Anomalous and neoclassical transport suppression by the radial electric field, induced by Alfvén waves in tokamaks

Abstract

The suppression of anomalous transport and/or reduction of neoclassical transport caused by the Alfvén-wave-induced shear of the radial electric field in tokamaks is investigated. The simple quantitative estimates reported in previous papers are checked by a consistent evaluation of the profile of the radial electric field created by the resonant absorption of Alfvén waves. The radial variations of the ion viscosity and heat conductivity across the mode conversion layer are evaluated both in the banana and potato regions. In agreement with previous analytical results, it is shown that the kinetic Alfvén waves may play the role of a convenient mechanism for reduction of anomalous and neoclassical transport and formation of transport barriers in tokamaks.

The combined toroidicity, ellipticity and triangularity effects on the energy deposition of Alfvén modes in pre-heated, low aspect ratio tokamaks

“…, from the ion momentum equation, the following simple approximate expression for E r is found [39]:…”

Role of trapped and circulating particles in inducing current drive and radial electric field by Alfvén waves in tokamaks

“…It was previously shown that radiofrequency (RF) forces, affecting electrons, F h e , and ions, F h i , respectively, in closed magnetic traps, can be presented in the following form (Tsypin et al 1999) (here we are interested only in poloidal (s = θ) and toroidal (s = ζ) components of RF forces):…”

“…Recently, new ideas for the application of AWs in tokamaks, besides heating and current drive, have been investigated with great interest. They are all related to the electric field created by these waves at the mode resonant surface, and the associated sheared plasma rotation (Craddock and Diamond 1991;Tsypin et al 1999), with the purpose of maintaining internal transport barriers in tokamaks (Biglari et al 1990;Burrell 1997;Tsypin et al 1998Tsypin et al , 1999. In particular, a new research program has been initiated in the TCABR tokamak (Tokamak Chauffage Alfvén Brazilian) to investigate this mechanism (Galvão et al 1999).…”

Plasma-turbulence suppression and transport-barrier formation by externally driven radiofrequency waves in spherical tokamaks

“…According to transport-barrier theory, in order to be effective, this flow shear must be greater than the most dangerous plasma instability increment (see e.g. Burrell 1997;Sesnic et al 1998;Tsypin et al 1999).…”

“…Under certain simplifying assumptions, including the condition c s > U iθ > {h θ U iφ , U ip } (where U iθ and U iφ are the ion poloidal and toroidal fluid velocities; U ip is the pressure-gradient-generated ion velocity; h θ ≡ B θ /B; and c s = [(T e + T i )/n i ] 1/2 is the ion sound speed, where n i is the ion number density, and T i and T e are the ion and electron temperatures), the following simple approximate expression for E r is found from the ion momentum equation (Tsypin et al 1999):…”