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The maximum stable pedestal pressure has been shown to increase with core pressure and in combination with profile stiffness this can lead to a positive feedback mechanism. However, the effect is shown to saturate for high β in ASDEX-Upgrade [1]. This paper investigates whether this effect appears in ITER scenarios, using ideal MHD numerical codes HELENA and MISHKA for different ITER scenarios from inductive 7.5-15 MA plasmas to steady-state scenarios at 10 MA. No pedestal pressure saturation is found for inductive scenarios; on the contrary for the 10MA steady-state scenario the pedestal pressure is the same for a wide range of total β and is limited by low n kink-peeling modes. Finally, a comparison of the achievable pressure for various levels of core profile stiffness is made with the IPB98(y,2) scaling law.

Edge localised modes (ELMs) are magneto-hydrodynamic (MHD) instabilities that drive filamentary plasma eruptions in high confinement tokamak discharges [1]. Gaining an improved understanding of ELMs is important [2]; in future fusion reactors such as ITER, ELM heat fluxes will need to be limited to ensure durability of divertor materials [3]. A new divertor configuration, the Super-X, will be tested on the MAST-U tokamak. The Super-X has a closed divertor designed to retain neutrals and could offer a solution for divertor heat flux control due to the increased connection length and magnetic flux expansion [4]. The effect of the new magnetic configuration on ELMs is unknown. First simulations of ELM dynamics in MAST-U plasmas are presented using the nonlinear MHD code JOREK [5], which is being developed to establish quantitative validation against current experiments [6]. The evolution of a model MAST-U plasma has been simulated, showing filamentary structures of higher density forming in the nonlinear phase. The simulations predict energy and particle losses that are compared with data from previous MAST experiments. A fluid neutrals model has been implemented in JOREK and will be presented, including the impact on ELM dynamics in MAST-U, considering configurations with varying divertor leg length.

The JOREK [1] MHD code is coupled to a newly developed particle tracer to simulate heavy impurity radiation and other effects. Particle-fluid sputtering, needed as boundary condition, as well as neoclassical transport is implemented and verified. We show that W sputtering, transport and radiation need to be coupled with MHD for accurate simulation.

Introduction The theory of magnetohydrodynamics (MHD) is valuable because it leads to baseline considerations for toroidal magnetic configurations, even when the parameter ranges in which these configurations are situated often don’t strictly satisfy the assumptions behind the MHD theory. The reason for this lies in the strong anisotropy of these configurations, where the dynamics perpendicular to the magnetic field lines is often indeed well-described by the theory, even though the direction parallel to the magnetic field lines is not. This work is situated in the study of fluted or high-n modes, which are normal modes that fit in the theory of MHD stability, that show very fast variation accross the magnetic field lines, as compared to the behavior along them. High-n MHD stability is important by itself as it can describe phenomena that are known to be important for the current and next generation of nuclear fusion devices, such as ELMs, which can be interpreted as due to two types of high-n instabilities: ballooning modes and peeling modes. In the view of studying these phenomena in enough detail, the two ingredients that this work combines within the world of high-n stability are the inclusion of a possible vacuum perturbation, which is necessary for peeling modes to exist in the absence of resistivity; and the correct treatment of 3-D effects, which are important not only for stellarators, but also for tokamaks. An example thereof can be found in the well-known consequences that toroidal field (TF) ripples can have on confinement [Sai+07; Wey+17]; but also in the application of resonant magnetic perturbation (RMP) coils to control ELMs by destabilizing them [Eva+06]. After briefly summarizing the theory of ideal linear 3-D MHD stability and the advancements of the PB3D (Peeling-Ballooning in 3-D) code over the past year in 2, this work then treats its application to the study of 3-D ballooning stability when applying RMPs in tokamaks in 3 and 4. Finally, in section 5, conclusions are phrased as well as the plans for future work.

The use of Resonant Magnetic Perturbation (RMP) coils is as an experimental technique for mitigating or suppressing large Edge Localized Modes (ELMs) in a number of tokamaks. In this work, we introduce a newly developed extension of the EBdyna_go code (introduced in [1]) that was designed to resolve the full-orbit of charged particles, in a collisionless manner. The new version of the code allows to study motions in the 3D perturbed fields generated by RMPs. This field can be calculated by a Biot-Savart solver or an integrated MHD code such as MARS-F [4]. The model has been applied on the COMPASS tokamak, comparing it with its RMP experimental database [2]. In particular we have focused here in the modelling of a High-Field-Side (HFS) RMP experiment with a dominant n=2 toroidal mode number.

Sufficient decrease of plasma pressure, ion and heat flux along the scrape-off layer of a tokamak fusion reactor are imperative to ensure the survival of the divertor tiles. This specific condition, defined as detachment, occurs within low temperature, high density, highly recycling plasma that can also be realized in linear plasma devices such as Magnum-PSI [1]. In MagnumPSI, high recycling is achieved by utilizing differential pumping across three vacuum chambers. Experiments have been conducted to mimic detachment in the Magnum-PSI linear device by varying the neutral background pressure at the chamber of the recycling target via H2 gas puffing [2], while the hydrogen plasma source parameters are kept constant across the experiments. Numerical modelling is carried out to help gain further insights regarding the physics behind detachment. The experiments are benchmarked with a coupled fluid-kinetic approach using the B2.5- EUNOMIA code package [3]. EUNOMIA is a Monte Carlo neutral simulation optimized for linear geometry. Thomson scattering measurements without gas puffing are used as a plasma boundary condition at the source in the simulation, and the gas pressure in the target chamber will be varied. The resulting electron density and temperature simulated profiles near the target are compared with profiles measured in experiments. This paper presents the result of the benchmark tests, and identifies the collisional processes and other physical effects relevant to the detached plasma state

Introduction Edge localized modes (ELMs) are periodically occurring instabilities that cause fast relaxations of the strong edge pressure gradient in the high-confinement regime (H-mode) of tokamak fusion plasmas [1]. These crashes induce intense heat fluxes towards the divertor tiles. This is a major concern for future fusion devices like ITER [2]. To understand the nonlinear ELM dynamics, it is necessary to check the validity of the (potentially predictive) ELM models. This can be achieved by comparing modeling output to experimental results. One essential parameter for such a comparison is the structure of the ELM crash, i.e. the toroidal mode number n. Recent quantitative comparisons of n and other parameters of the ELM crash between the nonlinear code JOREK and results obtained on the ASDEX Upgrade tokamak (AUG) demonstrated the progress in understanding the ELM crash by nonlinear modeling [3]. Consequently, the next question that is tackled here is how the ELM characteristics change with peeling-ballooning critical parameters. We therefore introduce a database of 30 shots containing more than 2500 type-I ELM crashes on AUG and investigate how the structure size changes with plasma parameters, which enables a more detailed testing of the codes in the future.

Plasma, as a non-linear medium supporting a rich and diverse range of electromagnetic and electrostatic oscillations, can enable a range of multi-wave interactions when excited by multiple injected propagating electromagnetic waves. Electromagnetic wave injection plays a dominant role in the introduction of energy in laser plasma interactions and in the heating of magnetically confined fusion reactors. In magnetically confined plasma, the EM waves tend to fall in the RF to microwave range, whilst in laser plasma interactions the signals are typically near the optical part of the spectrum.