Screw dynamo in a time-dependent pipe flow.
The kinematic dynamo problem is investigated for the flow of a conducting fluid in a cylindrical, periodic tube with conducting walls. The methods used are an eigenvalue analysis of the steady regime, and the three-dimensional solution of the time-dependent induction equation. The configuration and parameters considered here are close to those of a dynamo experiment planned in Perm, which will use a torus-shaped channel. We find growth of an initial magnetic field by more than three orders of magnitude. A marked field growth can be obtained if the braking time is less than 0.2 s and only one diverter is used in the channel. The structure of the seed field has a strong impact on the field amplification factor. Generation properties can be improved by adding ferromagnetic particles to the fluid in order to increase its relative permeability, but this will not be necessary for the success of the dynamo experiment. For higher magnetic Reynolds numbers, the nontrivial evolution of different magnetic modes limits the value of simple "optimistic" and "pessimistic" estimates.
Dobler
Wolfgang
W
Kiepenheuer-Institut für Sonnenphysik, Schöneckstrasse 6, D-79104 Freiburg, Germany. Wolfgang.Dobler@kis.uni-freiburg.de
Frick
Peter
P
Stepanov
Rodion
R