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Using the well-validated GENE gyrokinetic code and a reduced fluid model, the authors show that externally applied E×B flow shear — normally expected to suppress turbulence — can instead dramatically increase heat transport when the imposed shear is comparable in magnitude to the self-generated zonal flow shear already present in the plasma. The mechanism is destructive interference: imposed shear disrupts the self-regulating zonal flow structures that ordinarily cap turbulent transport, causing a sharp transport spike before eventual quenching at higher shear. This matters because rotation-based confinement strategies used in current and planned devices must now account for this destabilizing intermediate regime, not just the well-understood suppression regime.

██████████ 0.9 turbulence-modeling Preprint

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Nonlinear gyrokinetic simulations of the STEP compact fusion pilot plant design reveal that a catastrophic transition to high heat flux occurs at a critical value of q²βe — a combination of safety factor and electron pressure — that lies below all linear stability thresholds. The transition is governed by a balance between electrostatic and magnetic-flutter stresses, meaning standard linear stability analysis would incorrectly predict the plasma as safe. For STEP and similar high-beta designs, this implies that performance projections based purely on linear stability are optimistic, and nonlinear simulations are required to set operational limits.

██████████ 0.9 turbulence-modeling Preprint

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GyroFlow is a generative AI model that learns to directly sample from the saturated turbulent state of a 5D gyrokinetic plasma simulation, bypassing the computationally expensive transient evolution that normally consumes most of the simulation time. By treating ensembles of turbulent snapshots as equivalent to long time averages (ergodicity), the model achieves a substantial speedup over full simulations while outperforming other surrogates including the quasilinear models (QuaLiKiz, TGLF) currently used in integrated plasma modelling. This approach could make turbulence-aware whole-device modelling computationally tractable, with code available on GitHub.

██████████ 0.9 turbulence-modeling Preprint

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Full-f gyrokinetic simulations — the most physically complete approach to modelling edge plasma turbulence — suffer from large spurious oscillations (geodesic acoustic modes) at startup when initialized with a simple Maxwellian distribution, wasting significant compute time before meaningful physics emerges. This paper shows that pre-relaxing the initial distribution with a fast axisymmetric neoclassical simulation suppresses these transients substantially, particularly in the steep-gradient edge region relevant to H-mode pedestals. Validated on the ASDEX Upgrade tokamak, the method reduces noise and accelerates convergence without additional physics assumptions.

██████████ 0.9 turbulence-modeling Preprint

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A systematic comparison of 37 boronized-wall versus 48 lithium-conditioned-wall discharges on EAST shows that boronization opens a much wider density operating window for I-mode (Greenwald fraction 0.26–0.77 vs 0.35–0.54) and increases access to the energetically favorable magnetic configuration from 8% to 51% of discharges. The favorable configurations also show deeper radial electric field wells and stronger velocity shear, which suppresses turbulence. I-mode is a promising confinement regime because it maintains good energy confinement without the large ELMs that threaten divertor components, and this result suggests wall conditioning is a practical lever for accessing it reliably.

██████████ 0.9 elm-control Preprint

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Gyrokinetic parameter scans across the Cyclone Base Case and the ST40 spherical tokamak show that as the product q²βe (safety factor squared times electron beta) crosses a critical threshold, Maxwell stress from electromagnetic fluctuations suppresses zonal flow generation, causing turbulent transport to diverge. Crucially, this threshold is below all linear stability limits — meaning the plasma transitions to a high-transport state via a nonlinear mechanism invisible to conventional stability analysis. This independently corroborates the STEP result and the E×B shear destabilization finding, pointing to a consistent picture of nonlinear electromagnetic transport transitions at high beta.

██████████ 0.9 turbulence-modeling Preprint

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Runaway electrons generated during plasma disruptions travel through chaotic magnetic field regions, and this paper shows their escape is non-diffusive: rather than exponential decay assumed by the standard Rechester-Rosenbluth model, particles trapped near magnetic islands produce a power-law escape tail due to 'sticky' chaotic dynamics. The new model is validated against both an analytical map for the TBR-1 tokamak and full 3D MHD disruption simulations of JET using JOREK. Better runaway transport models are critical for predicting wall loading and designing mitigation strategies in ITER, where runaway beam energies can reach tens of MeV.

██████████ 0.9 plasma-disruption Preprint

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Laser-driven D-D neutron sources are being developed as bench-scale surrogates for fusion neutron environments to test tritium breeding blankets, but this study shows their neutron spectra differ substantially from the idealized 2.45 MeV isotropic assumption — and this matters enormously: the real spectrum changes tritium production per neutron by −2.5% to +54.1% depending on blanket geometry, driven almost entirely by spectral rather than directional effects. Using coupled PIC, nuclear reaction, and Monte Carlo neutron transport calculations, the authors quantify exactly how misleading isotropic-source experiments can be. This work is directly relevant to qualification testing of lithium ceramic and liquid metal blanket modules before DEMO.

██████████ 0.9 tritium-breeding Preprint

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A new neoclassical transport module for the NLT gyrokinetic code is validated against the established NEO code across a wide collisionality range, including three-species plasmas with carbon impurities relevant to the EAST tokamak. The module introduces a composite substep integration scheme that handles large macroscopic time steps accurately, and a direct steady-state solver that avoids long relaxation runs. Impurity transport control is essential for fusion because high-Z impurities like tungsten radiate strongly and can quench the plasma; having validated multi-species neoclassical tools integrated into gyrokinetic codes enables more realistic transport modelling.

██████████ 0.8 turbulence-modeling Preprint

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By reducing current in specific coils of the HSX and W7-X stellarators, this computational study shows that giant magnetic island chains can be created at the plasma edge, producing straight X-point legs that channel exhaust plasma directly to plasma-facing components. Unlike the complex helical divertor normally used in stellarators, these configurations offer a geometrically simpler exhaust pathway that may be easier to engineer. Heat load calculations using EMC3-Lite confirm the feasibility, making this relevant to the outstanding challenge of power exhaust in non-axisymmetric fusion devices.

██████████ 0.8 divertor-thermal Preprint

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