  We calculate the evaporation of a cool accretion disk around a black hole due
to the ion-bombardment by an ion supported accretion flow (here ISAF, or
optically thin ADAF). As first suggested by Spruit & Deufel (2002), this
evaporation takes place in two stages: ion bombardment of the cool disk
(Shakura-Sunyaev disk: SSD) produces an intermediate-temperature layer on top
of the disk (`warm layer') which constitutes an independent accretion flow on
both sides of the SSD. As this warm material accretes inward of the inner
radius of the SSD, it becomes thermally unstable by lack of cooling of photons,
and evaporates into the ISAF, thereby feeding the latter. Angular momentum
conservation forces a certain fraction of the ISAF material to move outward,
where it can bombard the SSD with its hot ions. The flow geometry is derived by
computing stationary solutions of the continuity- and angular momentum
equations for the three components (ISAF, warm flow and SSD). The overall
radiative output is dominated by hard X-rays. They are produced mostly from the
warm component, rather than the ISAF. The expected time dependence and
stability of the flow, not computed here, is discussed briefly.
