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POLARIZAti

defines the polarisation of a photon beam or source and activates transport of polarised photons

     WHAT(1) <= 1.0: x-axis cosine of the beam polarisation vector (electric
                     vector in case of photons)
    |WHAT(1)| > 1.0: resets the default (no polarisation)
               This value can be overridden in user routine SOURCE
               by assigning a value to variable UBMPOL
               Default = -2.0 (no polarisation)

     WHAT(2) = y-axis cosine of the beam polarisation vector
               This value can be overridden in user routine SOURCE
               by assigning a value to variable VBMPOL
               Default = -2.0 (no polarisation)
               Default = 0.0

     WHAT(3) = z-axis cosine of the beam polarisation vector
               This value can be overridden in user routine SOURCE
               by assigning a value to variable WBMPOL
               Default = -2.0 (no polarisation)
               Default = 0.0

     WHAT(4) : flag for relative direction of beam and polarisation
             >= 1.0: the polarisation is orthogonal to the direction of
                     the primary photons
              < 1.0: resets the default (polarisation not orthogonal to
                     the direction of primaries)
               This value can be overridden in user routine SOURCE
               by assigning a value to the logical variable LPPERP
               Default = 0.0 (the polarisation is not orthogonal to the
               direction of the primaries)

     WHAT(5) = polarisation fraction (see explanation in WHAT(6) below)
             < 0.0: resets the default = 1.0
             > 1.0: resets the default = 1.0
               This value can be overridden in user routine SOURCE
               by assigning a value to variable POLFRA
               Default = 1.0 (fully polarised in the direction described
               by WHAT(1,2,3)

     WHAT(6)   : flag for interpreting WHAT(5):
        =< 0.0 : a fraction |WHAT(5)| of beam particles are linearly
                 polarised in the direction described by WHAT(1,2,3) and
                 the remaining fraction (1 - WHAT(5)) are not polarised
        >= 1.0 : a fraction WHAT(5) of beam particles are linearly
                 polarised in the direction described by WHAT(1,2,3) and
                 the remaining fraction (1 - WHAT(5)) are polarised in
                 the direction orthogonal to both the beam and
                 that described by WHAT(1,2,3)
                 This value can be overridden in user routine SOURCE
                 by assigning a value to the logical variable LPFRAC
                 Default = 0.0 (only a fraction WHAT(5) of the photons is
                 polarised as indicated by WHAT(1,2,3), and the remaining
                 fraction is not polarised)

     SDUM :    not used

     Default (option POLARIZAti not given): photons are not assumed to be
             polarised

Notes:

• 1) The program takes care of properly normalising the cosines unless they are badly unnormalised (in the latter case the code would reset to no polarisation). If WHAT(4) >= 1.0, the code makes sure that the two vectors are orthogonal within the minimum possible rounding errors.

• 2) What polarisation means is dependent on the physics implemented in the code: for the moment the only polarisation dependent effects are Compton, Rayleigh and photoelectric for photons, where of course the polarisation vector represents the electric field direction and must be normal to the beam direction.

Example:

 * Synchrotron radiation beam with m_e/E mrad x,y divergence (produced by a 3 GeV
 * electron beam). The actual spectrum is provided by a a user-written source
 * (E_max = 500 keV). Photons are fully polarised in the horizontal (y) direction
 * and the polarisation is orthogonal to the direction of the primary photons
 *...+....1....+....2....+....3....+....4....+....5....+....6....+....7....+....8
 DEFAULTS                                                              EM-CASCA
 BEAM        -500.E-6       0.0 1.7033E-4       0.0       0.0       1.0PHOTON
 SOURCE           0.0       0.0       0.0       0.0       0.0       0.0
 POLARIZA         0.0       1.0       0.0       1.0       1.0       0.0