&coupled_twiss_output STRING filename = NULL; long output_at_each_step = 0; long emittances_from_twiss_command = 1; double emit_x = 0; double emittance_ratio = 0.01; double sigma_dp = 0; long calculate_3d_coupling = 1; long verbosity = 0; long concat_order = 2; &end
filename-- The (incomplete) name of the SDDS file to which coupled twiss parameters and beam sizes will be written. Suggested value: ``%s.ctwi''.
output_at_each_step-- If nonzero, then this is a setup command and results in computations occurring for each simulation step (e.g., for each perturbed machine if errors are included). If zero, then this is an action command and computations are done immediately (e.g., for the unperturbed machine). If you wish to compute Twiss parameters on a closed orbit or after other calculations, be sure to set this control to a nonzero value.
emittances_from_twiss_command-- If nonzero, then the values of the horizontal emittance and the momentum spread are taken from the uncoupled computation done with the
twiss_outputcommand. In this case, the user must issue a
twiss_outputcommand prior to the
coupled_twiss_output. If zero, then the values of the horizontal emittance and the momentum spread are taken from the parameters
emit_x-- Gives the horizontal emittance, if
emittance_ratio-- Gives the ratio of the x and y emittances. Used to determine the vertical emittance from the horizontal emittance. Note that the computation is not self-consistent. I.e., the user is free to enter any emittance ratio desired, whether it is consistent with the machine optics or now.
sigma_dp-- Gives the momentum spread, if
This feature was added to elegant using code supplied by V. Sajaev, based on Ripkin's method. The code computes the coupled lattice functions, then uses the supplied emittance, emittance ratio, and momentum spread to compute the beam sizes, bunch length (if rf is included), and beam tilt.