An example of a Variable Frequency RF cavity of cyclotron with

polynomial time dependence of parameters is given below:

===== Spline Time Dependence

The `SPLINE_TIME_DEPENDENCE` element is used to define time

dependent parameters in RF cavities in terms of a first or third order

spline fit.

ORDER::

Order of the lookup - either 1 for linear interpolation, or 3 for cubic

interpolation with quadratic smoothing. Other values make an error.

TIMES::

Array of real times in ns. There must be at least `ORDER`+1 elements in the

array and they must be strictly monotically increasing.

VALUES::

Array of real values. The length of `VALUES` must be the same as the length

of `TIMES`.

[[sec.elements.variable-rf-cavity-fringe-field]]

==== Fringe Field

It is possible to model a soft-edged RF cavity with time dependent parameters using the `VARIABLE_RF_CAVITY_FRINGE_FIELD` element. This will place a full cavity including the field body and fringe fields. `VARIABLE_RF_CAVITY_FRINGE_FIELD` must be placed using the `RingDefinition` element.