Calculations of wave excitation and dissipation in Tokamak Chauffage Alfvén wave heating experiment in Brazil

Abstract

The results of numerical calculations of Alfvén wave absorption are discussed for the experimental conditions foreseen for the Tokamak Chauffage Alfvén wave heating experiment in Brazil (TCABR) [Nucl. Fusion 30, 503 (1996)]. In particular, the effect of toroidal mode coupling on the power deposition of Global Alfvén Wave (GAW) eigenmodes is carefully investigated. Resonant absorption of the toroidally coupled sidebands causes a broad power deposition close to the plasma boundary which can surpass the power deposition of the main GAW at the plasma center. However, the wave absorption can be somewhat optimized by a proper choice of mode spectrum. The excitation of a pure mode spectrum centered at the toroidal mode numbers n=−4 and −6 leads to better plasma coupling than a spectrum centered at n=−2. Finally, it is shown that a small population of light impurities in a hydrogen plasma can strongly modify the dispersion of the GAW and the toroidal Alfvén continuum.

Low frequency heating and flow driven by the dynamic ergodic divertor in tokamaks

“…A similar antenna model with ∇ · J = 0 has been used for analyses of Alfvén wave dissipation in tokamaks (see, e.g. [13,14]). The toroidal code uses 356 × 79 radial × poloidal mesh points (311×79 in plasma) to describe the coupling over the poloidal mode number m produced by plasma toroidicity; such toroidicity introducing m-values in the plasma lie outside the original antenna spectrum.…”

“…However, to incorporate a gradient contribution to the ponderomotive force, the cylindrical code [13,14] includes an additional finite ion Larmor radius effect in the perpendicular components and a general kinetic description in the parallel component with the most important terms shown below (here, the subscripts (r, b, ||) are introduced to distinguish directions…”

“…To calculate LF field excitation in the discussed plasmas we use the cylindrical and toroidal codes mentioned in the introduction [14,15]. The conditions for their validity, away from the rational surfaces where k || = 0, are satisfied in a peripheral (cold plasma) region extending over approximately the outer third of the minor radius, in a frequency band that is determined by inequalities…”

“…In the first step of the numerical analyses, we apply the cylindrical code [14] for one toroidal and one poloidal wavenumber with high resolution (700 radial mesh points), i.e. 12 points are distributed in r dis in TEXTOR.…”

“…To analyse LF field dissipation we use cylindrical kinetic [13,14] ('cylindrical' hereafter) and two-fluid toroidal [15] ('toroidal' hereafter) codes developed for the calculation of Alfvén wave excitation and dissipation in tokamaks. Besides retention of parallel electron-kinetic and finite ion Larmor radius contributions in the cylindrical code (enabling full evaluation of the ponderomotive forces driving plasma flow), and the toroidal geometry of the toroidal one, the plasma description used in both codes has been rendered identical (strongly collisional).…”