On the Neutral Gas Localization in a Divertor Plasma

Plasma boundary phenomena in tokamaks

“…Models available for such work [485] include analytic formulations [412,[486][487][488][489][490][491][492] as well as test particle [493] and Monte Carlo codes [124,142,424,482,[494][495][496][497][498][499][500][501]. Fluid impurity codes [502][503][504][505][506][507][508][509][510], developed for divertor studies, could also be employed, but their assumption of high collisionality and instant thermalization of impurity ions is less applicable for limiter situations. More experimental measurements are required in well characterized SOLs, employing known calibrated impurity injections.…”

Impurity enrichment studies with induced scrape-off layer flow on DIII-D

“…The ionization mean free path of a recycling impurity atom is determined by the velocity of the impurity neutral and its ionization rate, which is in turn determined by the divertor parameters (in particular, the electron density and temperature). Neglecting electric field effects and cross-field transport, the two main forces acting on impurity ions in the SOL are the collisional thermal force and the frictional drag of the impurities with the background plasma [2,3]. Under what we will term 'natural' flow conditions (i.e., those without external augmentation of the flow in the SOL), the parallel flow of the bulk plasma ions in the SOL is small and is directed from the core plasma towards the divertor target.…”

Zero-dimensional relationships of tokamak scrape-off-layer parameters and the influence of these parameters on transport in the main plasma

“…In most sub-regions of the plane F s , Q s the dependence of the boundary density on the particle flux is in fact rising. Only in region 1.1.1 do we find n s ~ F; 1 " 18 [10,11,14,15]. In this case, on the curve Q VI (see Eq.…”

“…To describe the processes occurring in the SOL region of a tokamak, we use zero-dimensional integral equations which define the energy and particle flux balances in the plasma and neutral gas, parallel to and across the magnetic field. Also, since theoretical ideas about the behaviour of the wall plasma have become more abundant [8][9][10][11][12][13][14][15][16], the proposed model should describe, as far as possible, all the most important physical phenomena. These should include, in our opinion: the presence of a bifurcation transition between the low and high recycling regimes [8,9]; an N-shaped dependence of the characteristic plasma density in the SOL zone on the plasma temperature near the neutralizing plates for high recycling [10,11], which is due to the radiative energy loss channel; and ionization induced exclusion of the neutral component of the working gas in the recycling zone near the plates [12,13].…”

“…Also, since theoretical ideas about the behaviour of the wall plasma have become more abundant [8][9][10][11][12][13][14][15][16], the proposed model should describe, as far as possible, all the most important physical phenomena. These should include, in our opinion: the presence of a bifurcation transition between the low and high recycling regimes [8,9]; an N-shaped dependence of the characteristic plasma density in the SOL zone on the plasma temperature near the neutralizing plates for high recycling [10,11], which is due to the radiative energy loss channel; and ionization induced exclusion of the neutral component of the working gas in the recycling zone near the plates [12,13]. Undoubtedly, a very important factor is the impurity behaviour, which we shall consider phenomenologically.…”