arXiv subjects

Konrad Eder

Publications and source records attributed to Konrad Eder.

7 recordsLinked to original sources

arXiv2026

Turbulent Nature of the Quasicontinuous Exhaust Regime for Fusion Plasmas

We demonstrate a turbulence mechanism that reconciles high plasma confinement with efficient heat exhaust -- a central challenge for fusion energy. Global two-fluid turbulence simulations of the reactor-relevant Quasicontinuous Exhaust regime on the ASDEX Upgrade tokamak reveal that a quasicoherent mode drives mesoscopic oscillations of the pedestal boundary across the magnetic separatrix and ejects ballistic filaments (blobs), reproducing both the mean profiles and turbulent fluctuations observed experimentally. This behavior arises from a synergistic interplay between kinetic ballooning modes and resistive X-point modes straddling the separatrix. These first-principles results place extrapolations to future fusion reactors on a firm physical footing.

physics.plasm-ph↗

arXiv2025

The impact of plasma turbulence on atomic reaction rates in the detached ASDEX Upgrade divertor

Numerical modeling of the edge and scrape-off layer (SOL) must account for atomic processes such as hydrogenic ionization and recombination, charge-exchange, and line radiation. Their reaction rates depend non-linearly on density and temperature and are thus sensitive to turbulent fluctuations, whose inclusion/omission may significantly affect model outcomes. We quantify the impact of fluctuations by studying global turbulence simulations of the edge and SOL of ASDEX Upgrade in both attached and detached divertor conditions. While the effect of fluctuations is minimal for the attached state, pronounced localized discrepancies emerge in colder, detached conditions. The inclusion of turbulent fluctuations, when compared to mean-field calculations, causes a factor of 2 reduction in ionization and radiation rates local to the detachment front in the confined edge region. The effect arises from fluctuations crossing below the ionization energy threshold, facilitated by low mean temperature and increased fluctuation amplitudes at the detachment front. The rate reduction (rather than rate increase) is explained by the character of divertor fluctuations (negative density-temperature correlation, i.e., cold and dense blobs), notably distinct from characteristic fluctuations found at the outboard-midplane (positive correlation, i.e., hot and dense blobs). Furthermore, the cold and dense fluctuations enable efficient plasma recombination even at average temperatures above the recombination threshold. In detached conditions, the combined plasma particle source from ionization and recombination is, therefore, effectively reduced by at least 50% when compared to the standard mean-field source.

physics.plasm-ph↗

arXiv2025

On the mechanism of Pedestal Relaxation Events -- Insights gained by turbulence simulations with GRILLIX

Pedestal Relaxation Events (PREs) appear in I-mode discharges close to the I-H transition. Although they show certain similarities with Edge Localised Modes (ELMs), i.e. periodic energy ejections, the underlying mechanism seems to be very different from the mechanism responsible for ELMs. In this manuscript, we present global trans-collisional fluid simulations of an I-mode discharge in ASDEX Upgrade using GRILLIX. We observe multiple PREs during the simulation, which reproduce a range of experimentally observed PRE characteristics. Furthermore, a detailed analysis of various mode properties in our simulation allows us to pinpoint the underlying mechanism responsible for triggering PREs to Micro-Tearing Modes (MTMs). The system is analysed dynamically by evaluating density and electron temperature gradient lengths at the OMP position, where the MTM is located and grows over time. The path taken by the system in gradient length space is compared to a growth-rate estimate calculated by linear theory in simplified slab geometry, providing excellent agreement. Building on these insights, we sketch a qualitative picture of a full PRE cycle. Finally, we discuss the influence of the recently implemented Landau-fluid closure and the challenges of simulating low collisionality regimes with trans-collisional fluid models, like the one employed by GRILLIX.

physics.plasm-ph↗

arXiv2024

On the proper treatment of magnetic fluctuations in full-$f$ field-aligned turbulence codes

Plasma turbulence in the edge of magnetic confinement devices is customarily treated as full-$f$ due to large fluctuations. For computational efficiency, field-aligned coordinates are employed, separating the magnetic field into equilibrium $B_0$ and delta-f perturbations which are handled by the magnetic flutter operators. Evolving the full-$f$ pressure with delta-$f$ magnetic perturbations can cause inconsistency since the latter contain background components such as the Shafranov shift, which are actually parts of the equilibrium magnetic field. Such background components ($B_s$) contained in the magnetic perturbations undermine the field-aligned numerics when treated as flutter: errors arise if $B_s/B_0\ll l_\perp/h_\parallel$ is not satisfied, with the perpendicular turbulence scale $l_\perp$ and the parallel grid distance $h_\parallel$. We find that the commonly used removal of $B_s$ by subtracting the toroidal average of magnetic perturbations intervenes in the Alfv\'en dynamics, causing spurious $E\times B$ transport. Instead, we propose an improved method to dynamically filter out the evolving background from the turbulent magnetic fluctuations in the time domain. The filter is verified in both low and high confinement tokamak conditions, confirming its capability to preserve the turbulence fidelity, provided sufficient filter width.

physics.plasm-ph↗

arXiv2024

Tokamak edge-SOL turbulence in H-mode conditions simulated with a global, electromagnetic, transcollisional drift-fluid model

The design of commercially feasible magnetic confinement fusion reactors strongly relies on the reduced turbulent transport in the plasma edge during operation in the high confinement mode (H-mode). We present first global turbulence simulations of the ASDEX Upgrade tokamak edge and scrape-off layer (SOL) in ITER baseline H-mode conditions. Reasonable agreement with the experiment is obtained for outboard mid-plane measurements of plasma density, electron and ion temperature, as well as the radial electric field. The radial heat transport is underpredicted by roughly 1/3. These results were obtained with the GRILLIX code implementing a transcollisional, electromagnetic, global drift-fluid plasma model, coupled to diffusive neutrals. The transcollisional extensions include neoclassical corrections for the ion viscosity, as well as either a Landau-fluid or free-streaming limited model for the parallel heat conduction. Electromagnetic fluctuations are found to play a critical role in H-mode conditions. We investigate the structure of the significant $E \times B$ flow shear, finding both neoclassical components as well as zonal flows. But unlike in L-mode, geodesic acoustic modes are not observed. The turbulence mode structure is mostly that of drift-Alfv\'en waves. However, in the upper part of the pedestal, it is very weak and overshadowed by neoclassical transport. At the pedestal foot, on the other hand, we find instead the (electromagnetic) kinetic ballooning mode (KBM), most clearly just inside the separatrix. Our results pave the way towards predictive simulations of fusion reactors.

physics.plasm-ph↗

arXiv2023

Magnetic flutter effect on validated edge turbulence simulations

Small magnetic fluctuations ($B_1/B_0 \sim 10^{-4}$) are intrinsically present in a magnetic confinement plasma due to turbulent currents. While the perpendicular transport of particles and heat is typically dominated by fluctuations of the electric field, the parallel stream of plasma is affected by fluttering magnetic field lines. In particular through electrons, this indirectly impacts the turbulence dynamics. Even in low beta conditions, we find that $E\times B$ turbulent transport can be reduced by more than a factor 2 when magnetic flutter is included in our validated edge turbulence simulations of L-mode ASDEX Upgrade. The primary reason for this is the stabilization of drift-Alfv\'en-waves, which reduces the phase shifts of density and temperature fluctuations with respect to potential fluctuations. This stabilization can be qualitatively explained by linear analytical theory, and appreciably reinforced by the flutter nonlinearity. As a secondary effect, the steeper temperature gradients and thus higher $\eta_i$ increase the impact of the ion-temperature-gradient mode on overall turbulent transport. With increasing beta, the stabilizing effect on $E\times B$ turbulence increases, balancing the destabilization by induction, until direct electromagnetic perpendicular transport is triggered. We conclude that including flutter is crucial for predictive edge turbulence simulations.

physics.plasm-ph↗

arXiv2021

preCICE v2: A Sustainable and User-Friendly Coupling Library

preCICE is a free/open-source coupling library. It enables creating partitioned multi-physics simulations by gluing together separate software packages. This paper summarizes the development efforts in preCICE of the past five years. During this time span, we have turned the software from a working prototype -- sophisticated numerical coupling methods and scalability on ten thousands of compute cores -- to a sustainable and user-friendly software project with a steadily-growing community. Today, we know through forum discussions, conferences, workshops, and publications of more than 100 research groups using preCICE. We cover the fundamentals of the software alongside a performance and accuracy analysis of different data mapping methods. Afterwards, we describe ready-to-use integration with widely-used external simulation software packages, tests and continuous integration from unit to system level, and community building measures, drawing an overview of the current preCICE ecosystem.

cs.MS↗