r0beam 0.01[m] "Initial beam radius" r0 0.05[m] "Domain radius" L 0.2[m] "Domain length" Ibeam 1[uA] "Beam current magnitude" v0beam 1e6[m/s] "Initial beam velocity" gamma 1 "Relativistic factor" K e_const*Ibeam/(2*pi*epsilon0_const*me_const*(v0beam*gamma)^3) "Generalized perveance" hmax 0.005 "Maximum mesh element size"