Speaker
Dr
Matthias Reinhard
Description
Examples with purely magnetic as well as MHD backgrounds are
studied where the quasi-kinematic test-field method breaks
down. In cases with homogeneous mean fields it is shown that
the generalized method produces the same results as the
imposed-field method, where the field-aligned component of
the actual electromotive force from the simulation is used.
For MHD backgrounds, new mean-field effects are found that
depend on cross-correlations between magnetic and velocity
fluctuations. In particular, there is a contribution to the
mean Lorentz force that is linear in the mean field and
hence reverses sign upon a reversal of the mean field. For
strong mean fields, α is found to be quenched proportional
to the fourth power of the field strength, regardless of the
type of background studied. An analogous method for
compressible isothermal hydrodynamics is presented which
reliably reproduces SOCA results. In particular, the AKA
effect and negative turbulent viscosity for the Roberts flow
is demonstrated.
