Numerical Simulation for the Riga Dynamo

The critical magnetic Reynolds number (Rm) of the Riga dynamo experiment depends
strongly on the shape of its velocity profiles. For given motor power ressources it is
necessary to optimize these profiles in order to achieve self-excitation of the magnetic
field. We present a number of one- and two-dimensional calculations for a variety of
axial and azimuthal velocities. Particularly, we test velocity profiles with maximal
helicity (Bessel function profile). For these velocity profiles the critical Rm can
be reduced by 20 per cent compared to the value for the solid body rotation profile.
The used two-dimensional finite difference solver allows to study the effect of
axially varying profiles, too. In addition, we present some two-dimensional
calculations for further dynamo experiments in cylindrical geometry, including
the flow topologies s1t1, s2t1 and s2t2. The influence of the flow direction and
the effect of a surrounding conducting medium on the critical Rm is investigated
in detail.