Non-Twist Field Line Mappings for Tokamaks with Reversed Magnetic Shear
نویسندگان
چکیده
The structure of magnetic field lines in a tokamak with reversed magnetic shear is investigated by means of analytically derived area-preserving non-twist Poincaré maps. The basic configuration is the magnetic field produced by an ergodic limiter, superimposed to the tokamak equilibrium field in suitable coordinates. We consider the cases of one and two resonant modes, focusing on magnetic island dimerization and the formation of a transport barrier in the chaotic layer of field lines.
منابع مشابه
Theory of Enhanced Reversed Shear Mode in Tokamaks
It is shown that toroidal magnetic field ripple induced particle flux can drive poloidal E ×B speed to bifurcate over the local maximum of the nonlinear poloidal (or parallel) viscosity. Here, E is the electric field and B is the magnetic field. This mechansim, together with the turbulence suppression due to the radial gradient of the E ×B and diamagnetic angular velocity, is employed to explai...
متن کاملMagnetic Field Lines, Hamiltonian Dynamics, and Nontwist Systems
Magnetic field lines typically do not behave as described in the symmetrical situations treated in conventional physics textbooks. Instead, they behave in a chaotic manner; in fact, magnetic field lines are trajectories of Hamiltonian systems. Consequently the quest for fusion energy has interwoven, for 50 years, the study of magnetic field configurations and Hamiltonian systems theory. The man...
متن کاملThe Radial Electric Field in a Tokamak with Reversed Magnetic Shear
Neoclassical theory with the impurity rotational velocity is used to evaluate the radial electric field, Er, in tokamaks. The result of using the complete matrix method for the deuterium-carbon plasma is compared with a reduced analytic formula for determining Er [Ernst et al., (1998)]. The analytic formula is shown to overestimate the Er magnitude and its gradient. Two transport measures of th...
متن کاملTheoretical Interpretation of Alfv en Cascades in Tokamaks with Non-monotonic q-pro les
Alfv en spectra in a reversed-shear tokamak plasma with a population of energetic ions exhibit a quasiperiodic pattern of primarily upward frequency sweeping (Alfv en Cascade). Presented here is an explanation for such asymmetric sweeping behavior which involves nding a new energetic particle mode localized around the point of zero magnetic shear.
متن کاملGeneralization of cylindrical spheromak solution to finite beta and large reversed shear
The well-known analytic solution for a spheromak in a cylindrical flux conserver is generalized to the situation of finite b with the shape of the flux conserver now being a dependent quantity. Analytic expressions are found for the poloidal flux surfaces, beta, the safety factors at both the magnetic axis and the wall, and the wall profile. A large reversed shear ~i.e., ratio of safety factor ...
متن کامل