bunched_beam

• type: setup command.
• function: set up for tracking of particle coordinates with various distributions.

&bunched_beam
    STRING bunch = NULL;
    long n_particles_per_bunch = 1;
    double time_start = 0;
    STRING matched_to_cell = NULL;
    double emit_x  = 0;
    double emit_nx  = 0;
    double beta_x  = 1.0;
    double alpha_x = 0.0;
    double eta_x   = 0.0;
    double etap_x  = 0.0;
    double emit_y  = 0;
    double emit_ny  = 0;
    double beta_y  = 1.0;
    double alpha_y = 0.0;
    double eta_y   = 0.0;
    double etap_y  = 0.0;
    long use_twiss_command_values = 0;
    double Po = 0.0;
    double sigma_dp = 0.0;
    double sigma_s = 0.0;
    double dp_s_coupling = 0;
    long one_random_bunch = 1;
    long symmetrize = 0;
    long limit_invariants = 0;
    long limit_in_4d = 0;
    long enforce_rms_values[3] = {0, 0, 0};
    double distribution_cutoff[3] = {2, 2, 2};
    STRING distribution_type[3] = {"gaussian","gaussian","gaussian"};
    double centroid[6] = {0.0, 0.0, 0.0, 0.0, 0.0, 0.0};
    long save_initial_coordinates = 1;
&end

• bunch -- The (incomplete) name of an SDDS file to which the phase-space coordinates of the bunches are to be written. Recommended value: ``%s.bun''.
• n_particles_per_bunch -- Number of particles in each bunch.
• time_start -- The central value of the time coordinate for the bunch.
• matched_to_cell -- The name of a beamline from which the Twiss parameters of the bunch are to be computed.
• emit_X -- RMS emittance for the X plane.
• emit_nX -- RMS normalized emittance for the X plane. Ignored if emit_X is nonzero.
• beta_X, alpha_X, eta_X, etap_X -- Twiss parameters for the X plane.
• use_twiss_command_values -- If nonzero, then the values for $\beta$, $\alpha$, $\eta$, and $\eta^\prime$ are taken from the twiss command. It is an error if no twiss command has been given.
• Po -- Central momentum of the bunch.
• sigma_dp, sigma_s -- Fractional momentum spread, ${\rm\delta}$, and bunch length. Note that sigma_s is actually the length in $\beta_z*c*t$, so that for $\beta_z«1$ the length of the bunch in time will be greater than one might expect.
• dp_s_coupling -- Specifies the coupling between s and ${\rm\delta}$, defined as ${\rm\langle s \delta \rangle/(\sigma_s\sigma_\delta)}$.
• one_random_bunch -- If non-zero, then only one random particle distribution is generated. Otherwise, a new distribution will be generated for every simulation step.
• enforce_rms_values[3] -- Flags, one for each plane, indicating whether to force the distribution to have the specified RMS properties.
• distribution_cutoff[3] -- Distribution cutoff parameters for each plane.
• distribution_type[3] -- Distribution type for each plane. May be ``gaussian'', ``hard-edge'', ``uniform-ellipse'', ``shell'', or ``dynamic-aperture''.
• limit_invariants -- If non-zero, the distribution cutoffs are applied to the invariants, rather than to the coordinates.
• limit_in_4d -- If non-zero, then the transverse distribution is taken to be a 4-d gaussian or uniform distribution. One of these must be chosen using the distribution_type control. It must be the same for x and y.
• symmetrize -- If non-zero, the distribution is symmetric under changes of sign in the coordinates. Automatically results in a zero centroid for all coordinates.
• centroid[6] -- Centroid offsets for each of the six coordinates.
• 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 regenerated each time they are needed. This is more memory efficient and is useful for tracking very large numbers of particles.