Modeling of divertor particle and heat loads during application of resonant magnetic perturbation fields for ELM control in ITER

Abstract

First results from three-dimensional modeling of the divertor heat and particle flux pattern during application of resonant magnetic perturbation fields as ELM control scheme in ITER with the EMC3-Eirene fluid plasma and kinetic neutral transport code are discussed. The formation of a helical magnetic footprint breaks the toroidal symmetry of the heat and particle fluxes. Expansion of the flux pattern as far as 60 cm away from the unperturbed strike line is seen with vacuum RMP fields, resulting in a preferable heat flux spreading. Inclusion of plasma response reduces the radial extension of the heat and particle fluxes and results in a heat flux peaking closer to the unperturbed level. A strong reduction of the particle confinement is found. 3D flow channels are identified as a consistent reason due to direct parallel outflow from inside of the separatrix. Their radial inward expansion and hence the level of particle pump out is shown to be dependent on the perturbation level.______________________________________

3D effects of edge magnetic field configuration on divertor/scrape-off layer transport and optimization possibilities for a future reactor

“…3D numerical simulation has shown that in the case of an X-point poloidal divertor tokamak with an MP, for example DIII-D and ITER, the counter-streaming flows also appear, as shown in figure 8. The figure plots the Mach number distribution of ITER with an MP [29]. It is noted that for the case of ITER, it has been shown that the strong magnetic shear deforms the flux tubes significantly and reduces λ m down to several cm at the high field side and the top of the plasma [29], as shown in figure 8.…”

“…For the process of loss of parallel momentum, we consider a frictional interaction between counter-streaming flows, which are created in the edge region due to the magnetic field structure. It is found, from the numerical simulations in various devices, that the counter-streaming flow are formed not only in island divertors, but also in the stochastic layer of LHD [63], TEXTOR-DED [105], Tore Supra [111], DIII-D [112] and ITER [29]. It is also found that all these flow structures are regulated by the main poloidal mode number, m, of the perturbation field in the poloidal cross-section.…”

“…In helical devices, the situation might be even more complex compared to the 2D axi-symmetric tokamaks because of the 3D non-axi-symmetric magnetic field and divertor/first wall structure [12][13][14][15][16][17][18][19]. Complexity also appears in tokamaks with the application of symmetry-breaking magnetic perturbation (MP) fields aimed at edge transport control [20][21][22][23][24][25][26][27] or at edge localized mode mitigation or suppression [25,[28][29][30][31][32][33][34][35][36][37][38][39][40][41]. In tokamaks, the non-axi-symmetric magnetic field structure appears also due to intrinsic 3D fields (error fields, test blanket modules), due to 3D effects such as neoclassical tearing modes, non-axi-symmetric particles, energy and momentum sources, and 3D plasma-facing component geometry.…”

Non-linear magnetohydrodynamic modeling of plasma response to resonant magnetic perturbations

“…Models of plasma response based on a simplified assumption of screening currents on resonant surfaces [39] or on a linear MHD model [40] predict significant shortening of the lobes when the RMP is screened by the plasma response. Shortening is observed in the magnetic field topology [38][39][40] and through the reduction of fluxes [41,42] and generally increases with the increase of the width of the plasma region where the RMP is screened [39]. The shortening of lobes currently represent the most convenient way to quantify experimentally the screening of RMPs.…”

Non-linear modeling of the plasma response to RMPs in ASDEX Upgrade

“…However the conditions to obtain a strong mitigation or complete ELM suppression have been proven to be more complicated than this simple picture, due to the strong screening of RMPs by plasma flows. Even though the understanding of the plasma response to RMPs has been much improved in recent years [13][14][15][16][17][18][19][20][21][22][23][24], the interaction between plasma and RMPs has to be further studied to better interpret the current experiments and to be capable to predict the effect of RMPs in ITER. In particular, in addition to the resonant response, the role of the so-called 'edge kink response' or 'peeling response' has to be assessed, where the amplification of the external field perturbation is observed, probably resulting from the interaction between the applied perturbation and a marginally stable kink mode [25].…”