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Abstract: Anti-dynamo modes are usually found in spheromaks plasma devices experimentsdue to the fact that Cowling anti-dynamo theorem is naturally applied toaxisymmetric devices and flows. In this paper full consideration is given tothe existence of slow dynamo modes in the case of compact Riemannian plasmadevices without boundaries, such as tokamaks, stellarators and torsatrons. Itis shown that a perturbed untwisted flow given by a decaying mode magneticfield is able to generate a slow twisted dynamo plasma flow where theunperturbed flow is also a steady flow. When the slow dynamo limit is obtainedfor high Reynolds magnetic numbers $Rm$, the unperturbed plasma flow achieveequilibrium as in spheromaks. The data of aspect ratio and other data obtainedfrom the Brazilian spherical tokamak at the National institute for spaceresearch are used to obtain a numerical estimate for the maximum magneticgrowth rate of the magnetic field of the slow dynamo action as${\gamma} {1max}\approx{\frac{0.26}{a}{\times}\frac{v {1{\theta}}}{B {1s}}}$for a toroidal initial magnetic field $B {0}\approx{0.4T}$ and an aspect datatokamak of 1.5. For a tokamak internal radius of $a\approx{0.2m}$ one obtains amaximum growth rate for the slow dynamo as${\gamma} {1max}\approx{1.3{\times}\frac{v {1{\theta}}}{B {1s}}}$, where$v {1{\theta}}$ is the poloidal perturbed diffusive flow. The safety factor isgiven by $q\approx{-1}$ which is $q<1$ implying stability of spherical tokamakplasma.



Author: Garcia de Andrade

Source: https://arxiv.org/







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