res_diff_time Function

  function res_diff_time()
    !! author: J. Morris (UKAEA)
    !!
    !! Calculates resistive diffusion time

    ! Module variables
    use physics_variables, only : rmajor, rplas, kappa95
    use constants, only : rmu0

    ! Return value
    real(dp) :: res_diff_time

    res_diff_time = 2.0D0*rmu0*rmajor / (rplas*kappa95)
    !! Resistive diffusion time equals the current penetration time which is approximated by:
    !! \begin{equation} t_{\text{res-diff}} \sim
    !! \frac{2\mu_0.R_0}{\rho_{\text{plasma}}\kappa_{95}}\end{equation}
    !!
    !! * \( \mu_0 \) -- permittivity of free space [H/m]
    !! * \( R_0 \) -- plasma major radius [m]
    !! - \( \rho_{\text{plasma}} \) -- plasma resistivity [Ohms]
    !! - \( \kappa_{95} \) -- plasma elongation at 95% flux surface
    !!
    !! #TODO Reference needed

  end function res_diff_time