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The Radiation Description File

Similar to the external beam description file, a file can be used to defined the seeding radiation field in form of a look-up table. The filename is specified by the RADFILE parameter. The keywords VERSION, REVERSE, and SIZE are identical to the one in the beam description file.

When the version is set to 1.0 or higher, Genesis 1.3 allows for a more flexible input and the definition of the input set, using the COLUMNS keyword. The number of allowed columns is less than for the beam description file. Parameters, which are not defined in RADFILE are filled with their value in the main input file. The list of allowed input parameters are:

  • ZPOS or TPOS
  • PRAD0

The input parameter PHASE is the radiation phase at that position and has no equivalent in the main input deck. The default value is 0. Because Genesis 1.3 samples the radiaiton field with a reference wavelength XLAMDS a linear change in PHASE correspond to a shift in the input frequency, while a quadratic dependence describes a linear chirp. Still Genesis fills the slices with a fundamental Gaussian mode. If higher modes are desired the user has to creat his own distribution on a grid and import them with the FIELDFILE option.

A new keyword is OFFSET allows to shift the radiaiton field with respect to the electron beam. The value is the offset in meters. Note that for version 1.0 and higher, Genesis 1.3 alligns first the defined input range so that the first line in the look-up table is at zero of the internal, co-moving coordinate system.