tune_shift_with_amplitude

• type: setup command.
• function: prepare for computation of tune shifts with amplitude.
• note: must be given prior to the twiss_output command.
• method: tune shifts with amplitude are computed via tracking a series of particles at different amplitudes. NAFF is used to determine the tunes from the tracking data. It is the user's responsbility to optimize the parameters to ensure that results are reasonable. Using tracking to determine tune shifts is more accurate than analytical methods as it includes multi-turn effects that are important in some rings (e.g., the APS).

&tune_shift_with_amplitude
    long turns = 1000;
    double x0 = 1e-10;
    double y0 = 1e-10;
    double x1 = 1e-6;
    double y1 = 1e-6;
    double scale_down_factor = 2;
    double scale_up_factor = 1.05;
    double scale_down_limit = 0.01;
    double scale_up_limit = 1e-5;
    long scaling_iterations = 10;
    long use_concatenation = 1;
    long verbose = 0;
&end

• turns -- The number of turns to track. If zero, then the concatenated matrix is used instead of tracking. This doesn't work well with all lattices. The order of the concatenated matrix is given by the concat_order control in twiss_output.
• x0, y0 -- The initial x and y amplitudes to use for determining the small-amplitude tunes.
• x1, y1 -- The initial x and y amplitudes to user for determining the tune shifts. These values should be small enough to ensure linearity in the tune shift. If the difference in tune is greater than 0.01, elegant will automatically reduce these initial values and iterate.
• scale_down_factor, scale_up_factor, scale_down_limit, scale_up_limit, scaling_iterations -- These control automatic scaling of the amplitudes. If elegant sees a tune shift larger than scale_down_limit it will decrease x0 (or y0) by the factor scale_down_factor. If elegant sees a tune shift smaller than scale_up_limit it will increase x0 (or y0) by the factor scale_up_factor.
• verbose -- If nonzero, information about the progress of the algorithm is printed to the screen.
• use_concatenation -- If nonzero, then tracks with the concatenated matrix instead of element-by-element. The order of the concatenated matrix is given by the concat_order control in twiss_output. The user should experiment with this option to see if the results are reliable for a particular lattice.