  We perform nonlinear MHD simulations to study the propagation of
magnetoacoustic waves from the photosphere to the low corona. We focus on a 2D
system with a gravitationally stratified atmosphere and three photospheric
concentrations of magnetic flux that give rise to a magnetic null point with a
magnetic dome topology. We find that a single wavepacket introduced at the
lower boundary splits into multiple secondary wavepackets. A portion of the
packet refracts towards the null due to the varying Alfv\'en speed. Waves
incident on the equipartition contour surrounding the null, where the sound and
Alfv\'en speeds coincide, partially transmit, reflect, and mode convert between
branches of the local dispersion relation. Approximately $15.5\%$ of the
wavepacket's initial energy ($E_{input}$) converges on the null, mostly as a
fast magnetoacoustic wave. Conversion is very efficient: $70\%$ of the energy
incident on the null is converted to slow modes propagating away from the null,
$7\%$ leaves as a fast wave, and the remaining $23\%$ (0.036$E_{input}$) is
locally dissipated. The acoustic energy leaving the null is strongly
concentrated along field lines near each of the null's four separatrices. The
portion of the wavepacket that refracts towards the null, and the amount of
current accumulation, depends on the vertical and horizontal wavenumbers and
the centroid position of the wavepacket as it crosses the photosphere. Regions
that refract towards or away from the null do not simply coincide with regions
of open versus closed magnetic field or the local field orientation. We also
modeled wavepacket propagation using a WKB method and found that it agrees
qualitatively, though not quantitatively, with the results of the numerical
simulation.
