  We have studied the magnetic-field dependence of both dark-count rates and
photon-count rates in a superconducting nanowire single-photon detector made of
TaN in external magnetic fields $|\mu_0H| < 10$ mT perpendicular to the plane
of the underlying meander structure and at $T = 4$ K. The dark-count rates show
a characteristic field-dependence, which is asymmetric with respect to magnetic
field direction. The field- and the current dependence of the dark counts can
be quantitatively well explained if one assumes that the critical current is
reduced to $\approx50%$ at the $180^\circ$ meander turns when compared to a
straight strip, and the observed asymmetry can be modeled assuming that the
turnarounds are not all strictly equal. Surprisingly, the photon count rates do
not show any significant field dependence, which seems to be at odds with
existing detection models invoking vortex crossings.
