17} Special source: synchrotron radiation

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 Synchrotron radiation as a source can be specified via command SPECSOUR and
 
SDUM
 = SYNC-RAD, SYNC-RDN, SYNC-RAS, or SYNC-RDS.
 Synchrotron radiation photons are assumed to be emitted by a particle
 (most commonly an electron or a positron, but any charged particle is allowed),
 moving along one or two circular arcs or helical paths. The emitting particle
 is not transported. The bending is assumed to be due to a magnetic field of
 intensity and direction specified by the user, but no magnet needs necessarily
 to be described in the geometry, and the magnetic field must not be declared
 with command MGNFIELD nor assigned to any region with command ASSIGNMAt.

 The program samples energy and direction of the synchrotron radiation photons
 from the proper energy and angular distributions. Polarization is implemented
 as a function of emitted photon energy. The emitting particle can have any
 direction with respect to that of the magnetic field. Therefore, photon
 emission can occur along arcs (if the particle direction is perpendicular to
 the magnetic field) or helical paths in the more general case.

 The user must specify several parameters:

 - the emitting particle type and energy (or momentum)
 - the particle direction, at the beginning of the first and possibly of the
   second arc or helical path
 - the magnetic field intensity (or alternatively the curvature radius of the
   particle trajectory)
 - the direction of the magnetic field
 - the lower limit of the photon energy spectrum
 - the length of one of the trajectory arcs or helical paths (the other path, if
   present, having the same length)
 - the starting points of the first path, and if present, of the second path


 The SPECSOUR command for synchrotron radiation extends over two cards. The
 input parameters are:

     
WHAT(1)
 = particle emitting the radiation
               
Default
: 3.0 (ELECTRON)
     
WHAT(2)
 > 0.0: emitting particle momentum (GeV/c)
             < 0.0: kinetic energy of the emitting particle (GeV)
     
WHAT(3)
 > 0.0: curvature radius of the emitting particle trajectory (cm)
             < 0.0: absolute value of the bending magnetic field (T)
     
WHAT(4)
 = lower limit of the photon energy spectrum (GeV)
               
Default
: 1.E-7 GeV
     
WHAT(5)
 = x-component of the magnetic field versor
     
WHAT(6)
 = y-component of the magnetic field versor

     
SDUM
    = SYNC-RAD if the z-component of the magnetic field versor is > 0.0

               SYNC-RDN if the z-component is < 0.0

               SYNC-RAS if the z-component of the magnetic field versor is > 0.0
               and the magnetic field of the second arc (if present) has opposed 
               sign to that of the first arc.

               SYNC-RDS if the z-component is < 0.0 and the magnetic field of 
               the second arc (if present) has opposed sign to that of the first 
               arc.

     Continuation card:

     
WHAT(1)
 = length of the emission arc or helical path (cm)
               
Default
 = 100.0 cm
     
WHAT(2)
 = x-coordinate of the starting point of a possible second path of
               same length (see Note 1)
     
WHAT(3)
 = y-coordinate of the starting point of the second path (see Note 1)
     
WHAT(4)
 = z-coordinate of the starting point of the second path (see Note 1)
     
WHAT(5)
 = x-component of the emitting particle direction versor at the
               beginning of the second path (see Notes 1 and 2)
     
WHAT(6)
 = y-component of the emitting particle direction versor at the
               beginning of the second path (see Notes 1 and 2)
     
SDUM
    = "&" in any position in columns 71-78 (or in last field if free
               format is used)

  
Note:

      1) The starting point of the first arc or helical path as well as the
         initial direction of the emitting particle must be defined in the
         BEAMPOS card.
      2) The z-component of the emmitting particle direction versor for the
         2nd arc takes the same sign as the one of the 1st arc

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