Effect of anomalous transport on plasma convection in the poloidal limiter shadow of a tokamak

Abstract

Steady state plasma flow in the poloidal limiter shadow of a tokamak is analysed. The authors assume anomalous diffusion and thermal conductivity and find the radial and poloidal dependence of electric potential, plasma density and electron temperature. Top-bottom asymmetry of the plasma parameters is demonstrated. The presence of a strong electric field leads to plasma convection.

Characterization of tokamak edge turbulence by far-infrared laser scattering and Langmuir probes

“…None of these models includes poloidal and toroidal asymmetries. The theoretical model of Nedospasov et al [23,24] can predict asymmetries, but the diffusion coefficient is more than an order of magnitude smaller than the measured one.…”

“…Measurements carried out on the TV-1 tokamak also indicate the existence of poloidal asymmetries in the shadow of the limiter [23]. A possible explanation for these asymmetries is the existence of a poloidal electric field caused by the asymmetric potential jump on the ion and electron drift side of the limiter [23,24].…”

Plasma boundary phenomena in tokamaks

“…The limiter sink is not always the dominant one for the SOL, and in Section 3.6 the 'complex SOL' is considered for cases where other sinks, such as radiation, and localized sources (ionization) are important. Two-dimensional plasma code modelling [147] and neoclassical [7,[148][149][150][151][152] SOL theory are not discussed.…”

“…Since v. e > 1, one might anticipate that SOLs would be in the neoclassical Pfirsch-Schliiter (P-S, collisional) [479] regime and that the P-S drifts resulting from toroidal geometry would be important in the SOL. Some modelling of the SOL has been carried out on this basis [7,[148][149][150][151][152], but it generally leads to underestimates of the measured cross-field transport rates and of the SOL thickness X s , i.e., transport is anomalous. Thus, the more usual procedure is to ignore toroidal and neoclassical effects altogether in the SOL and to invoke anomalous cross-field transport rates for particles and heat, which are adjusted to give agreement with the measured SOL widths for particle and energy density (see Section 3.4).…”

EDGE2D code simulations of SOL flows and in–out divertor asymmetries in JET

“…One such mechanism leading to the convective flux in the SOL can be a radial drift in the poloidal electric field E h [5,24,25]. However, the 2D fluid code calculates a value of E h that would be too low by a factor of $10 to generate the proposed radial flux velocity of 10 m/s.…”