  We study chiral magnetic effect in collisions of AuAu, RuRu and ZrZr at s =
200GeV. The axial charge evolution is modeled with stochastic hydrodynamics and
geometrical quantities are calculated with Monte Carlo Glauber model. By
adjusting the relaxation time of magnetic field, we find our results in good
agreement with background subtracted data for AuAu collisions at the same
energy. We also make prediction for RuRu and ZrZr collisions. We find a weak
centrality dependence of initial chiral imbalance, which implies the centrality
dependence of chiral magnetic effect signal comes mainly from those of magnetic
field and volume factor. Our results also show an unexpected dependence on
system size: while the system of AuAu has larger chiral imbalance and magnetic
field, it turns out to have smaller signal for chiral magnetic effect due to
the larger volume suppression factor.
