  Roebel cables and superconducting tape coils are often modeled as stacks of
parallel superconducting tapes carrying the same transport current. We solved,
in the infinitely thin approximation, the transport current and magnetization
problems for such stacks using an efficient numerical scheme based on a
variational formulation of the Kim critical-state model. We also refined the
anisotropic bulk approximation, introduced by Clem et al. in order to simplify
AC loss estimates for densely packed stacks of many tapes; this was achieved by
removing the simplifying assumptions on the current sheet density in the
subcritical zone and the shape of this zone boundary. Finally, we studied
convergence of stack problem solutions to the solution of the modified bulk
problem. It was shown that, due to the fast convergence to the anisotropic bulk
limit, accurate AC loss estimates for stacks of hundreds of tapes can usually
be obtained also using a properly rescaled model of a stack containing only
ten-twenty tapes.
