  We experimentally realize a sophisticated structure geometry for reliable
magnetic domain wall-based multi-turn-counting sensor devices, which we term
closed-loop devices that can sense millions of turns. The concept relies on the
reliable propagation of domain walls through a cross-shaped intersection of
magnetic conduits, to allow the intertwining of loops of the sensor device. As
a key step to reach the necessary reliability of the operation, we develop a
combination of tilted wires called the syphon structure at the entrances of the
cross. We measure the control and reliability of the domain wall propagation
individually for cross-shaped intersections, the syphon geometries and finally
combinations of the two for various field configurations (strengths and
angles). The various measured syphon geometries yield a dependence of the
domain wall propagation on the shape that we explain by the effectively acting
transverse and longitudinal external applied magnetic fields. The combination
of both elements yields a behaviour that cannot be explained by a simple
superposition of the individual different maximum field operation values. We
identify as an additional process the nucleation of domain walls in the cross,
which then allows us to fully gauge the operational parameters. Finally, we
demonstrate that by tuning the central dimensions of the cross and choosing the
optimum angle for the syphon structure reliable sensor operation is achieved,
which paves the way for disruptive multi-turn sensor devices.
