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The generation of a magnetic field by dynamo action in a Taylor-vortex flow is investigated numerically.We first discuss how the Taylor vortices generate a spatially subharmonic dynamo, for which the axial wavelength of the magnetic field is twice the one of the flow pattern. Then, we investigate the influence of the Reynolds number and the turbulent fluctuations on the structure and the onset of the Taylor-Couette dynamo. Finally, based on the subharmonic nature of this dynamo, we propose new configurations which could be relevant for laboratory experiments. [ABSTRACT FROM AUTHOR]

The effect of turbulent fluctuations on the zonal (flux surface averaged) magnetic field in drift-ballooning turbulence is shown to be equivalent to a turbulent anti-resistivity. The flux surface average of the convective nonlinearity in Ohm’s law is proportional to the flux surface average of the current. The coefficient of proportionality can be defined as a turbulent resistivity ηturb. The correlation of the flux surface average of the convective nonlinearity with the negative of the flux surface average of the current is nearly 100%. Because the convective nonlinearity is correlated with the negative of the current, and not the current, the turbulent resistivity is negative. The magnitude of ηturb is virtually identical to the magnitude of the collisional resistivity η, but opposite in sign, so that the total resistivity ηtotal=η+ηturb is nearly zero. The effect of the fluctuations is to balance the effect of collisional resistive diffusion. As a result, while the energy in the zonal flow increases to a large value as the fluctuations grow and saturate, the energy in the zonal magnetic field remains very small. [ABSTRACT FROM AUTHOR]

We study the dynamo threshold of a helical flow made of a mean plus a fluctuating part. Two flow geometries are studied: (i) solid body and (ii) smooth. Two well-known resonant dynamo conditions, elaborated for stationary helical flows in the limit of large magnetic Reynolds numbers, are tested against lower magnetic Reynolds numbers and for fluctuating flows with zero mean. For a flow made of a mean plus a fluctuating part, the dynamo threshold depends on the frequency and the strength of the fluctuation. The resonant dynamo conditions applied on the fluctuating (respectively, mean) part seems to be a good diagnostic to predict the existence of a dynamo threshold when the fluctuation level is high (respectively, low). [ABSTRACT FROM AUTHOR]