Global migration of impurities in tokamaks

Abstract

Migration of impurities in tokamaks has been studied with the help of tracer-injection ( 13 C and 15 N) experiments in JET and ASDEX Upgrade since 2001. We have identified a common pattern for the migrating particles: SOL flows drive impurities from the low-field side towards the high-field side of the vessel. Migration is also sensitive to the density and magnetic configuration of the plasma, and strong local variations in the resulting deposition patterns require 3D treatment of the migration process. Moreover, re-erosion of the deposited particles has to be taken into account to properly describe the migration process during steady-state operations of the reactor.

Nitrogen retention in ASDEX Upgrade

“…The migration of impurities is a key process in the area of plasma-surface interaction, as it controls net erosion, material mixing, plasma contamination and tritium retention [1,2]. Nitrogen (N) is a convenient choice for migration studies for several reasons: First, it is tolerated by the plasma and easy to handle and to detect.…”

Influence of toroidal field ripple and resonant magnetic perturbations on global 13C transport in ASDEX Upgrade

“…The injection of the tracers was performed from a single valve located in an outer midplane port in the toroidal sector 9 of AUG (see Fig. 1 experiment and the associated modeling have been reported in detail in [1,8,9].…”

“…The ERO simulations resulted in a mean radial dissociation location of R À R sep ¼ 5:1 cm (R sep being the R coordinate of the low-field side primary separatrix) indicating that the majority of the 13 C + ions are born in the far-SOL and halo plasma regions. For a more detailed description, see [1,9].…”

“…The present understanding of global impurity migration in tokamaks is largely based on observations from experiments using tracers such as 13 C injected into the torus and marker tiles or probes exposed to the plasma [1]. When extrapolating these results to next-step devices, it is noticeable that the magnetic field in, e.g., ITER includes substantially more non-axisymmetric components than what is typically present in the experiments.…”

“…The transport of injected 13 C particles is simulated until their deposition corresponding to a tracer injection experiment carried out in 2011 [1,8]. Deposition patterns in axisymmetric and non-axisymmetric simulation cases are then compared to assess the significance of the non-axisymmetric features of the magnetic field.…”