Longitudinal wake specified as a function of time lag behind the particle.
Parallel capable? : yes
GPU capable? : yes
Backtracking capable? : yes
Parameter Name  Units  Type  Default  Description 
INPUTFILE  STRING  NULL  name of file giving Green function 

TCOLUMN  STRING  NULL  column in INPUTFILE containing time data 

WCOLUMN  STRING  NULL  column in INPUTFILE containing Green function 

CHARGE  C  double  0.0  Deprecated—use CHARGE element 
FACTOR  double  1  factor by which to multiply wake 

N_BINS  long  0  number of bins for current histogram 

INTERPOLATE  long  0  interpolate wake? 

SMOOTHING  long  0  Use SavitzkyGolay filter to smooth current histogram? 

SG_HALFWIDTH  long  4  SavitzkyGolay filter halfwidth for smoothing 

SG_ORDER  long  1  SavitzkyGolay filter order for smoothing 

CHANGE_P0  long  0  change central momentum? 

ALLOW_LONG_BEAM  long  0  allow beam longer than wake data? 

RAMP_PASSES  long  0  Number of passes over which to linearly ramp up the wake to full strength. 

BUNCHED_BEAM_MODE  long  1  If nonzero, then do calculations bunchbybunch. 

START_BUNCH  long  1  In bunched beam mode, if nonnegative, starting bunch number for computations 

END_BUNCH  long  1  In bunched beam mode, if nonnegative, ending bunch number for computations 

ACAUSAL_ALLOWED  long  0  If nonzero, then an acausal wake is allowed. 

GROUP  string  NULL  Optionally used to assign an element to a group, with a userdefined 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 equispaced, 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 att = 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 autoscaling 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:
Bunchedmode application of the shortrange wake is possible using speciallyprepared 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.
WATCH