Add twiss injection source

[bnara]

Add twiss injection source. Our need for this was to inject a beam with independent control of phase-space in all three Cartesian directions, in order to match an asymmetric beam into a plasma ramp. This gives a flexible Twiss parameterization, including transverse focusing and longitudinal compression and chirp. Furthermore, arbitrary orientation and location of beams is supported. Online documentation parameters.rst updated.

Implementation details: twiss-implementation.pdf

phase-space.mp4

Three independent focal distances:

Arbitrary positioning and orientation of beams, including rotation about longitudinal axes:

[bnara]

Illustration of different cutting methods available in twiss

During beam initialization, either "planar" or "ellipsoidal" cuts can be made in 6D phase-space. The user provides six parameters, corresponding to the three Cartesian coordinates and momenta. The parameters are given in units of their respective focal rms standard deviations. Specifying the numerical constant inf effectively disables cutting along the corresponding axis. An ellipsoidal cut and a planar cut can be simultaneously used.

The gaussian_beam source provides planar cuts along 3 coordinate directions. To make the same cut in twiss, use:

beam.twiss.planar_cut = 1 1 1 inf inf inf

planar-cut.mp4

To make an ellipsoidal cut in all six coordinate and momenta at one standard deviation, use:

beam.twiss.ellipsoidal_cut = 1 1 1 1 1 1

ellipsoidal-cut.mp4