  The possible occurrence of dead zones in protoplanetary disks subject to the
magneto-rotational instability highlights the importance of disk ionization. We
present a closed-form theory for the deep-down ionization by X-rays at depths
below the disk surface dominated by far-ultraviolet radiation. Simple analytic
solutions are given for the major ion classes, electrons, atomic ions,
molecular ions and negatively charged grains. In addition to the formation of
molecular ions by X-ray ionization of H2 and their destruction by dissociative
recombination, several key processes that operate in this region are included,
e.g., charge exchange of molecular ions and neutral atoms and destruction of
ions by grains. Over much of the inner disk, the vertical decrease in
ionization with depth into the disk is described by simple power laws, which
can easily be included in more detailed modeling of magnetized disks. The new
ionization theory is used to illustrate the non-ideal MHD effects of Ohmic,
Hall and Ambipolar diffusion for a magnetic model of a T Tauri star disk using
the appropriate Elsasser numbers.
