description: Computes the steady-state CSR impedance with shielding by parallel plates.
By default, the computed impedance is for a dipole magnet that bends the beam in a complete
circle.
outputFile — SDDS file containing computed impedance. May be used directly with
elegant’s ZLONGIT element.
switches:
-height — The full height of the vacuum chamber, in meters.
-radius — The radius of the bending magnet, in meters.
-angle — The angle of the bending magnet, in radians. The default is 2π.
frequencyLimit — Allows specifying the upper frequency limit (required), as well as
the lower frequency limit, for the computed impedance. elegant will not accept the data
if the lower limit is not 0. If the rms bunch length is σt, then it is suggested to have the
maximum frequency much greater than 1∕sigmat.
-n — Allows specifying the number of data points to be computed. The number of points
computed is 2n+ 1, which is required by elegant. A reasonable value is n = 10 to
n = 14.
-filter — Allows specifying the starting and ending frequency for a simple low-pass
filter. The frequencies are given as fractions of the maximum frequency. The filter ramps
linearly from 1 to 0 between the two cutoff values. If, for example, the cutoff is 0.2,
then the highest frequency for which the impedance is unmodified corresponds to a
wavelength of 10 bins (2∕0.2) in elegant. The intention of this feature is to provide a
way to taper the impedance down to reduce high-frequency noise; another option is to
apply a gaussian filter externally, e.g., using sddsprocess.
authors: Y. Wang, H. Shang, ANL/APS. Based on a simplified form[39] of Warnock’s [40]
formula.
Note: The script makeSummedCsrZ is more convenient for computing the CSR impedance of rings
with several types of dipoles, and also handles the free-space case.