sdds_beam

• type: setup command.
• function: set up for tracking of particle coordinates stored in an SDDS file.

&sdds_beam
    STRING input = NULL;
    STRING input_type = "elegant";
    long n_particles_per_ring = 0;
    STRING selection_parameter = NULL;
    STRING selection_string = NULL;
    long one_random_bunch = 0;
    long reuse_bunch = 0;
    long prebunched = 0;
    long sample_interval = 1;
    long n_tables_to_skip = 0;
    long center_transversely = 0;
    long center_arrival_time = 0;
    double sample_fraction = 1;
    double p_lower = 0.0;
    double p_upper = 0.0;
    long save_initial_coordinates = 1;
&end

• input -- Name of an SDDS file containing coordinates of input particles.
• input_type -- May be ``elegant'' or ``spiffe'', indicating the name of the program that wrote the input file. The expected data quantities for the different types are:
  • elegant: ${\rm (x, xp, y, yp, t, p)}$, where x and y are in meters, ${\rm xp=x^\prime}$ and ${\rm xp=y^\prime}$ are dimensionless, t is in seconds, and ${\rm p=\beta\gamma}$ is the dimensionless momentum.
  • spiffe: ${\rm (r, z, pr, pz, t)}$, where r and z are in meters, ${\rm pr=\beta_r \gamma}$, ${\rm pz = \beta_z \gamma}$, and t is in seconds.
• n_particles_per_ring -- For spiffe data, gives the number of particles to generate for each ring of charge.
• selection_parameter -- The name of a parameter in the SDDS file to be used for selection of pages of data.
• selection_string -- The value of the selection_parameter selection parameter required for a page to be used. E.g., if you have a file from the shower program containing positrons, electrons, and photons, you might want to select only the positrons.
• one_random_bunch -- A flag indicating whether, for spiffe data, a new random distribution should be calculated for each step of the simulation.
• prebunched -- A flag indicating, if zero, that the entire file is one ``bunch,'' and otherwise that each page in the file is a different bunch.
• sample_interval -- If non-zero, only every sample_interval$^{\rm th}$ particle is used.
• n_tables_to_skip -- Number of SDDS pages to skip at the beginning of the file.
• center_transversely -- If non-zero, the transverse centroids of the distribution are made to be zero.
• center_arrival_time -- If non-zero, the mean arrival time of particles at the start of the accelerator is set to zero.
• sample_fraction -- If non-unity, the randomly selected fraction of the distribution to use.
• p_lower, p_upper -- If different, the lower and upper limit on ${\rm\beta\gamma}$ of particles to use.
• save_initial_coordinates -- A flag that, if set, results in saving initial coordinates of tracked particles in memory. This is the default behavior. If unset, the initial coordinates are not saved, but are reread from disk each time they are needed. This is more memory efficient and is useful for tracking very large numbers of particles.