  The adiabatic chiral magnetic effect (CME) is a phenomenon by which a slowly
oscillating magnetic field applied to a conducting medium induces an electric
current in the instantaneous direction of the field. Here we theoretically
investigate the effect in a ballistic Weyl semimetal sample having the geometry
of a slab. We discuss why in a general situation the bulk and the boundary
contributions towards the CME are comparable. We show, however, that under
certain conditions the adiabatic CME is dominated by the Fermi arc states at
the boundary. We find that despite the topologically protected nature of the
Fermi arcs, their contribution to the CME is neither related to any topological
invariant nor can generally be calculated within the bulk low-energy effective
theory framework. For certain types of boundary, however, the Fermi arcs
contribution to the CME can be found from the effective low energy Weyl
Hamiltonian and the scattering phase characterising the collision of a Weyl
excitation with the boundary.
