  We have measured the depinning of trapped kinks in a ratchet potential using
a fabricated circular array of Josephson junctions. Our ratchet system consists
of a parallel array of junctions with alternating cell inductances and
junctions areas. We have compared this ratchet array with other circular
arrays. We find experimentally and numerically that the depinning current
depends on the direction of the applied current in our ratchet ring. We also
find other properties of the depinning current versus applied field, such as a
long period and a lack of reflection symmetry, which we can explain
analytically.
