BEAMAXES

defines the axes used for a beam reference frame different from the geometry frame

See also BEAM, BEAMPOS, POLARIZAti, SOURCE, SPECSOUR

     WHAT(1) = cosine of the angle between the x-axis of the beam reference
               frame and the x-axis of the geometry frame
               Default: no default

     WHAT(2) = cosine of the angle between the x-axis of the beam reference
               frame and the y-axis of the geometry frame
               Default: no default

     WHAT(3) = cosine of the angle between the x-axis of the beam reference
               frame and the z-axis of the geometry frame
               Default: no default

     WHAT(4) = cosine of the angle between the z-axis of the beam reference
               frame and the x-axis of the geometry frame
               Default: no default

     WHAT(5) = cosine of the angle between the z-axis of the beam reference
               frame and the y-axis of the geometry frame
               Default: no default

     WHAT(6) = cosine of the angle between the z-axis of the beam reference
               frame and the z-axis of the geometry frame
               Default: no default

     SDUM    : not used

     Default (option BEAMAXES not requested): the beam frame coincides with the
             geometry frame

Notes:

1) Option BEAM describes a simple pencil beam, or also a beam simply distributed in space (angular divergence and transversal profile), provided the beam axis coincides with the z-axis of the input geometry. Also a possible beam polarisation described by option POLARIZAti refers to a beam with its axis coinciding with the geometry z-axis. The purpose of option BEAMAXES is to allow the user to define angular divergence, transversal profile and polarisation for a beam of arbitrary direction, either constant as defined by option BEAMPOS, or not necessarily known in advance as provided by a user SOURCE routine. For this purpose, the user can define divergence, profile and polarisation in a beam reference frame. Option BEAMAXES establishes the correspondence between beam and geometry reference frame.

2) The origin of the beam reference frame coincides always with that of the geometry frame.

3) The user needs to input only the direction cosines of the x- and of the z-axis of the beam frame. The direction of the y-axis is determined by the program as the vector product z X x.

4) If the the x- and z-axes defined with BEAMAXES are not exactly perpendicular (in double precision!) the program forces perpendicularity by adjusting the cosines of the x-axis.

5) The direction cosines of the x- and z-axes do not need to be exactly normalised to 1. The code takes care of properly normalising all cosines.

Example:

 *  The next option cards describe a 10 GeV proton beam with a divergence of
 *  50 mrad and a gaussian profile in the "beam x"-direction and in the
 *  "beam y"-direction described by standard deviations sigma_x = 1. cm
 *  (FWHM = 2.36 cm) and sigma_y = 0.5 cm (FWHM = 1.18 cm). The beam starts
 *  from point (0,0,0) and is directed in a direction perpendicular to the
 *  "geometry x" axis, at 45 degrees with respect to both "geometry y" and
 *  "geometry z". The "beam x" axis has cosines 1,0,0 and the "beam z"
 *  axis has cosines 0, cos(pi/4), cos(pi/4)
 *...+....1....+....2....+....3....+....4....+....5....+....6....+....7....+....8
 BEAM           -10.0       0.0      50.0     -2.36     -1.18      1.0 PROTON
 BEAMPOS          0.0       0.0       0.0       0.0 0.7071068       0.0
 BEAMAXES         1.0       0.0       0.0       0.0 0.7071068 0.7071068

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