Specify the temporal evolution of the radius of the cavity, if it exists
Author: Frederic Masset
CavityWidthor a temperature transition defined by
TransitionWidth. It is used to vary the cavity or temperature transition radius with time (this parameter was first introduced to show that a planet locked at a cavity edge is trapped by this latter, since it follows its radial evolution). More precisely, this parameter must be set to the inverse of the timescale over which the cavity radius is doubled with respect to its value at run start (or restart). The cavity radius is an affine function of time.
LambdaDoublingdefaults to 0, which yields a constant cavity or transition radius.