calc_jext Subroutine

  subroutine calc_jext (gnostics, j_ext)
    use mp, only: proc0
    use antenna, only: antenna_apar
    use volume_averages, only: average_theta
    use theta_grid, only: ntgrid
    use kt_grids, only: kperp2, ntheta0, naky
    use diagnostics_config, only: diagnostics_type
    implicit none
    !Passed
    type(diagnostics_type), intent(in) :: gnostics
    integer:: istep
    real, dimension(:,:), intent(out) ::  j_ext
    complex, dimension(:,:,:), allocatable :: j_extz
    !Local 
    integer :: i

    istep = gnostics%istep

    !call get_jext(j_ext)    
    allocate (j_extz(-ntgrid:ntgrid, ntheta0, naky)) ; j_extz = 0.
    call antenna_apar (kperp2, j_extz)       
    j_extz(ntgrid-1,:,:) = 0.
    call average_theta(real(j_extz), j_ext, gnostics%distributed)
    deallocate (j_extz)

    !Do averages with a history variable
    if (proc0) then
       !Save variable to history
       if (gnostics%navg > 1) then
          ! This looks a little odd as we ignore the first step
          if (istep > 1) j_ext_hist(:,:,mod(istep,gnostics%navg)) = j_ext(:,:)
          
          !Use average of history
          if (istep >= gnostics%navg) then
             j_ext=0.
             do i=0,gnostics%navg-1
                j_ext(:,:) = j_ext(:,:) + j_ext_hist(:,:,i) / real(gnostics%navg)
             end do
          end if
       end if
    end if
  end subroutine calc_jext