Sheared helical turbulence and the helicity constraint in large-scale   dynamos
  The effect of shear on the growth of large scale magnetic fields in helical turbulence is investigated. The resulting large-scale magnetic field is also helical and continues to evolve, after saturation of the small scale field, on a slow resistive time scale. This is a consequence of magnetic helicity conservation. Because of shear, the time scale needed to reach an equipartition-strength large scale field is shortened proportionally to the ratio of the resulting toroidal to poloidal large scale fields. 
A. Bigazzi (1), A. Brandenburg (2 and 3), K. Subramanian (4) ((1)   Department of Mathematics, Politecnico di Milano, Italy,...