Influence of molecular dissociation on blob-induced atom density perturbations

Abstract

The effects of enhanced electron and ion pressure perturbations mediated in filamentary structures (blobs) on the densities of neutral atoms and molecules are investigated through a self-consistent dynamical fluid model for plasma and neutral fields. The electron and ion densities and pressures, and the generalized vorticity, are simulated by a 2D drift-fluid model in an edge and scrape-off layer slab domain of a toroidally magnetically confined plasma. The plasma dynamics are coupled with a diffusion model for densities of neutral atoms and molecules. The combined model allows for determining the response of the density of neutrals with various temperatures to blobs. It is found that blobs locally deplete densities of molecules and atoms that do not originate from dissociation of molecules, whereas the density of atoms created by dissociation may increase during blob events. The neutral species, their temperature, and origin should thus be taken into consideration when estimating the effect of blobs on neutral density perturbations when calculating emission rates, e.g., for gas puff imaging.

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.…”

A self-consistent multi-component model of plasma turbulence and kinetic neutral dynamics for the simulation of the tokamak boundary

“…From Eqs. (31)(32)(33)(34)(35) and following the approach described in [52], a system of five equations for 𝜕 s 𝑛 D + , 𝜕 s 𝑛 D + 2 , 𝜕 s 𝑣 D + and 𝜕 s 𝑣 D + 2 , 𝜕 s 𝜙 is hence obtained for the interface between the CP and the MP border, considering the 𝜇 1 limit and isothermal ions and electrons. For this purpose, at the MP entrance, gradients along the 𝑥 direction are assumed weaker than gradients along 𝑠 by a factor 𝜖 = 𝜌 s0 /𝐿 n 𝜌 s0 /𝐿 T e 𝜌 s0 /𝐿 𝜙 1, with 𝐿 n , 𝐿 T e and 𝐿 𝜙 respectively the scale lengths of 𝑛 e , 𝑇 e and 𝜙 along the 𝑥 direction.…”

“…Progress was also made by coupling the two-dimensional fluid code HESEL [26] with a one-dimensional fluid-diffusive model for the neutral particles, which accounts for both atomic and molecular species. The resulting nHESEL [33,26,34] code thus allows for the simulation of a single-ion plasma including the interactions with three neutral species: cold hydrogen molecules puffed into the system, warm atoms resulting from the dissociation of the hydrogen molecules and hot hydrogen atoms generated by charge-exchange processes. Such a model was used to study the plasma fueling in the presence of gas puffs and the formation of a density shoulder in the tokamak boundary at a high gas puffing rate.…”

A self-consistent multi-component model of plasma turbulence and kinetic neutral dynamics for the simulation of the tokamak boundary

“…Progress was also made by coupling the two-dimensional fluid code HESEL [26] with a one-dimensional fluid-diffusive model for the neutral particles, which accounts for both atomic and molecular species. The resulting nHESEL [26,33,34] code thus allows for the simulation of a single-ion plasma including the interactions with three neutral species: cold hydrogen molecules puffed into the system, warm atoms resulting from the dissociation of the hydrogen molecules and hot hydrogen atoms generated by charge-exchange processes. Such a model was used to study the plasma fueling in the presence of gas puffs and the formation of a density shoulder in the tokamak boundary at a high gas puffing rate.…”