Energetic Particle-Driven Modes and Spontaneous Frequency Sweeping

2025-01-28

Confinement and Stability of Fast Ions in Fusion Plasmas

2025-01-28

This book explores the physics of fast ions and fast ion- driven instabilities. It also describes modern theory of near- critical nonlinear wave– particle systems with the particle source and wave damping. Such a theory was developed by H.L. Berk and B.N. Breizman in the mid- 1990s, and it delivered outstanding results successfully explaining the experimentally observed collective phenomena driven by energetic ions. A systematic and step-by-step analysis of resonant interactions between the waves in plasmas and various types of energetic ion populations is presented and analyzed, taking the readers on an exciting journey into the world of nonlinear physics and cutting-edge experiments performed on the world’s major magnetic fusion machines. The phenomena described in this book will be of interest for researchers studying fusion, solar plasma, space plasma, and for a broader realm of scientists working in nonlinear phenomena. Key Features: Features experimental data and the Berk-Breizman theory on nonlinear evolution of energetic particle-driven waves Describes in simple terms, the recent advances in the diagnostics of energetic particles and Alfvén waves Presents a systematic overview of extrapolating results presented in other types of plasmas (e.g., solar and space) and nonlinear systems.

Analysis of Energetic Particle Driven Modes and Interchange Modes in LHD Plasma Using the Gyro-Fluid Code FAR3d

Journal of Fusion Energy · 2025-11-22

Multiple Modes and Global Transport of Energetic Particles

2025-01-28

Radiative damping of toroidal Alfvén eigenmode in low-shear plasmas

Fundamental Plasma Physics · 2025-02-02 · 2 citations

Instabilities of Alfvén eigenmodes (AEs) are of significant concern because they can enhance the cross-field transport of fusion-born alpha particles beyond the neoclassical level in magnetic fusion plasmas. The threshold value of alpha-particle pressure for exciting AEs depends critically on the damping rate of AEs. The damping mechanisms include kinetic damping due to interactions with thermal particles, continuum damping due to AE frequency crossing Alfvén continuum, and radiative damping due to emitting kinetic Alfvén waves (KAWs). The radiative damping is substantial and can even prevail in high-temperature burning plasmas [1]. We revisit the radiative damping analytic theory for TAE in plasmas with low positive magnetic shear, considering TAE with an eigenfrequency near the bottom of TAE-gap and with poloidal harmonics of the same sign (even TAE). In contrast to earlier papers, we provide the damping calculations in real space rather than Fourier space. This approach is straightforward technically and more enlightening from a physics standpoint for benchmarking numerical calculations of radiative damping. The parametric dependence of the resulting damping rate agrees with that of Refs. [2-5], but it has a smaller numerical factor in front of it.

New interpretation of ion cyclotron emission from a tokamak

Physics of Plasmas · 2025-10-01

The tempting interpretation of ion cyclotron emission in terms of compressional Alfvén eigenmodes involving energetic ions is inconsistent with recent TCV experimental observations in some important aspects, such as (i) the perturbed poloidal field is exceeding the parallel perturbed magnetic field significantly, and (ii) the modes are near cyclotron harmonic and exhibit Alfvèn scaling of their frequency. We show that these characteristics can be explained by considering finite Larmor radius effects of thermal ions in shear Alfvén waves that allow such waves to exist well above the ion cyclotron frequency in the form of wave-packets bouncing within the plasma volume.

Energetic particle physics: Chapter 7 of the special issue: on the path to tokamak burning plasma operation

Nuclear Fusion · 2025-03-24 · 31 citations

Abstract We review the physics of energetic particles (EPs) in magnetically confined burning fusion plasmas with focus on advances since the last update of the ITER Physics Basis (Fasoli et al 2007 Nucl. Fusion 47 S264). Topics include basic EP physics, EP generation, diagnostics of EPs and instabilities, the interaction of EPs and thermal plasma instabilities, EP-driven instabilities, energetic particle modes (EPMs), and turbulence, linear and nonlinear stability and simulation of EP-driven instabilities and EPMs, 3D effects, scenario optimization strategies based on EP phase-space control, EPs in reduced field scenarios in ITER before DT, and the physics of runaway electrons. We describe the simulation and modeling of EPs in fusion plasmas, including instability drive and damping as well as EP transport, with a range of approaches from first-principles to reduced models, including gyrokinetic simulations, kinetic-MHD models, gyrofluid models, reduced models, and semi-analytical approaches.

Reduced model describing resonance overlap threshold for fast ion transport by toroidal Alfvén eigenmodes

Nuclear Fusion · 2025-12-08

Abstract This work introduces a reduced model to predict the ‘resonance overlap threshold’ governing transport of fast ions (FIs) by toroidal Alfvén eigenmodes (TAEs) in tokamak plasmas. TAE-FI resonance occurs within distinct ‘resonance regions’ of particle phase space, which grow wider when the TAE mode amplitude increases. If these resonance regions are separate then FI transport is limited and localised; if multiple resonance regions overlap then large-scale stochastic transport of FIs can occur, jeopardising confinement. Predicting the resonance overlap threshold between these two scenarios is an important problem in the field of FI transport modelling. Current workflows rely on computationally expensive orbit-following codes; the new reduced resonance overlap model provides a much simpler and faster alternative, for ease of implementation in integrated models. In this paper, we apply this approach to passing particles and find good agreement with more detailed numerical modelling, including HALO code simulations. Models based on this approach could provide a useful step in increasing efficiency of predictive modelling for next-generation fusion reactors.

Alfvén Cascade Modes in Reversed Magnetic Shear Equilibria

2025-01-28

Runaway electron-induced plasma facing component damagein tokamaks

Plasma Physics and Controlled Fusion · 2025-11-06 · 8 citations

Abstract This Roadmap article addresses the critical and multifaceted challenge of plasma facing
component (PFC) damage caused by runaway electrons (REs) in tokamaks, a phenomenon
that poses a significant threat to the viability and longevity of future fusion reactors such as ITER
and DEMO. The dramatically increased RE production expected in future high-current tokamaks
makes it very difficult to avoid or mitigate REs in such devices when a plasma discharge terminates
abnormally. Preventing damage from the intense localised heat loads they can cause requires a
holistic approach that considers plasma, REs and PFC damage. Despite decades of progress in
understanding the physics of REs and the thermomechanical response of PFCs separately, their
complex interplay remains poorly understood. This document aims to initiate a coordinated,
interdisciplinary approach to bridge this gap by reviewing experimental evidence, advancing
diagnostic capabilities, and improving modelling tools across different scales, dimensionalities,
and fidelities. Key topics include RE beam formation and transport, damage mechanisms in
both brittle and metallic PFCs, and observed effects in major facilities such as JET, DIII-D,
WEST and EAST. The Roadmap emphasises the urgency of predictive, high-fidelity modelling
validated against well-diagnosed controlled experiments, particularly in the light of recent changes
in ITER’s wall material strategy and the growing importance of private sector fusion initiatives.
Each section of the Roadmap article is written to provide a concise overview of one area of
this multidisciplinary subject, with an assessment of the status, a look at current and future
challenges, and a brief summary. The ultimate goal of this initiative is to guide future mitigation
strategies and design resilient components that can withstand the intense localised loads imposed
by REs, thus ensuring the safe and sustainable operation of the next generation of fusion power
plants.