Transverse 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 functions 

TCOLUMN  STRING  NULL  column in INPUTFILE containing time data 

WXCOLUMN  STRING  NULL  column in INPUTFILE containing x Green function 

WYCOLUMN  STRING  NULL  column in INPUTFILE containing y Green function 

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

XFACTOR  double  1  factor by which to multiply x wake 

YFACTOR  double  1  factor by which to multiply y 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 

DX  M  double  0.0  misalignment 
DY  M  double  0.0  misalignment 
TILT  RAD  double  0.0  rotation about longitudinal axis 
X_DRIVE_EXPONENT  long  1  Exponent applied to x coordinates of drive particles 

Y_DRIVE_EXPONENT  long  1  Exponent applied to y coordinates of drive particles 

X_PROBE_EXPONENT  long  0  Exponent applied to x coordinates of probe particles 

Y_PROBE_EXPONENT  long  0  Exponent applied to y coordinates of probe particles 

TRWAKE continued
Transverse wake specified as a function of time lag behind the particle.
Parameter Name  Units  Type  Default  Description 
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 transversewake Green functions, W_{x}(t) and W_{y}(t), versus time behind the particle. The units of the wakes are V/C/m, 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. Time values must be equally spaced.
The sign convention for W_{q} (q being x or y) is as follows: a particle with q > 0 will impart a positive kick (Δq^{′} > 0) to a trailing particle following t seconds behind if W_{q}(t) > 0. A physical wake function should be zero at t = 0 and also be initially positive as t increases from 0. Causality requires that W_{q}(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 TRWAKE 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 XFACTOR and YFACTOR parameters can be used to adjust the strength of the wakes if the location at which you place the TRWAKE element has different beta functions than the location at which the object that causes the wake actually resides.
The X_DRIVE_EXPONENT and Y_DRIVE_EXPONENT parameters can be used to change the dependence of the wake on the x and y coordinates, respectively, of the particles. Normally, these have the value 1, which corresponds to an ordinary dipole wake in a symmetric chamber.
If you have an asymmetric chamber, then you will have a transverse wake kick even if the beam is centered. (Of course, you’ll need a 3D wake code like GdfidL or MAFIA to compute this wake.) This part of the transverse wake is modeled by setting X_DRIVE_EXPONENT=0 and Y_DRIVE_EXPONENT=0. It will result in an orbit distortion, but conceivably could have other effects, such as emittance dilution. In this case, the units for the x and y wake must be V∕C. A negative value of the wake corresponds to a kick toward negative x (or y).
In addition, a quadrupole wake can be modeled by setting X_DRIVE_EXPONENT=0, Y_DRIVE_EXPONENT=0, X_PROBE_EXPONENT=1, and Y_PROBE_EXPONENT=1. The kick to a particle now depends on it’s displacement, not on the displacement of the leading particles. In this case, the units for the wakes must be V∕C∕m.
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 TRWAKE element is controlled using the BUNCHED_BEAM_MODE parameter
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