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[ <--- prev -- ] [ HOME ] [ -- next ---> ] ## BEAMAXESdefines the axes used for a beam reference frame different from the
geometry frame
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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