Concept

Stellarator

Related publications (32)

Stellarator divertor design by optimising coils for surfaces with sharp corners

In stellarators, achieving effective divertor configurations is challenging due to the three-dimensional nature of the magnetic fields, which often leads to chaotic field lines and separatrices surrounded by a thick stochastic layer. This work presents a novel approach to directly optimise modular stellarator coils for a sharp X-point divertor topology akin to the Large Helical Device’s (LHD) helical divertor using a target plasma surface with sharp corners. By minimising the normal magnetic field component

2026

ICRH simulations for the Wendelstein 7-X stellarator

We present the current status of ion-cyclotron-resonance heating (ICRH) simulations for Wendelstein 7-X (W7-X), a large, superconducting, optimized stellarator in Greifswald, Germany. More experimental experience with the ICRH antenna at W7-X, in dipole and monopole configuration, has been gained in the experimental campaign conducted from autumn 2024 to spring 2025. Several tools are available for explaining the experimental findings and for planning new experiments. They range from simple cold plasma mode

2026

Impact of divertor closure on power exhaust in Negative Triangularity in TCV

Holger Reimerdes

Negative triangularity (NT) is a promising ELM-free candidate for future fusion reactors. In this paper, the impact of increased divertor closure on density-ramp induced detachment in NT is assessed in the Tokamak `a Configuration Variable (TCV). Previous experiments in TCV have shown that at similar line-averaged density and divertor shape, NT shaping makes detachment access more difficult than in Positive Triangularity (PT) and results in a lower divertor neutral pressure. In this

IOP Publishing2026

Overview of Wendelstein 7-X high-performance operation

The Wendelstein 7-X (W7-X) stellarator has completed two consecutive experimental campaigns OP 2.2 (Sep.-Dec. 2024) and OP 2.3 (Feb.-May 2025) under a new operational strategy enabling more than one year of uninterrupted device availability. This approach, supported by exceptionally high subsystem reliability, allowed sustained high-efficiency plasma operations with up to 80–100 discharges per day across a broad range of magnetic configurations. Several key technical upgrades-most notably the first operatio

IOP Publishing Ltd2026

Boundary turbulence simulations of the optimized HSX stellarator and comparison with experiments

We present the first-ever full-

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, three-dimensional, two-fluid simulation of plasma turbulence based on the drift-reduced Braginskii equations in the optimized HSX stellarator in its quasi-helical configuration. The simulation is carried out by using the \texttt{GBS} code, adapted to simulate 3D magnetic fields with large torsion and ellipticity. The simulation results are compared with edge measurements performed by \textit{Guttenfelder et al.} (2009) using Langmuir probes and Thomson scattering. The com

IOP Publishing Ltd2026

Overview of the MAST Upgrade physics programme: testing novel concepts at low aspect ratio to inform future devices

Olivier Sauter, Holger Reimerdes

The research programme performed on the Mega Amp Spherical Tokamak (MAST) Upgrade experiment has made significant advances in developing the physics understanding of low aspect ratio tokamaks in support of the operation of ITER and design of fusion powerplants. High performance plasma scenarios have been developed to facilitate a broad programme of experiments, in which confinement is constrained by the presence of m/n = 2/1 modes that cause substantial losses of fast ions. The onset of these modes coincide

IOP Publishing Ltd2026

Advances in 3D transient plasma dynamics and control through MHD and hybrid fluid-kinetic simulations with JOREK

Transient phenomena and their control are of high relevance in magnetic confinement fusion plasmas to guarantee a stable and safe plasma operation. Interpretative simulations can maximize the insights gained from experiments on present machines and predictive simulations can help in the preparation of design, mitigation techniques and operational scenarios for future devices. In this article, we provide an overview of recent advances and novel scientific results obtained with the 3D non-linear hybrid fluid-

IOP Publishing Ltd2026

Well-posedness and finite element approximation of the electrostatic shear Alfvén wave equations

Marco Picasso

The aim of this paper is to study the well-posedness and finite element approximation of the electrostatic shear Alfvén wave equations, a coupled system of two partial differential equations arising in plasma physics as a simplified sub-model of the drift-reduced Braginskii equations. To this end, anisotropic Sobolev spaces depending on the normalized magnetic field b are introduced, together with a Poincaré-type inequality along the integral curves of b, which holds under a geometric directedness condition

2026

Spherical Tokamak Physics Research in Preparation for the Operation of Nstx-u

The National Spherical Torus Experiment Upgrade (NSTX-U) is preparing to resume operation, representing a crucial step toward realizing compact, cost-effective fusion pilot plants. In advance of this, extensive modeling and data analysis have been conducted to advance the physics basis for low-aspect-ratio, high-performance plasma regimes, focusing on three core objectives: confinement and stability, power and particle handling, and steady-state operation. Significant progress has been made in understanding

IOP Publishing Ltd2026

Progress and innovations in the TCV tokamak research programme

Olivier Sauter, Ambrogio Fasoli, Stefano Coda, Basil Duval, Yves Martin, Laurent Villard, Stefano Alberti, Ivo Furno, Patrick Blanchard, Jean-Philippe Hogge, Holger Reimerdes, Stephan Brunner

Research on the Tokamak à Configuration Variable (TCV) addresses a wide range of key questions relevant to ITER and future fusion power plants. Over the past two years, highly productive experimental campaigns have led to major advances across several areas: the ITER baseline scenario; pedestal properties in low-collisionality, peeling-limited conditions; and the development of high-

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, non-inductive regimes. Alternative high-confinement scenarios have likewise received significant attention, with re

IOP Publishing2026

Initial observations in X-point target divertor discharges on MAST-U

The first high-power (≥ 3 MW) H-mode experiments using a double-null X-point-target (XPT) divertor configuration have been performed on MAST-U. The XPT geometry is obtained by combining a large strike point radius, similar to the Super-X divertor (SXD), with an additional X-point near the separatrix in the baffled outer divertor chambers and leads to additional exhaust benefits over the SXD. The broader electron density profile near the secondary X-point leads to additional plasma-neutral interactions, evid

IOP Publishing2026

Investigating long-duration plasma operation with the international multi-machine CICLOP database

Stefano Coda

Combined high-fusion performance and long-pulse operation is one of the key integration challenges for fusion energy development in magnetic devices. Addressing these challenges requires an integrated vision of physics and engineering aspects with the purpose of simultaneously increasing time duration and fusion performance. Since the previous 2023 IAEA Fusion Energy Conference, significant progresses have been made in tokamaks and stellarators including very recent achievement in duration and/or performanc

IOP Publishing Ltd2026

Design, Installation, and First Results from the Ion Cyclotron Emission Diagnostic on TCV

Basil Duval

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

2026

Poloidal field coils optimization for the MANTA tokamak using TokaMaker

Utilizing the TokaMaker code, this manuscript presents a scheme for determining the optimal locations of poloidal field coils in tokamak configurations, aimed at reducing the currents required to reproduce target equilibrium in future devices. The definition of the coil position space is described, as well as the cost function is to be minimized, which incorporates the constraints of the problem. The MANTA reactor design, featuring strong negative triangularity shaping, is considered as a test example, wher

AIP Publishing2026

Impact of triangularity on power sharing and boundary turbulence in TCV double-null L-mode plasmas

Stefano Coda

We present a systematic experimental study of triangularity effects on power sharing, Scrape-Off Layer (SOL) transport, and boundary turbulence in Double-Null (DN) L-mode plasmas in TCV. We show that triangularity (δ) strongly influences inner/outer power sharing between divertor targets. In high-δ DN plasmas (δ = 0.58), only 13% of the exhaust power reaches the inner targets, while in low-δ DN (δ = 0.17) this fraction rises to 28%. In Lower Single-Null plasmas, the inner target power fraction increases fro

IOP Publishing2026

Non-inductive high-performance discharges on TCV on the path to steady state

Olivier Sauter, Stefano Coda

An extended experimental effort is underway on the TCV tokamak to develop scenarios compatible with long-pulse operation, featuring mostly non-inductively driven current – preferably with a large fraction of bootstrap current. A closely related goal is to achieve good plasma performance, typically measured through the normalized beta beta_N. This work is part of a broader endeavor involving several European tokamaks, under the auspices of the Tokamak Exploitation Work Package (WPTE) of EUROfusion, and aimed

IOP Publishing2026

Data-driven Model Order Reduction for Accelerating Boundary Plasma Turbulence Simulations

Simone Deparis

Machine learning (ML)-driven reduced-order modelling is applied to accelerate steady-state convergence in three-dimensional, nonlinear, flux-driven two-fluid simulations of boundary plasma turbulence. A parametric scan of plasma resistivity, heating and density sources is performed to generate comprehensive datasets across various turbulent regimes for model training and validation. To efficiently manage and interpret these datasets, we apply the proper orthogonal decomposition technique to reduce the dimen

CAMBRIDGE UNIV PRESS2026

Suprathermal electron transport studies in radio-frequency-heated tokamak plasmas

Stefano Coda

This contribution reports on the study of suprathermal electron radial transport enhancement in the presence of electron-heating radio-frequency waves, such as electron-cyclotron waves or lower-hybrid waves. Since suprathermal electrons emit hard X-rays from Bremsstrahlung, experimental data from hard X-ray measurements are used to follow their dynamics. In particular, electron-cyclotron power modulation experiments performed in TCV show that this transport depends on the total electron-cyclotron power. The

EDP Sciences2026

First benchmark between the KINetic Deterministic NEutral Solver (KINDNES) and EIRENE

Holger Reimerdes

This work presents the KINetic Deterministic NEutral Solver (KINDNES) and its first benchmark with EIRENE (Reiter et al., 2005). Neutral particle dynamics are crucial for fluid and gyrokinetic edge plasma simulations in magnetically confined devices. While most existing neutral models fall into either deterministic fluid approximations or Monte Carlo kinetic models, KINDNES offers the advantages of a kinetic model without the drawback of the statistical error inherent to Monte Carlo codes. KINDNES, original

2026

Overview of the ASDEX Upgrade results

Olivier Sauter, Stefano Coda, Basil Duval, Timothy Goodman

After a 26-month vent ASDEX Upgrade (AUG) went back in operation with a newly designed upper W-divertor suitable for alternative divertor configurations (featuring in-vessel coils and cryo-pump). Parameter scans and an extensive set of measurements were obtained and their interpretation is ongoing. Prompted by the ITER wall change, dedicated experiments on non-boronized plasma startup were contrasted to that employing asymmetric and more symmetric boronizations. The asymmetric boronization proved to be as b

IOP Publishing Ltd2026

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Related publications (32)

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IOP Publishing Ltd2026

\beta_N

, non-inductive regimes. Alternative high-confinement scenarios have likewise received significant attention, with re

IOP Publishing2026