  We study gravitational wave emission and the structure and formation of
apparent horizons in orbiting black-hole binary systems in higher-dimensional
general relativity. For this purpose we present an apparent horizon finder for
use in higher dimensional numerical simulations and test the finder's accuracy
and consistency in single and binary black-hole spacetimes. The black-hole
binaries we model in $D=6$ dimensions complete up to about one orbit before
merging or scatter off each other without formation of a common horizon. In
agreement with the absence of stable circular geodesic orbits around
higher-dimensional black holes, we do not find binaries completing multiple
orbits without finetuning of the initial data. All binaries radiate about
$0.13\,\%$ to $0.2\,\%$ of the total mass-energy in gravitational waves, over
an order of magnitude below the radiated energy measured for four-dimensional
binaries. The low radiative efficiency is accompanied by relatively slow
dynamics of the binaries as expected from the more rapid falloff of the binding
gravitational force in higher dimensions.
