def plasma_freq(n_e):
    """
    Given an electron density parameter (n_e), compute the plasma frequency.
    """
    eps0 = 8.8542E-12           #[A*s/(V*m)]    Permittivity
    e    = 1.602E-19            #[C]            Elementary charge
    me   = 9.109E-31            #[kg]           Electron rest mass
    omega_p  = ((e**2)*n_e/(eps0*me))**0.5  #[Hz]   Plasma frequency
    return omega_p