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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