  The mathematics and physics of each of the three aspects of magnetic field
evolution -- topology, energy, and helicity -- is remarkably simple and clear.
When the resistivity $\eta$ is small compared to an imposed evolution, $a/v$,
timescale, which means $R_m\equiv\mu_0va/\eta>>1$, magnetic field line chaos
dominates the evolution of field-line topology in three-dimensional systems.
Chaos has no direct role in the dissipation of energy. A large current density,
$j_\eta\equiv vB/\eta$, is required for energy dissipation to be on a
comparable time scale to the topological evolution. Nevertheless, chaos plus
Alfv\'en wave damping explain why both timescales tend to be approximately an
order of magnitude longer than the evolution timescale $a/v$. Magnetic helicity
is injected onto tubes of field lines when boundary flows have vorticity. Chaos
can spread but not destroy magnetic helicity. Resistivity has a negligible
effect on helicity accumulation when $R_m>>1$. Helicity accumulates within a
tube of field lines until the tube erupts and moves far from its original
location.
