Stochastic magnetic fields in a weakly collisional plasma enhance the colli
sionality of electrons in the medium compared to the classical Spitzer valu
es. The reduction in the thermal conductivity may play an important role in
the evolution of galaxy clusters. This work extends prior work by examinin
g the parallel propagation of electrons in plasma media where the magnetic
field amplitude sampled along a field line is a stochastic function of the
distance. New physics is exhibited when many large-amplitude magnetic mirro
rs are present; the parallel transport becomes subdiffusive rather than dif
fusive in this limit. The transition between diffusion and subdiffusion can
be obtained from properties of the asymptotic solution to the kinetic equa
tion in the vicinity of a solitary magnetic mirror. This transition has bee
n computed as a function of the power law exponent in the distribution of m
irror maxima, and the asymptotic scaling of the mean-squared electron displ
acement with time has been obtained in these systems as a function of this
exponent. Monte Carlo comparisons are in agreement with these results. (C)
2001 American Institute of Physics.