000000
2.500000 -2.500000 2.500000 5.000000 5.000000 5.000000 1.000000 0.000000 0.000000
2.500000 2.500000 -2.500000 5.000000 5.000000 5.000000 1.000000 0.000000 0.000000
2.500000 2.500000 2.500000 5.000000 5.000000 5.000000 1.000000 0.000000 0.000000

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Last modified: Mon Jul 22 15:36:29 MEST 2002, G. Zs.