7.16 closed_orbit

• type: setup/action command.
• function: set up for computation of the closed orbit.
• Command syntax, including use of equations and subcommands, is discussed in 7.2.

• output — The (incomplete) name of an SDDS file to which the closed orbits will be written. Recommended value: “%s.clo”.
• output_monitors_only — If non-zero, indicates that the closed orbit output should include only the data at the locations of the beam-position monitors.
• start_from_centroid — A flag indicating whether to force the computation to start from the centroids of the beam distribution.
• start_from_dp_centroid — A flag indicating whether to force the computation to use the momentum centroid of the beam for the closed orbit. This can allow computing the closed orbit for an off-momentum beam, then starting the beam on that orbit using the offset_by_orbit or center_on_orbit parameters of the track command. In contrast to the start_from_centroid, this command doesn’t force the algorithm to start from the beam transverse centroids.
• closed_orbit_accuracy — The desired accuracy of the closed orbit, in terms of the difference between the start and end coordinates, in meters. Iteration will terminate when this value is achieved.
• closed_orbit_accuracy_requirement — The required accuracy of the closed orbit. If not achieved, the closed orbit calculation is considered to have failed.
• closed_orbit_iterations — The number of iterations to take in finding the closed orbit.
• iteration_fraction — Fraction of computed change that is used each iteration. For lattices that are very nonlinear or close to unstable, a number less than 1 can be helpful. Otherwise, it only slows the simulation.
• fixed_length — A flag indicating whether to find a closed orbit with the same length as the design orbit by changing the momentum offset.
• start_from_recirc — A flag indicating whether to compute the closed orbit from the recirculation (recirc) element in the beamline. In general, if one has a recirculation element, one should give this flag.
• verbosity — A larger value results in more printouts during the computations.
• iteration_fraction — Controls the fraction of the update to apply when iterating toward a closed orbit. Smaller numbers give less chance of instability at the price of slower convergence.e
• fraction_multiplier — Multiplier to apply to the iteration fraction if iteration is converging.
• multiplier_interval — Interval in number of iterations at which to adjust the iteration fraction.
• output_monitors_only — If non-zero, output file contains data only at beam position monitors, i.e., at MONI, HMON, and VMON elements.
• tracking_turns — If non-zero, the number of turns to track for detemination of the closed orbit by averaging. This may be useful if the regular closed orbit algorithm complains about convergence issues.
• disable — If non-zero, disables the command.
• immediate — If non-zero, computations are done immediately, so the command acts as an action command.