r0beam 0.01[m] "Initial beam radius"
r0 0.05[m] "Domain radius"
L 0.2[m] "Domain length"
Ibeam 3[A] "Beam current magnitude"
v0beam 1e8[m/s] "Initial beam velocity"
gamma 1/sqrt(1-(v0beam/c_const)^2) "Relativistic factor"
K e_const*Ibeam/(2*pi*epsilon0_const*me_const*(v0beam*gamma)^3) "Generalized perveance"
hmax 0.01 "Maximum mesh element size"