  Motivated by recent proposals to realize Majorana bound states in chains and
arrays of magnetic atoms deposited on top of a superconductor, we study the
topological properties of various chain structures, ladders and two-dimensional
arrangements exhibiting magnetic helices. We show that magnetic domain walls
where the chirality of a magnetic helix is inverted support two protected
Majorana states giving rise to a tunneling conductance peak twice the height of
a single Majorana state. The topological properties of coupled chains exhibit
nontrivial behaviour as a function of the number of chains beyond the even-odd
dichotomy expected from the simple $\mathbb{Z}_2$ nature of coupled Majorana
states. In addition, it is possible that a ladder of two or more coupled chains
exhibit Majorana edge states even when decoupled chains are trivial. We
formulate a general criterion for the number of Majorana edge states in
multichain ladders and discuss some experimental consequences of our findings.

Mesoscale and Nanoscale Physics;Superconductivity