&twiss_output STRING filename = NULL; long matched = 1; long output_at_each_step = 0; long output_before_tune_correction = 0; long final_values_only = 0; long statistics = 0; long radiation_integrals = 0; long concat_order = 3; long higher_order_chromaticity = 0; long higher_order_chromaticity_points = 5; double higher_order_chromaticity_range = 4e-4; double chromatic_tune_spread_half_range = 0; long quick_higher_order_chromaticity = 0; double beta_x = 1; double alpha_x = 0; double eta_x = 0; double etap_x = 0; double beta_y = 1; double alpha_y = 0; double eta_y = 0; double etap_y = 0; STRING reference_file = NULL; STRING reference_element = NULL; long reference_element_occurrence = 0; long reflect_reference_values = 0; long cavities_are_drifts_if_matched = 1; long compute_driving_terms = 0; long leading_order_driving_terms_only = 0; long local_dispersion = 1; &end
filename-- The (incomplete) name of an SDDS file to which the Twiss parameters will be written. Recommended value: ``%s.twi''.
matched-- A flag indicating, if set, that the periodic or matched Twiss parameters should be found.
output_at_each_step-- A flag indicating, if set, that output is desired at each step of the simulation.
output_before_tune_correction-- A flag indicating, if set, that output is desired both before and after tune correction.
final_values_only-- A flag indicating, if set, that only the final values of the Twiss parameters should be output, and not the parameters as a function of s.
statistics-- A flag indicating, if set, that minimum, maximum, and average values of Twiss parameters should be computed and included in output.
radiation_integrals-- A flag indicating, if set, that radiation integrals should be computed and included in output. N.B.: Radiation integral computation is not correct for systems with vertical bending, nor does it take into account coupling. See the
moments_outputcommand if you need such computations.
matchedis zero, the initial values for the X plane.
concat_order-- Order of matrix concatenation to use for determining matrix for computation of Twiss parameters. Using a lower order will result in inaccuracy for nonlinear lattices with orbits and/or momentum errors. However, for on-momentum conditions with zero orbit, it is much faster to use
higher_order_chromaticity-- If nonzero, requests computation of the second- and third-order chromaticity. To obtain reliable values, the user should use
concat_order=3in this namelist and the highest available order for all beamline elements. elegant computes the higher-order chromaticity by finding the trace of off-momentum matrices obtained by concantenation of the matrix for
higher_order_chromaticity_pointsvalues of over the full range
quick_higher_order_chromaticityis nonzero, then a quicker concatenation method is used that gives the second-order chromaticity only.
chromatic_tune_spread_half_range-- Half range of for which the chromatic tune spread is computed. The results are available in for optimization and in the twiss output file under the names
nuxChromLower, and similarly for the y plane. This computation uses the chromaticities.
reference_file-- If given, the name of a file from which twiss parameter data will be taken to give the starting values. Ignored if
matchedis nonzero. The file should have the beta and alpha functions with the same names as the file created by this command.
reference_element-- Element in
reference_fileat which to take the twiss parameter values. If not given, the values at the last element in
reference_element_occurrence-- Ignored if
reference_elementis not given. Otherwise, the occurence number of
reference_elementto use. If 0, the last occurence is used.
reflect_reference_values-- If nonzero, reference values of and are multiplied by -1. This permits matching backwards from the reference point.
cavities_are_drifts_if_matched-- By default, if
matched=1, elegant treats rf cavities as drift spaces, allowing the user to have a cavity in the ring definition without it affecting the lattice functions. By setting
cavities_are_drifts_if_matched=0, one can force elegant to use the actual matrix for the rf cavity. The differences between the results are generally small, but the default behavior disagrees with the results of
moments_output. This feature is not available for cavities that change the beam energy (
CHANGE_P0=1in element definition or
compute_driving_terms-- If nonzero, then resonance driving terms [29,36,37] and tune shifts with amplitude are computed by summing over dipole, quadrupole, sextupole, and octupole elements. For dipoles, only the effects of gradients and sextupole terms are included; curvature effects are not present in the theory. In addition, these quantities may be optimized by using those names in optimization terms (see list below).
leading_order_driving_terms_only-- If nonzero, only the leading order driving terms are computed. I.e., terms involving double sums over sextupole and quadrupole strengths are not computed. However, leading-order octupole terms are computed, even though they affect the same terms as the second-order sextupole and quadrupole terms. This option is provided because computing the higher-order terms is time-consuming and not always worthwhile.
local_dispersion-- Normally, elegant will ignore acceleration in computing the dispersion. That is, the dispersion would be the ``local'' dispersion , where was the local fractional momentum deviation. In a linac or other systems with rf elements, one might also be interested in the ``global'' dispersion , where is the energy deviation at the beginning of the system. In this case, set
local_dispersion=0. Alternatively, one may look at the elements of the matrix from
The output file from this command contains the following columns, giving values of quantities at the exit of each element, unless otherwise noted.
The output file contains the following parameters. Note that chromatic quantities depend on the order
settings of the individual elements, the default order (in
run_setup), and the concatenation order
given in the
twiss_output command. These quantities pertain to the end of the lattice or to the
lattice as a whole.
tune_shift_with_amplitudecommand is given.
compute_driving_termsis nonzero. See table 2 for an explanation of each term.
tune_shift_with_amplitudefor discussion and comparison with dnux/dAx etc. These will be zero unless
N.B.: the higher-order dispersion and higher-order chromaticity are computed using the concatenated third-order matrix. However, elegant only has third-order matrices for three elements: alpha magnets, quadrupoles, and sextupoles. This may be acceptable if any dipoles (for example) have large bending radius. Users who are concerned about these effects should perform off-energy tracking using canonical elements (i.e., CSBEND, KQUAD, KSEXT, and MULT), which include energy dependence to all orders.
Also, note that by default all elements are computed to second order
only. You must change the
default\_order parameter on
3 in order to use the third-order matrices
for alpha magnets, quadrupoles, and sextupoles. You may also use the
ORDER parameter on individual element definitions.
|h11001||drives x chromaticity|
|h00111||drives y chromaticity|
|h20001||drives synchro-betatron resonances|
|h00201||drives momentum-dependence of beta functions|
|h10002||drives second order dispersion|