Max Planck Institute for Plasma Physics

In this work, we provide a full map of scattering scenarios between a Nielsen-Olesen vortex and antivortex. Importantly, in the deep type II regime, such a collision reveals a chaotic pattern in the final state formation with bounce windows immersed into annihilation regions. This structure is due to the energy transfer mechanism triggered by a quasinormal mode , specifically the Feshbach resonant mode , hosted by the vortex.

For future fusion devices, tungsten is the main candidate materials for the application as plasma facing materials (PFMs). However, considering the challenging operational condition with high thermal loading/thermal stress combining plasma exposure and neutron irradiation/embrittlement, one of the major concern for tungsten as PFMs is its intrinsic brittleness. To avoid cracking and components failure, toughening tungsten is widely investigated, among which tungsten fiber reinforced tungsten composites (W f /W) are developed using an extrinsic toughening mechanism. Recently, a new type of aligned long fiber W f /W (L-W f /W) with dedicated weak interface have been prepared by powder metallurgy process, combing the advantages of superb damage resilience with a much easier production compared to conventional chemical vapor deposition process. In this work, the newly developed material is characterized, including, mechanical tests, high heat flux tests, exposure to plasma for erosion and fuel retention tests. The l -W f /W composite could improve significantly the damage resilience compared to pure W without altering much of other properties.

• Adoption of object-oriented programming in gyrokinetic particle simulations, supporting scalable studies involving multiple species. • The implementation of a high-order piecewise field-aligned finite element method and a mixed particle-in-cell-particle-in-Fourier method within an electrostatic gyrokinetic particle simulation model, enabling efficient 3D and 2D simulations of tokamak plasmas. • A rigorous strong-form treatment of the gyrocenter equations of motion, enhancing accuracy and enabling filter- and buffer-free simulations. • A novel cache optimization strategy, delivering up to a tenfold speedup in specific simulation cases. • Support for unstructured meshes, facilitating whole-device simulations with complex geometries. The features of the TRIMEG-GKX code are described with emphasis on the exploration using novel/different schemes compared to other gyrokinetic codes, particularly the use of object-oriented programming, filter/buffer-free treatment, and a high-order piecewise field-aligned finite element method. The TRIMEG-GKX code solves the electromagnetic gyrokinetic equation using the particle-in-cell scheme, taking into account multi-species effects and shear Alfvén physics. The mixed-variable/pullback scheme has been implemented to enable electromagnetic studies. This code is parallelized using particle decomposition and domain cloning among computing nodes, replacing traditional domain decomposition techniques. The applications to study the micro- and macro-instabilities are demonstrated, including the energetic-particle-driven Alfvén eigenmode, ion temperature gradient mode, and kinetic ballooning mode. Good performance is achieved in both ad hoc and experimentally reconstructed equilibria, such as those of the ASDEX Upgrade (AUG), Tokamak á configuration variable (TCV), and the Joint European Torus (JET). Future studies of edge physics using the high-order C 1 finite element method for triangular meshes in the TRIMEG-C1 code will be built upon the same numerical methods.

Boron (11B) pellet injection is designated as a routine fueling technique for the EHL-2 spherical torus. The predictive modeling of 11B pellet injection for H-mode plasma fueling in EHL-2 has been performed using the three-dimensional (3D) nonlinear magnetohydrodynamic (MHD) code JOREK. The simulation results show that the 11B pellet induces rapid local cooling and temperature profile contraction. This constrains the ablation rate to a relatively low level, enabling it to penetrate effectively through the pedestal region and reach the core up to a position of 0.35 in normalized poloidal flux. After the pellet is completely ablated, approximately 90% of the 11B is deposited inside the separatrix. The increased edge resistivity resulting from temperature contraction modifies the poloidal magnetic flux via Ampère’s law. This perturbs the toroidal current density near rational surfaces, enhances the radial gradient therein and drives multiple tearing modes. Interactions among high poloidal mode (high-m) edge magnetic islands lead to magnetic stochasticity, but the stochastic layer does not expand inward beyond the pedestal during injection. After complete ablation, the growth of tearing modes ceases, suggesting that pellet injection can deliver material deeply without triggering persistently growing MHD instabilities.

The near-axis theory for quasi-isodynamic stellarator equilibria is reformulated in terms of geometric inputs to allow greater control of the ‘direct construction’ of quasi-isodynamic configurations and to facilitate understanding of the space of such equilibria. This includes a method to construct suitable magnetic axis curves by solving Frenet–Serret equations and an approach to controlling magnetic surface shaping at first order (plasma elongation), which previously has required careful parameter selection or additional optimisation steps. The approach is suitable for studying different classes of quasi-isodynamic stellarators including different axis ‘helicities’ and topologies (e.g. knotted solutions), and as the basis for future systematic surveys using higher order near-axis theory. As an example application, we explore a family of configurations with per-field-period axis helicity equal to one half, demonstrating an approximate scaling symmetry relating different field period numbers.

Predicting turbulent transport across the edge and scrape-off layer (SOL) is critical for the development of magnetic confinement fusion devices, including tokamaks and stellarators. However, first-principles full-f gyrokinetic (GK) simulations remain challenging due to complex magnetic geometries and their prohibitive computational cost. The high-performance full-f GK code GENE-X was specifically designed to overcome these challenges. Recently, a major computational acceleration was achieved through the implementation of a velocity-space spectral method, reducing the computational footprint by more than an order of magnitude. This breakthrough enables advanced first-principles studies of larger devices and high-confinement regimes, such as H-mode. Leveraging this new capability, we first present spectral simulations of L-mode plasmas in TCV. The new approach is validated through a detailed comparison with previously benchmarked grid-based simulations, showing excellent agreement in outboard midplane profiles, turbulence characteristics, and power balance. In this case, a computational speedup of nearly 50× is achieved. We then simulate the pre-L–H transition phase in AUG, focusing on a hydrogen discharge. As the L–H transition is approached, a region of strongly sheared radial electric field (Er) develops near the separatrix. Force-balance analysis reveals that the Er well is dominated by turbulence-driven poloidal flows. The turbulence is characterized by structures propagating in the electron diamagnetic direction, associated with electron drift waves and trapped-electron-mode turbulence. Notably, the predicted ion heat flux across the edge—a key quantity for L–H transition predictions—shows good quantitative agreement with experimental measurements. The role of turbulence-driven poloidal flows in shaping the Er well and their implications for H-mode access are further illustrated through comparisons of favorable and unfavorable configurations in AUG and TCV, validated against experiments. Overall, these results demonstrate that the spectral approach implemented in GENE-X provides a powerful and reliable first-principles predictive tool for turbulent transport studies in reactor-relevant scenarios, including ITER.

• Automation is based on modular finite state machines for process and safety control. • Interlock groups ensure safe gas handling during B₂D₆ plasma operation. • Automation significantly reduces the workload of the boronization operation team. • Process-critical events are synchronized via global control byte. High performance operation of magnetic confinement fusion reactors requires conditioning of the plasma-facing components by boronization [ 1] . This boron hydride layers traps residual oxygen in the vacuum vessel, thereby reducing radiation losses and, especially in metal components, mitigating sputtering by oxygen ions. Technically, at ASDEX Upgrade this coating is formed by a glow discharge process, using 10 % deuterated diborane (B 2 D 6 ) in helium as carrier gas (hereafter referred to as the “B₂D₆/He mix”). In this publication, we report on the complex software architecture, which was generally realized in the form of finite state machines (FSM). These state machines contain the entire process control of the boronization process, incorporating all the safety interlocks stored in a locking matrix. With this new procedure, the boronization can be carried out within 6 h on a normal working day, without the need to evacuate the office buildings adjacent to the experimental hall.

TCV is a medium sized tokamak equipped with a large suite of plasma diagnostics, a versatile array of poloidal shaping coils, an electron cyclotron heating system, and a two source neutral beam injection (NBI) system. The NBI system is capable of a simultaneous injection of energetic neutrals in the co-and counter-current directions. The resulting fast ion (FI) populations are used to study a multitude of FI-driven instabilities. While plasma instabilities in the below 1 MHz frequency range can be observed via standard diagnostics such as soft x-ray detectors, magnetics, fast ion loss detectors, and reflectometers, fluctuations in the range of >10 MHz require a specialized diagnostic. For this purpose the TCV tokamak has been equipped with a dedicated ion cyclotron emission (ICE) diagnostic, following a similar approach to AUG [1] and W7-X [2]. The diagnostic consists of a pair of magnetic coils (8 turns, 177 nH, 16 mm long, 7 mm in diameter), oriented orthogonally to each other to detect magnetic field fluctuations in the toroidal and poloidal directions. The coils are housed in a stainless steel electrostatic shield with a slit and are installed on the torus low field side at the midplane location, behind graphite protection tiles. The coil electric outputs are routed to the vacuum feedthroughs via a pair of coaxial cables, at which point one of the outputs is grounded at the feedthrough, from the airside. The second output is then routed to a rectifying radio frequency wave detector and a fast digitizer in the diagnostics rack. The rectifying detector is sensitive to signals in the 10-100 MHz frequency range and can measure the signal amplitude and the phase difference between the two probes, while the frequency information of the signal is lost. The benefit of this detection method is that the output signal can be digitized at a “slow” speed (200 kHz in the case of TCV) with a low cost digitizer and the data volume per plasma discharge is low. The fast digitizer, on the other hand, preserves the frequency information, albeit with a larger data volume. For the case of TCV, a 250 MHz sampling rate digitizer has been temporarily used, while a dedicated 1 GHz digitizer is currently being implemented. First results of high frequency (>10 MHz) instabilities detected in the presence of energetic ions will be presented.