Effects of the parallel acceleration on heavy impurity transport in turbulent tokamak plasmas

Abstract

A process specific to the dynamics of the heavy impurities in turbulent tokamak plasmas is found and analyzed. We show that the parallel stochastic acceleration is strongly coupled to the perpendicular transport and generates a radial pinch velocity. The interaction is produced with the hidden drifts, a quasi-coherent component of the motion that consists of a pair of average radial velocities in opposite directions. The parallel acceleration breaks this symmetry and yields a radial average velocity that can be in the inward or outward direction. The pinch is generated in three-dimensional turbulence, in the presence of a poloidal average velocity. It is significant only for heavy, high Z ions. The transport of the tungsten ions is analyzed in the frame of the minimal test particle model that yields this pinch mechanism. We use a semi-analytical method and numerical simulations. The scaling laws of the pinch velocity and of the diffusion coefficient are found and analyzed in order to drive a clear physical image of these non-linear effects. We conclude that the pinch produced by the non-linear interaction of the parallel accelerated motion with the perpendicular transport is rather strong for the heavy impurities.

Effects of intermittency via non-Gaussianity on turbulent transport in magnetized plasmas

“…The transport coefficients, diffusion and average velocity, are computed as simple statistical averages over the ensemble. DNS tries to mimic the whole (real) statistical problem resorting to numerical tools (Palade 2021;Vlad et al 2021).…”

“…The rest of the method remains unchanged. For more details see , Hauff & Jenko (2006), , Vlad et al (2021) and Palade (2021).…”

Scaling laws of two-dimensional incompressible turbulent transport

“…Regarding the specific numerical approach on computing the diffusion coefficients, we employ here the so-called direct numerical simulation method (DNS) [13,36,37]. DNS attempts to mimic the real trajectories {x(t)} at the numerical level.…”

Effects of intermittency on turbulent transport in magnetized plasmas

“…The statistical description of transport in this context is the following [42,43]: an ensemble of stochastic fields {φ(x, t)} with known Eulerian properties is considered to drive an associated ensemble of trajectories via the eq. ( 1).…”

“…The transport coefficients, diffusion and average velocity, are computed as simple statistical averages over the ensemble. DNS tries to mimic the whole (real) statistical problem resorting to numerical tools [42,43,45].…”