Recent progress in the quantitative validation of JOREK simulations of ELMs in JET

Abstract

Future devices like JT-60SA, ITER and DEMO require quantitative predictions of pedestal density and temperature levels, as well as inter-ELM and ELM divertor heat fluxes, in order to improve global confinement capabilities while preventing divertor erosion/melting in the planning of future experiments. Such predictions can be obtained from dedicated pedestal models like EPED, and from non-linear MHD codes like JOREK, for which systematic validation against current experiments is necessary. In this paper, we show progress in the quantitative validation of the JOREK code using JET simulations. Results analyse the impact of diamagnetic terms on the dynamics and size of the ELMs, and evidence is provided that the onset of type-I ELMs is not governed by linear MHD stability alone, but that a nonlinear threshold could be responsible for large MHD events at the plasma edge.

Insights into type‐I edge localized modes and edge localized mode control from JOREK non‐linear magneto‐hydrodynamic simulations

“…The peak heat fluences in JET ELM simulations were compared for a large number of equilibria to the experimentally observed scaling. Simulations without background flows show excellent agreement regarding energy losses and peak heat fluences; however, they do not reproduce the distribution of heat between the inner and outer divertor legs of the experiments.…”

Analysis of ELM stability with extended MHD models in JET, JT-60U and future JT-60SA tokamak plasmas

“…In this section, the basic equations of the linear and nonlinear extended MHD stability codes, MINERVA-DI and JOREK, are introduced briefly; the details are written in [9] and [18], respectively.…”

“…The neutral beam injection (NBI) momentum, mass density, temperature, and current sources V NBI , r S , S T and j A have been introduced, where j A also includes the time-dependent bootstrap current calculated using Sauterʼs formula [21,22]. The perpendicular mass and thermal diffusivities D ⊥ and k^used in the simulations are ad hoc coefficients with a well at the pedestal region to represent the transport barrier, and the parallel thermal conductivity k  is expressed to follow the Braginskii one as k k = and k  T constant in the pedestal region [18], and D ⊥ and k^at y = 0.8 are assumed to be…”

Filamentary plasma eruptions and their control on the route to fusion energy

“…In an MHD model, this process is slow. Thus, even though simulations can reproduce the energy-loss mechanism and the filamentation relatively well, they typically exhibit a slightly lower rate of energy loss (approximately a factor of 2), which results in a longer duration of the ELM activity than that observed experimentally 46 . It is not yet clear which physics effect (or effects) that could accelerate the predicted ELM timescales is missing from current MHD simulation models, but we highlight two candidates.…”

“…In the past decade, much progress has been made, particularly in terms of pushing resistivity closer to the experimental conditions 45,46 . Results from a number of codes have added weight to the international consensus that type I ELMs are indeed a b linked to peeling-ballooning modes and that the filamentation of the edge plasma plays a major role in the nonlinear dynamics of the instability 47,48 .…”