  We resolve the inner region of a massive cluster forming in a cosmological
LCDM simulation with a mass resolution of 2*10^6 Msun and before z=4.4 even
3*10^5 Msun. This is a billion times less than the clusters final virial mass
and a substantial increase over current LCDM simulations. We achieve this
resolution using a new multi-mass refinement procedure and are now able to
probe a dark matter halo density profile down to 0.1 percent of the virial
radius. The inner density profile of this cluster halo is well fitted by a
power-law rho ~ r^-gamma down to the smallest resolved scale. An inner region
with roughly constant logarithmic slope is now resolved, which suggests that
cuspy profiles describe the inner profile better than recently proposed
profiles with a core. The cluster studied here is one out of a sample of six
high resolution cluster simulations of Diemand et al. (2004) and it's inner
slope of gamma = 1.2 lies close to the sample average.
