Longitudinal wake specified as a function of time lag behind the particle.
Parallel capable? : yes
GPU capable? : yes
Back-tracking capable? : yes
name of file giving Green function
column in INPUTFILE containing time data
column in INPUTFILE containing Green function
beam charge (or use CHARGE element)
factor by which to multiply wake
number of bins for current histogram
Use Savitzky-Golay filter to smooth current histogram?
Savitzky-Golay filter half-width for smoothing
Savitzky-Golay filter order for smoothing
change central momentum?
allow beam longer than wake data?
Number of passes over which to linearly ramp up the wake to full strength.
If non-zero, then do calculations bunch-by-bunch.
If non-zero, then an acausal wake is allowed.
Optionally used to assign an element to a group, with a user-defined name. Group names will appear in the parameter output file in the column ElementGroup
The input file for this element gives the longitudinal Green function, W(t) versus time behind the particle. The units of the wake are V/C, so this element simulates the integrated wake of some structure (e.g., a cell or series of cells). If you have, for example, the wake for a cell and you need the wake for N cells, then you may use the FACTOR parameter to make the appropriate multiplication. The values of the time coordinate should begin at 0 and be equi-spaced, and be expressed in seconds. A positive value of time represents the distance behind the exciting particle.
A positive value of W(t) results in energy loss. A physical wake function should be positive at t = 0. Causality requires that W(t) = 0 for t < 0. Acasual wakes are supported, provided the user sets ACAUSAL_ALLOWED=0. The data file must contain a value of W(t) at t = 0, and should have equal spans of time to the negative and positive side of t = 0.
Use of the CHARGE parameter on the WAKE element is disparaged. It is preferred to use the CHARGE element as part of your beamline to define the charge.
Setting the N_BINS paramater to 0 is recommended. This results in auto-scaling of the number of bins to accomodate the beam. The bin size is fixed by the spacing of the time points in the wake.
The default degree of smoothing (SG_HALFWIDTH=4) may be excessive. It is suggested that users vary this parameter to verify that results are reliable if smoothing is employed (SMOOTHING=1).
The algorithm for the wake element is as follows:
Bunched-mode application of the short-range wake is possible using specially-prepared input beams. See Section 6 for details. The use of bunched mode for any particular WAKE element is controlled using the BUNCHED_BEAM_MODE parameter.