lApproximation of long beams:
– Beam length is much
longer than beam radius;
–Therefore, beam can be described by a number of weakly
interacting slices.
–The electric field is found from radial Poisson’s equation.
–As a result of the simplification the second code is hundreds
times faster than the first one and can be used for most cases, while the
first code provides benchmarking for the second.