Turbulent dynamos and magnetic helicity

It is shown that the turbulent-dynamo alpha effect converts magnetic helici ty from the turbulent field to the mean field when the turbulence is electr omagnetic, while the magnetic helicity of the mean field is transported acr oss space when the turbulence is electrostatic or due to the electron diama gnetic effect. In all cases, however, the dynamo effect strictly conserves the total helicity except for resistive effects and a small battery effect. Implications for astrophysical situations, especially for the solar dynamo , are discussed.