Suppressed fluctuations..

Abstract

Suppression of fluctuations of normally perturbed magnetic fields in dynamo waves and slow dynamos along curved (folded), torsioned (twisted) and non-stretched, diffusive filaments are obtained. This form of fluctuations suppression has been recently obtained by Vainshtein et al [PRE 56, (1997)] in nonlinear ABC and stretch-twist-fold (STF) dynamos by using a magnetic Reynolds number of the order of $Rm\approx{10^{4}}$. Here when torsion does not vanish an expression between magnetic Reynolds number and length scale L as with constant torsion ${\tau}_{0}$ itself is obtained, such as $Rm\approx{\frac{{\tau}_{0}L}{\eta}}$ is obtained. At coronal loops $Rm\approx{10^{12}}$ and torsion of the twisted structured loop from astronomical data by Lopez-Fuentes et al [Astron. and Astrophys. (2003)] of ${\tau}\approx{9.0{\times}10^{-10}}cm^{-1}$ is used to compute a very slow magnetic diffusion of ${\eta}\approx{10^{-8}}$. The slow dynamo obtained here is in agreement with Vishik arguement that fast dynamo cannot be obtained in non-stretched dynamo flows. When torsion vanishes helical turbulence is quenched and but ${\alpha}$-dynamos cannot be maintained since exponential stretching depends on torsion. This is actually Zeldovich antidynamo theorem for torsion-free or planar filaments which has been discussed by the other also recently in another context [Astr Nach. (2008)]. The suppression of magnetic field fluctuations is actually a result of the coupling of the magnetic diffusion and Frenet torsion of helical turbulence.