arXiv subjects

the JOREK Team

Publications and source records attributed to the JOREK Team.

6 recordsLinked to original sources

arXiv2026

Hybrid Kinetic-MHD Simulations of Drift-Orbit Effects on the Stability and Non-Linear Dynamics of Runaway Electron Beams

During tokamak disruptions, the Ohmic current may be replaced by a non-inductive runaway electron (RE) current, affecting resistive stability. Previous studies suggest that, in the linear phase, the presence of REs acts destabilizing for tearing modes (TM) compared to a scenario with Ohmic current. In the non-linear regime, this translates to larger saturation amplitudes. These results are based on the assumption of zero drift-orbit deviation from the magnetic flux surfaces corresponding to the low-energy limit. This work investigates the importance of this kinetic effect by studying the linear and non-linear TM dynamics in RE beams with different RE energies, providing a clear picture of finite-orbit-width (FOW) effects. We use a hybrid fluid-kinetic model in the 3D non-linear magnetohydrodynamic (MHD) code JOREK, treating REs kinetically with a full-f Monte Carlo approach in self-consistent interaction with the MHD mode dynamics. The study shows that the presence of REs modifies the characteristics of the instability in several ways. First, we find that the major-radial displacement of drift orbits from flux surfaces induces an $m=1$ perturbation to the equilibrium current, introducing additional mode coupling between $(m,n)$ instabilities and the $(m\pm1,n)$ sidebands. Second, we find that increasing RE energy has a stabilizing effect on the MHD modes because REs cannot support narrow current sheets on rational flux surfaces owing to the drift-orbit displacement. This counteracts the destabilizing effect that REs have on TMs in the low-energy limit. For the scenario investigated, the stabilizing effect dominates over the additional mode coupling, reducing the development of stochastic magnetic regions with increasing RE energy and thereby lowering radial particle transport. Overall, we find that FOW effects can substantially alter the MHD stability and non-linear dynamics of RE beams.

physics.plasm-ph↗

arXiv2026

JOREK simulations of the X-point radiator formation and its movement in ASDEX Upgrade

Future large-scale magnetic confinement fusion reactors require operational regimes that can avoid extreme heat fluxes onto the plasma-facing components. One promising regime is the X-point radiator (XPR), which relies on a highly radiative, cold and dense plasma volume forming above the X-point, and which can be accessed via impurity seeding. Experimentally, the height of the XPR can be controlled by adjusting the seeding rate and heating power. This contribution presents axisymmetric (2D) simulations of the XPR regime in ASDEX Upgrade using the nonlinear MHD code JOREK extended with a kinetic particle framework for the main species neutrals and nitrogen impurities. With the time-dependent simulations, the progression from attached divertors to a complete detachment with the XPR formation is shown, highlighting the effects of the neutrals and impurities separately. Amidst this progression, the formation and the loss of the high-field-side high-density are observed. After the XPR is well-formed at the height of 6.8 cm, the fuelling and seeding rates are adjusted so that the XPR remains stationary. From the stationary case, the seeding rate is then changed to see how the XPR location reacts. By increasing and decreasing the seeding rate, the XPR responds by moving upwards and downwards, respectively. These simulations show JOREK's capability of simulating time-varying XPR, which will provide a baseline for the transition to 3D simulations, so the MHD activities and their interaction with the XPR can be studied.

physics.plasm-ph↗

arXiv2026

Quantitative 3D non-linear simulations of shattered pellet injection in ASDEX Upgrade using JOREK

Shattered pellet injection (SPI) as primary mitigation method for major disruptions in ITER has a large parameter space available for optimization including the total amount of injected material, the size of the individual pellet fragments, the material composition, and the timing of multiple injections. This flexibility needs to be exploited to simultaneously minimize thermal heat loads, electromagnetic vessel forces, and formation of relativistic electrons and their impacts on plasma facing components. In this article, we apply 3D non-linear magnetohydrodynamic modelling to SPI experiments in the ASDEX Upgrade tokamak, going beyond our previous work [Tang et al Nucl. Fusion 65 116003 (2025)] by resolving some discrepancies between simulations and experiment and thus opening the path to quantitative model validation and experiment interpretation. The key element that enables the transition from merely qualitative comparisons to quantitatively reliable predictions of the thermal quench duration and the radiation fraction is the incorporation of a simplified treatment of parallel heat-flux limiting. The work increases the confidence of matching the key processes of disruption mitigation with this high fidelity modelling in view of predictive studies for ITER.

physics.plasm-ph↗

arXiv2025

Non-linear MHD modelling of shattered pellet injection in ASDEX Upgrade

Shattered pellet injection (SPI) is selected for the disruption mitigation system in ITER, due to deeper penetration, expected assimilation efficiency and prompt material delivery. This article describes non-linear magnetohydrodynamic (MHD) simulations of SPI in the ASDEX Upgrade tokamak to test the mitigation efficiency of different injection parameters for neon-doped deuterium pellets using the JOREK code. The simulations are executed as fluid simulations, while additional marker particles are used to evolve the charge state distribution and radiation property of impurities based on OpenADAS atomic data, i.e., a collisional-radiative model is used. Neon fraction scans between 0 - 10% are performed. Numerical results show that the thermal quench (TQ) occurs in two stages. In the first stage, approximately half of the thermal energy is abruptly lost, primarily through convective and conductive transport in the stochastic fields. This stage is relatively independent of the neon fraction. In the second stage, where the majority of the remaining thermal energy is lost, radiation plays a dominant role. In case of pure deuterium injection, this second stage may not occur at all. A larger fraction ($\sim $20%) of the total material in the pellet is assimilated in the plasma for low neon fraction pellets ($\leq 0.12\%$) due to the full thermal collapse of the plasma occurring later than in high neon fraction scenarios. Nevertheless, the total number of assimilated neon atoms increases with increasing neon fraction. The effects of fragment size and penetration speed are then numerically studied, showing that slower and smaller fragments promote edge cooling and the formation of a cold front. Faster fragments result in shorter TQ duration and higher assimilation as they reach the hotter plasma regions quicker.

physics.plasm-ph↗

arXiv2024

Implementation of matrix compression in the coupling of JOREK to realistic 3D conducting wall structures

JOREK is an advanced non-linear simulation code for studying MHD instabilities in magnetically confined fusion plasmas and their control and/or mitigation. A free-boundary and resistive wall extension was introduced via coupling to the STARWALL and CARIDDI codes, both able to provide dense response matrices describing the electromagnetic interactions between plasma and conducting structures. For detailed CAD representations of the conducting structures and high resolutions for the plasma region, memory and computing time limitations restrict the possibility of simulating the ITER tokamak. In the present work, the Singular Value Decomposition provided by routines from the ScaLAPACK library has been successfully applied to compress some of the dense response matrices and thus optimize memory usage. This is demonstrated for simulations of Tearing Mode and Vertical Displacement Event instabilities. An outlook to future applications on large production cases and further extensions of the method are discussed.

physics.plasm-ph↗

arXiv2024

Neural-Parareal: Dynamically Training Neural Operators as Coarse Solvers for Time-Parallelisation of Fusion MHD Simulations

The fusion research facility ITER is currently being assembled to demonstrate that fusion can be used for industrial energy production, while several other programmes across the world are also moving forward, such as EU-DEMO, CFETR, SPARC and STEP. The high engineering complexity of a tokamak makes it an extremely challenging device to optimise, and test-based optimisation would be too slow and too costly. Instead, digital design and optimisation must be favored, which requires strongly-coupled suites of High-Performance Computing calculations. In this context, having surrogate models to provide quick estimates with uncertainty quantification is essential to explore and optimise new design options. Furthermore, these surrogates can in turn be used to accelerate simulations in the first place. This is the case of Parareal, a time-parallelisation method that can speed-up large HPC simulations, where the coarse-solver can be replaced by a surrogate. A novel framework, Neural-Parareal, is developed to integrate the training of neural operators dynamically as more data becomes available. For a given input-parameter domain, as more simulations are being run with Parareal, the large amount of data generated by the algorithm is used to train new surrogate models to be used as coarse-solvers for future Parareal simulations, leading to progressively more accurate coarse-solvers, and thus higher speed-up. It is found that such neural network surrogates can be much more effective than traditional coarse-solver in providing a speed-up with Parareal. This study is a demonstration of the convergence of HPC and AI which simply has to become common practice in the world of digital engineering design.

physics.plasm-ph↗