Plasma particle sources due to interactions with neutrals in a turbulent scrape-off layer of a toroidally confined plasma

Abstract

The conditions in the edge and scrape-off layer (SOL) of magnetically confined plasmas determine the overall performance of the device, and it is of great importance to study and understand the mechanics that drive transport in those regions. If a significant amount of neutral molecules and atoms is present in the edge and SOL regions, those will influence the plasma parameters and thus the plasma confinement. In this paper, it is displayed how neutrals, described by a fluid model, introduce source terms in a plasma drift-fluid model due to inelastic collisions. The resulting source terms are included in a four-field drift-fluid model, and it is shown how an increasing neutral particle density in the edge and SOL regions influences the plasma particle transport across the last-closed-flux-surface. It is found that an appropriate gas puffing rate allows for the edge density in the simulation to be self-consistently maintained due to ionization of neutrals in the confined region.

Scrape-off layer transport and filament characteristics in high-density tokamak regimes

“…As already mentioned, increasing investigatory efforts have been devoted to the role of neutrals in determining the SOL profile flattening at high density, both from an experimental [8] and a numerical point of view [54,55,56,57]. In this respect an attempt to distinguish the behaviour of upstream SOL e-folding length with respect to the neutral pressure as measured at the midplane or in the divertor region in AUG has been carried out, and the results are shown in Figure 19.…”

Influence of molecular dissociation on blob-induced atom density perturbations

“…The plasma and neutral modules are coupled through the source terms, and the plasma and neutrals interact self-consistently through molecular dissociation, molecular assisted ionization, atomic ionization, and atomic charge exchange collisions with ions, i.e., the interactions in (4). The combined neutral-plasma model is denoted nHESEL and is described in detail in [10].…”

“…In addition to the neutral deuterium species described in the model in [10], a passive fluid model for neutral helium gas has been added to the code. The transport equations for the helium density is identical to that of D 2 , as the mass and temperature of the particles are assumed to be the same, i.e.,…”

“…The neutrals consist of both deuterium molecules, which are puffed into the system, and deuterium atoms originating from dissociation of the molecules. This model is explained in detail in [10]. In addition to this, a passive species of helium atoms is simulated to highlight the difference between neutral atoms that are created from volume dissociation of molecules, and those which enter the system as atoms.…”

A reduced model of neutral-plasma interactions in the edge and scrape-off-layer: Verification comparisons with kinetic Monte Carlo simulations

“…The fluid-neutral models include those of Bisai and Kaw [19] (BK) and a recent extension of the HESSEL model. [20] The GBS model [5] is the only reduced fluid-plasma coupling to kinetic (Boltzmann) neutrals, besides the one proposed here, of which we are aware.…”