Parallel 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 | double | 0.0 | beam charge (or use CHARGE element) | |

FACTOR | double | 1 | factor to multiply wake by | |

N_BINS | long | 128 | number of bins for current histogram | |

INTERPOLATE | long | `0` |
interpolate wake? | |

SMOOTHING | long | `0` |
Use Savitzky-Golay filter to smooth current histogram? | |

SG_HALFWIDTH | long | 4 | Savitzky-Golay filter half-width for smoothing | |

SG_ORDER | long | 1 | Savitzky-Golay 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 non-zero, then do calculations bunch-by-bunch. | |

GROUP | string | NULL | 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,
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. A
positive value of time represents the distance behind the exciting
particle.

A positive value of results in energy *loss*. A physical
wake function should be positive at .

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:

- Compute the arrival time of each particle at the wake element. This
is necessary because
`elegant`uses the longitudinal coordinate . - Find the mean, minimum, and maximum arrival times (, , and
, respectively). If
is greater than the duration of
the wakefield data, then
`elegant`either exits (default) or issues a warning (if`ALLOW_LONG_BEAM`

is nonzero). In the latter case, that part of the beam that is furthest from is ignored for computation of the wake. - If the user has specified a fixed number of bins (not recommended), then
`elegant`centers those bins on . Otherwise, the binning range encompasses to , where is the spacing of data in the wake file. - Create the arrival time histogram. If any particles are outside the histogram range, issue a warning.
- If
`SMOOTHING`

is nonzero, smooth the arrival time histogram. - Convolve the arrival time histogram with the wake function.
- Multiply the resultant wake by the charge and any user-defined factor.
- Apply the energy changes for each particle. This is done in such a way that the transverse momentum are conserved.
- If
`CHANGE_P0`

is nonzero, change the reference momentum of the beamline to match the average momentum of the beam.

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.