  Drilling holes in a bulk high-Tc superconductor enhances the oxygen annealing
and the heat exchange with the cooling liquid. However, drilling holes also
reduces the amount of magnetic flux that can be trapped in the sample. In this
paper, we use the Bean model to study the magnetization and the current line
distribution in drilled samples, as a function of the hole positions. A single
hole perturbs the critical current flow over an extended region that is bounded
by a discontinuity line, where the direction of the current density changes
abruptly. We demonstrate that the trapped magnetic flux is maximized if the
center of each hole is positioned on one of the discontinuity lines produced by
the neighbouring holes. For a cylindrical sample, we construct a polar
triangular hole pattern that exploits this principle; in such a lattice, the
trapped field is ~20% higher than in a squared lattice, for which the holes do
not lie on discontinuity lines. This result indicates that one can
simultaneously enhance the oxygen annealing, the heat transfer, and maximize
the trapped field.
