  We present microwave measurements for the density and spatial correlation of
current critical points in an open billiard system, and compare them with the
predictions of the Random Wave Model (RWM). In particular, due to a novel
improvement of the experimental set-up, we determine experimentally the spatial
correlation of saddle points of the current field. An asymptotic expression for
the vortex-saddle and saddle-saddle correlation functions based on the RWM is
derived, with experiment and theory agreeing well. We also derive an expression
for the density of saddle points in the presence of a straight boundary with
general mixed boundary conditions in the RWM, and compare with experimental
measurements of the vortex and saddle density in the vicinity of a straight
wall satisfying Dirichlet conditions.
