Recent Publications

Pedestal penalty factors for ELM-free regimes in DIII-D and extension to fusion pilot plant design

Andrew Oakleigh Nelson, Tomas Odstrcil, Tim Slendebroek, Zeyu Li, Nils Leuthold, Carl Friedrich Benedikt Zimmermann, John Anthony Labbate, Jamie Dunsmore, Jacob Schellpfeffer, Severin Sebastian Denk, et al.

Though the EPED model, which provides a first-principles-based predictive capability for the pedestal height and width in H-mode tokamak plasmas, has been validated extensively in type-I edge-localized mode (ELM) regimes, significant uncertainties remain in predicting the height of the pressure pedestal in fusion pilot plants that must deploy ELM mitigation or suppression techniques. In this work, we compare the EPED1 NN surrogate to measurements from a broad dataset on the DIII-D tokamak, spanning ELMy, Small-ELM, QH-mode, Wide-Pedestal QH-mode, RMP-suppressed, I-mode, EDA H-mode, QCE and ELM-free NT scenarios. Using a robust Bayesian profile-fitting framework, we find that the measured pedestal pressure is systematically reduced relative to the EPED prediction in nearly all regimes, with regime-median pedestal pressures ranging from ∼93% of the predicted value in H-mode like regimes to below 40% in scenarios in which the edge region is governed by other transport mechanisms. We show that this deficit – termed a “pedestal penalty” – is not a fixed per-regime offset and that some scenarios recover toward the EPED prediction at high normalized pressure (β N ) and low pedestal collisionality (ν * e,ped ). While a simple scaling for the pedestal penalty can help illustrate model uncertainties on the DIII-D database, it misses key scenario-specific physics and should not be taken as a substitute for the development of predictive pedestal models for ELM-free FPPs. Uncertainties in FPP performance associated with a reduction of the pedestal height relative to EPED are quantified using the FUSE code, which shows that the achievable fusion power on ITER may be reduced by a factor of two if the pedestal is limited to 60% of the EPED prediction, a value well within the uncertainties observed on DIII-D. Further implications for FPP design are discussed, including the need for regime-dependent pedestal models that do not rely on a degraded EPED variant.

Simulation study of Li-pellet-triggered ELMs in EAST towards understanding small-ELM behavior of HFS Li-pellet injection

Mao Li, Zhen Sun, Huayi Chang, Yue Zhang, Dayu Zhou, T Y Xia, Jizhong Sun

Motivated by recent EAST experiments showing that Li pellet injection from the high-field side triggers much smaller ELMs than outer-midplane (OMP) injection, a BOUT++ three-field MHD model coupled with impurity effects has been employed to investigate how the poloidal injection angle affects the triggering and subsequent evolution of ELMs. To this end, two scenarios are considered, in which Li pellets are injected near the upper X-point from the low-field side (LFS-UP) and the high-field side (HFS-UP), respectively. The OMP simulation data obtained within the numerical framework established in our previous study are also included for comparison. The simulations show that the ELM-triggering threshold decreases as the poloidal injection angle shifts from the OMP toward the HFS; the trend is associated with the easier excitation of a low-n mode capable of reaching the amplitude required for ELM triggering. The subsequent ELM evolution also depends on the poloidal injection angle. In the LFS-UP scenario, the ELM undergoes phases of linear growth, fast crash, turbulent transport, and saturation, similar to that in the OMP scenario. In contrast, in the HFS-UP scenario, the nonlinear dominant mode is suppressed shortly after ELM onset by the stronger stabilizing effect of the pedestal E×B flow shear, leading to a negligible fast crash phase. Meanwhile, the inward spreading of the pressure perturbation is constrained near the pedestal top. The rapid mode suppression, together with the restricted inward spreading of the pressure perturbation, prevents the ELM from developing into a large crash. Accordingly, the HFS-UP scenario exhibits a parameter window for small pellets in which the triggered ELM causes a pedestal energy loss of about 0.1% or less. The present results provide a plausible physical explanation for the EAST observations.

Overview of the outcomes of the EUROfusion Enabling Research project on real-time reflectometry plasma tracking for next-generation machines

Filipe da Silva, Jorge Manuel Santos, António Silva, Jorge Ferreira, Emanuel Alves Ricardo, Stéphane Heuraux, Roland Sabot, Frederic Clairet, Yassir Moudden, Gianluca De Masi, et al.

Reflectometry is anticipated to play a significant role in plasma positioning, shaping, and tracking for DEMOnstration Power Plant (DEMO), potentially replacing magnetic diagnostics. We present an overview of the outcomes of the EUROfusion Enabling Research (EnR) project ENR-04-IST-01, a coordinated effort of European experts and developers of reflectometry systems, whose main results were: (i) the proof of principle of a new diagnostic concept able to track and monitor the position and shape of the plasma in the initial stage of the discharge, in the start-up phase, and also at the ramp-down phase; and (ii) the improvement of the capabilities of operation in the stationary phase (flattop) to provide an accurate and precise substitute for the positioning magnetic diagnostics in real-time. Important advances have also been achieved in Finite-Difference Time-Domain (FDTD) simulation codes, allowing access to Two-Dimensional (2D) and Three-Dimensional (3D) sophisticated reflectometry simulations; and in the development, manufacturing, and testing of antenna prototypes. An important issue addressed was the synchronisation between different reflectometers with the start of an experimental validation on the Tungsten (W) Environment in Steady-state Tokamak (WEST). We also describe the advances in hardware, leading to a redesigned, assembled and tested prototype of a compact coherent fast frequency sweeping radio frequency (RF) back-end using commercial Monolithic Microwave Integrated Circuits (MMIC), with the integration of Direct Digital Synthesis (DDS) as continuing work. Another result was the conception of an integrated design workflow for the design, evaluation and implementation of microwave diagnostic systems and its application in the assessment of Plasma Position Reflectometers (PPRs) for High Field (HFS) and Low Field (LFS) Sides of the Divertor Test Tokamak (DTT).

Improved fusion yields at the National Ignition Facility via ramped-profile capsule doping

D. S. Clark, M. Hohenberger, A. Pak, S. Hayes, T. Döppner, A. Allen, B. Bachmann, S. H. Baxamusa, J. Biener, R. M. Bionta, et al.

WCLL and HCCP test blanket systems: common technologies and integration in ITER

I. Ricapito, M.Y. Ahn, A. Aiello, B. Bellin, S. Cho, S. D’Amico, M. Fabbri, F. Fantini, E. Garcia, L. Giancarli, et al.

On the Shafranov shift in stellarators

Per Helander, Nikita Nikulsin

As first shown by Shafranov, toroidal plasmas in magnetohydrodynamic equilibrium tend to expand in major radius when the pressure is increased. Here, an average measure of the resulting Shafranov shift is introduced, and its properties are discussed for various classes of stellarator configurations. It is shown to be particularly small in quasihelical and quasi-isodynamic stellarators with a large number of field periods, which are thus relatively robust to variations in the plasma pressure.

Advanced tritium transport modeling and verification, validation, and benchmarking from component level to fuel cycle scale using TMAP8

Pierre-Clément A. Simon, Casey Icenhour, Lin Yang, Lee Kadz, Chaitanya Bhave, Gyanender Singh, Guillaume Giudicelli, Alexander Lindsay, Paul Humrickhouse, Pattrick Calderoni, et al.

Plasma Conductivity from Warm Dense Matter to the Spitzer Limit Using Mean-Force Kinetic Theory

Lucas J. Babati, Nathaniel R. Shaffer, Louis Jose, Scott D. Baalrud

A theoretical model is developed to compute electronic transport coefficients extending from warm and dense to hot and dilute plasma conditions. This kinetic theory-based approach models strong Coulomb correlations by treating interactions using the potential of mean force, electron degeneracy using the Uehling-Uhlenbeck equation, and diffraction by computing cross sections quantum mechanically. The result provides a fast and accurate means to compute electrical conductivity,thermal conductivity and electrothermal coefficients, including contributions from electron-electron interactions. The model enables accurate calculation of materials properties in many warm dense matter systems, including inertial confinement fusion, stellar evolution, and high energy density plasma experiments.

Aluminum wide-range EOS sensitivity in Z-pinch dynamic-hohlraum liner-foam impact and outgoing radiation

Cong Wang, Zi Li, Weijie Li, Xianjue Peng

In a Z-pinch dynamic hohlraum, an aluminum liner collides with a central foam and converts kinetic energy into radiation, and the liner-foam response depends on the aluminum equation of state (EOS). We construct a wide-range aluminum equation-of-state table from density functional theory (DFT) simulations over solid-liquid-plasma regions, denoted DFT-eos. Mixed deterministic-stochastic finite-temperature DFT (mDFT) gives the electron thermal contribution; quantum molecular dynamics (QMD) with classical calibration gives the ion part. We perform one-dimensional cylindrical radiation magnetohydrodynamics (MHD) simulations at a peak current of 50 MA and rise times of 220-300 ns on a single-layer light foam load. Opacity and electrical conductivity are fixed; only the liner Al EOS is changed between DFT-eos and the quotidian EOS (QEOS). Impact time and peak liner kinetic energy change little between the two tables. Larger differences appear in flight-segment density, the contact state at impact, and the time history of outgoing radiation power at the outer interface.

Quantitative validation of SMBI deposition profiles on EAST using experimentally constrained simulations

Yangdi Yu, Tianyang Xia, Jie Zhang, Jia Huang, Huimin Qi, Dazheng Li, Yanlong Li, Xiaoxue He, Xiaowei Mao, Hang Yu, et al.

Quantitative comparison between SMBI fueling simulations and experiments has long been hampered by the poor constraint on the effective source. Here, the particle increment per pulse is extracted experimentally and used to calibrate the simulation source. For EAST shot 71438, the density evolution from microwave reflectometry is analyzed for nine SMBI pulse groups. The SMBI-induced density increase is isolated from the background by comparing the rising and falling phases around each pulse group. Its radial profile peaks in the mid-pedestal region for every pulse group. Volume integration of this increment provides the experimental reference. The simulations use a multi-fluid model in the BOUT++ framework in which two transport operators are recast into conservative flux form, with the particle balance residual reduced to about 2% of the injected amount, and the perpendicular transport coefficients are constructed from the discrete radial flux balance, with the unphysical changes of the initial density and temperature profiles in source-free evolution reduced by an order of magnitude. For three cases sharing the same nominal molecular flux, the simulated deposition peak agrees with the experimental one in the relative pedestal coordinate. The simulated conversion of the injected particles at the end of the injection is slightly lower than the value inferred from the experiment, while the fraction retained at the end of the pulse is higher. The perturbation thus decays more slowly in the simulation, which we attribute to fast loss channels not represented in the model, such as parallel losses to the scrape-off layer. The edge electron temperature stays on the high-temperature plateau of the dissociation and ionization rate coefficients throughout the pulse, and the inward shift of the deposition with edge cooling reported earlier does not occur under the present conditions.

Are $E>B$ regions essential for particle injection in relativistic magnetic reconnection?

Omar French, Fan Guo, Xiaocan Li, Qile Zhang, Yi-Hsin Liu, William Daughton, Hui Li

During relativistic magnetic reconnection, X-points ($E>B$ regions at vanishing guide field) have been proposed to play an essential role in injecting particles into the nonthermal population. Using fully kinetic particle-in-cell simulations at a range of magnetizations $σ\equiv B_0^2/(4πn_0 m_e c^2) = 12$--$800$, we study in detail how the particle energy gains up to the injection threshold $γ_{\rm inj} = σ/4$ are partitioned into work done inside $E>B$ regions (unmagnetized), within one gyration after exit (re-magnetizing), and at all other times (magnetized). The magnetized channel supplies the largest part of the energy gain for $\sim 95\%$ of injected tracers at $σ= 12$ and $\sim 65\%$ at $σ= 800$. Most of the tracers in this magnetized majority never enter an $E>B$ region before injection. We also compare these injection shares with the earlier studies that proposed an essential role for $E>B$ regions. We conclude that $E>B$ regions are neither necessary for injection nor the dominant direct contributors to pre-injection work by injection share in two-dimensional, nonradiative pair-plasma reconnection at vanishing guide field.

Towards Integrated X-Ray Energy Deposition and Ablation Simulations on Flibe Jet Dynamics for the Athena Fusion Pilot Plant Using OpenFOAM

Sophie L. Sharpe, Abinash Manikan, Kirk A. Flippo, Eric Cervi, Simon Woodruff, Lars Pedersen, Gustav Blankenberg

Hardware-in-the-loop validation of an MPC architecture for real-time equilibrium control of tokamak plasmas at RFX-mod2

G. De Tommasi, S. Dubbioso, N. Ferron, F. Fiorenza, D.G. Lui, G. Manduchi, A. Pironti, C. Vitone

Performance of Al₂O₃ hydrogen isotopes permeation barriers deposited on AISI 316L by Pulsed Laser Deposition

A. Iaboni, C. Carati, G.V. Centomani, V. Chierchia, M.E. Gennaro, G. Marra, A. Pontarollo, G.A. Spagnuolo, C. Alberghi, D. Martelli, et al.

The impact of nonlinear Landau damping on cosmic ray streaming and the role of external turbulence

Rouven Lemmerz, Mohamad Shalaby, Ellen Zweibel, Christoph Pfrommer, Timon Thomas

Cosmic rays (CRs) streaming faster than the Alfvén speed generate Alfvén waves that scatter them. The saturated wave amplitude is regulated by a damping mechanism. This damping controls the CR scattering rate and drift velocity, and thus the rate at which CRs transfer momentum and energy to the ambient plasma, which sets the strength of CR feedback. In the ionized interstellar medium, nonlinear Landau damping (NLLD) is commonly invoked as the dominant damping mechanism for Alfvén waves. We test this assumption with fluid-PIC simulations in which thermal ions and electrons are modeled as fluids with optional Landau closures, allowing us to compare otherwise identical runs with and without NLLD. When waves are self-generated by monoenergetic CRs, runs with and without Landau closures are indistinguishable: NLLD is inefficient and the CRs isotropize in the wave frame. Once high-amplitude Alfvén waves mimicking external turbulence are seeded, NLLD curbs wave growth and equalizes forward- and backward-propagating waves. We show that the saturated drift velocity, which falls below the Alfvén speed, can be accurately predicted from the wave spectra alone. If the CR distribution is undersampled, a numerical instability corrupts the largest resonant scales: unphysical, unresolved pitch-angle gradients resonantly generate backward-propagating waves, driving an inverse cascade that should be absent from purely streaming-driven waves. While power-law CR distributions may permit stronger NLLD, our results indicate that NLLD is unlikely to be an intrinsic saturation mechanism of the streaming instability; instead, its effectiveness hinges on the interplay of streaming-generated modes with those of external origin.

Magnetic Reconnection Governs the Entire Lifecycle of Solar Eruptive Magnetic Flux Rope

Xinkai Bian, Chaowei Jiang, Qingjun Liu, Xueshang Feng, Pingbing Zuo, Yi Wang

While magnetic flux ropes (MFRs) are widely accepted to exist prior to many solar eruptions, the physical mechanism responsible for triggering and subsequently driving their eruptions remains debated. Classical models commonly attribute eruption onset to ideal magnetohydrodynamic instabilities, particularly the torus instability, while magnetic reconnection is often regarded as a secondary process. Using high-resolution three-dimensional MHD simulations, we investigate the eruption of an MFR that forms self-consistently through flux cancellation driven by converging motions and photospheric diffusion following an initial shearing phase. The pre-eruption MFR rises quasi-statically and reaches a height where the decay index exceeds the classical torus instability threshold, yet the system continues to evolve quasi-statically without eruption. Instead, eruption begins only when the current sheet beneath the MFR becomes sufficiently thin for magnetic reconnection to set in. Increasing numerical resolution systematically delays the eruption onset, whereas the decay index at eruption onset remains nearly unchanged, demonstrating that the onset is governed by reconnection rather than torus instability. During the eruption, magnetic reconnection continuously converts surrounding sheared arcades into newly reconnected twisted flux that merges with the pre-eruption MFR and continuously to build the erupting MFR. A component-resolved analysis of the Lorentz force work further shows that the newly reconnection flux contributes predominantly to the main acceleration phase. These results demonstrate that magnetic reconnection plays a central role throughout the entire lifecycle of the eruptive MFR: it builds the MFR, directly triggers its eruption, and provides the dominant driving of the eruption.

Flares and flux ropes: an entangled story

Rony Keppens, Yang Guo, Wenzhi Ruan

Solar flares serve as standard candles for all magnetic-reconnection-based energy releases, and their consequences into the heliosphere can be modeled from first principles. This review presents the latest developments in modeling solar flares and their associated flux rope expulsions with state-of-the-art multidimensional magnetohydrodynamic (MHD) descriptions. Observationally established ingredients beyond a single-fluid, thermal plasma evolution have been incorporated to varying degrees, and we highlight self-consistent efforts realized in "standard flare" setups.

Fusion digital twins from imperfect models

Ionuț-Gabriel Farcaș, Frank Jenko

Data-Driven Prediction of Tritium Transport Parameters for Fusion Reactor Fuel Cycle Modeling

Minxiang Shu, Wenxiang Jiang, Shenghan Cheng, Yu Li, Yang Yang, Zhilin Chen

Ion Cyclotron Heating control framework for ITER Plasma Control System: Simplified control-oriented models and preliminary control functions

A. Perez Pecharroman, A.T. Vu, P.C. de Vries, A. Bustos, I.S. Carvalho, W. Helou, F. Kazarian, E. Lerche, M. Schneider