4.9 load_particles

• description:

  Allows loading particles from an SDDS file. This is an alternative to using a cathode and can provide essentially arbitrary particle distributions. Since spiffe is a 2.5 dimensional code, the “particles” are really rings at a given radius and longitudinal position.

  Note that particles can be injected into the simulation region if they start with z or r coordinates outside of z : [z_min,z_max] or r : [0,r_max]. In this case, the particles drift ballistically until they enter the problem region. As a special case, particles entering from the left-hand side of the problem region are not active until they emerge from any metal surface that abuts z = z_min.

• example:
  &load_particles  
      filename = "particles.sdds",  
  &end

  This loads particles from the file particles.sdds.

• synopsis and defaults:
  #namelist load_particles  
          STRING filename = NULL;  
          long sample_interval = 1;  
          double stiffness = 1;  
  #end

• details:
  • filename: Name of the SDDS file from which to take particle data. The file must have the following columns with the following units:
    • : longitudinal position in meters.
    • : radial poition in meters. If the particle position is initially outside the problem region or inside a metal volume, it will move ballistically until it enters the problem region or emerges from the metal.
    • : longitudinal momentum, β_zγ.
    • : radial momentum, β_rγ.
    • : azimuthal momentum, β_ϕγ.
    • : charge, in Coulombs.
  • sample_interval: Causes spiffe to take only every sample_interval^th particle from the file.
  • stiffness: Allows making the beam artificially stiff. Equivalent to increasing the particle mass by the given factor.