The existence of electromagnetic cylindrical modes is demonstrated in advanced tokamak scenarios with reversed magnetic shear. Unlike the pressure driven reverse shear Alfven eigenmode and ballooning/infernal mode, it is found that the triggering of such modes demands two essential conditions: a nonmonotonic safety factor and the kinetic compression effect of thermal particles. Accordingly,...
Recent deuterium-tritium (D-T) experiments at JET have uncovered a range of new phenomena involving alpha-particles and energetic ions in the plasma [1-3]. Understanding and controlling alpha particles is an important task for ITER, given its goal to achieve Q = 10 in plasmas with a full-tungsten first wall and divertor. Key challenges include developing diagnostics to measure alpha particles...
The advent of artificial intelligence [AI] has a deep impact on numerous scientific and industrial fields, particularly in magnetic confinement fusion. This work explores the application of AI techniques to help scientists with the design of future fusion experiments based on previous experimental campaigns. Traditional ways of interpreting and designing fusion discharges often require...
The operation of spherical tokamak ST-40 (a =0.27 m; R =0.5 m; b/a =1.4 – 2.0) with high toroidal magnetic fields of up to 2.2 T, plasma currents up to 750 kA, and plasma heating by neutral beam injection (NBI) has exhibited a variety of Alfvén eigenmodes (AEs) excited by the NBI-produced energetic ions. In these experiments, two NBI sources were employed, with the beam energy up to 55...
In magnetic confinement fusion plasmas, the confinement performance of α particles is crucial for maintaining steady-state burning plasma. Under classical conditions, α particles heat the bulk plasma through Coulomb collisions, and even considering the toroidal magnetic field structure of tokamaks, the neoclassical transport levels remain low. However, the kinetic effects and...
Identifying energetic particle driven modes in spectrograms is crucial in generating large databases. These databases are essential for advancing physics research and training machine learning models for real time control. However, to train supervised machine learning algorithms, large databases labelled by humans must be used, which is practically impossible taking into account the amount and...
ITER will be among the first experiments with extensive number of fusion-born alpha particles. The research plan of ITER includes studying this burning plasma physics domain. However, to learn from these experiments, a necessary requirement is to be able to measure these fusion-born alphas. To this end, ITER is limited to measure confined distributions using gamma-ray spectroscopy and...
Orbital dynamics of fusion-born alpha particles in Z-pinch geometry are analyzed using magnetic trapping conditions specialized to self-magnetic fields. A magnetic trapping parameter, defined as the ratio of potential-to-kinetic components of canonical momentum, emerges as the key parameter governing orbit characteristics. The analysis reveals a fundamental asymmetry in alpha particle...
In this work we report on the implementation and verification of a phase-space resolved energetic particle (EP) transport model [1, 2]. It is based on the Phase Space Zonal Structure transport theory [3, 4, 5] , which extends the conventional transport equations into Phase Space and consistently evolves a (nonlinear) equilibrium referred to as the Zonal State. Its focus is primarily directed...
Quasilinear simulations can be an effective reduced tool for predicting and interpreting fast ion transport in fusion devices. At the core of these transport models is the form of their diffusion coefficients (or resonance functions), which have a leading role in determining the resonant wave saturation levels. While conventional quasilinear theory requires a random phase approximation to be...
Abstract: A workflow is developed[1] based on the ideal MHD equations to investigate the linear physics of various Alfvén eigenmodes in general axisymmetric toroidal geometry by solving the coupled shear Alfvén wave (SAW) and ion sound wave (ISW) equations[2,3] in ballooning space. The model equations are solved by FALCON code[4] in the singular layer, and the corresponding solutions are then...
The recently upgraded Fast Ion Loss Detector (FILD) installed on the TCV tokamak can simultaneously measure co- and counter-current fast-ion (FI) losses with high-temporal (1 microsecond) and high-spatial resolutions. This allows, for the first time, resolving sub-millisecond changes in the velocity-space of the FI losses. These new capabilities have been extensively used to characterise the...
Shear Alfvén waves destabilized by neutral beam injection are quite common in TJ-II plasmas [1] and provide a good testing ground for model validation purposes in non-axisymmetric configurations. In order to obtain a set of well-characterized Alfvén perturbations, we have carried out a series of experiments on plasmas with combined ECRH and NBI heating using different magnetic configurations....
In this study, a comprehensive gyrokinetic analysis was performed to investigate the effects of fast ions on turbulence in KSTAR FIRE (Fast Ion Regulated Enhancement) mode plasmas, having high performance due to an internal transport barrier correlated with a substantial fast ion fraction (≳0.4 at r/a<0.47, where a is a minor radius) [1]. The analysis focused on the fast ion effects on...
The Spherical Tokamak for Energy Production (STEP) programme is focused on designing and building a prototype fusion power plant that will generate approximately 1.5-1.8 GW of deuterium-tritium fusion power. To achieve this, the alpha-particles generated through fusion must be confined sufficiently to maintain thermonuclear bulk ion temperatures in the plasma core and to protect the wall from...
MeV-range Neutral Beams (NBs) in ITER plasmas are essential for heating and sustaining plasma scenarios through, e.g., current-drive and torque injection. However, NB injection into low-density plasmas can result in inefficient beam ionisation and localised high-energy neutral particle losses on the Plasma-Facing Components (PFCs). This well-known phenomenon, shine-through, poses a significant...
The study of fast-ion transport, driven by auxiliary heating methods such as neutral beam injection (NBI) and/or ion cyclotron range of frequencies (ICRF) waves, is critical for optimizing plasma performance and advancing fusion reactor development. Neutron diagnostics, particularly neutron spectroscopy, play a pivotal role in analyzing neutron emissions to investigate fast ions. Neutron...
We present a simple theoretical study of the fast ion effect on the ExB staircase in a magnetized plasma, extending previous works by Lilley-Nyqvist14 and Garbet21. In this study, the ExB staircase is a self-generated radially periodic ExB flow structure described by the wave kinetic equation and the modified Hasegawa-Mima equation, with the trappings of drift wave packets by the periodic...
Future nuclear fusion reactors will be heated by neutral beam injectors (NBI) and high frequency electromagnetic waves as well as fusion born alpha particles. Consequently, a reactor relevant plasma hosts multiple energetic particle (EP) populations that will interact non-linearly between them and the thermal plasma, affecting the system stability and leading to potential harmful effects on...
Instabilities such as Edge Localised Modes (ELMs) can degrade confinement in tokamak plasmas, potentially leading to damaging heat fluxes on the first wall [1, 2]. Externally applied Magnetic Perturbations (MPs) are used to mitigate, and even suppress these instabilities [3]. This suppression technique is under investigation in many tokamaks, and its understanding is crucial for future fusion...
Energetic particle (EP) physics is one of the key issues in magnetic confinement fusion research, and fishbone instability, as an important branch of EP physics, plays an important role in plasma confinement and transport. Fishbone cycle frequency (ffc) refers to the reciprocal of the time interval between neighboring fishbones, and the larger the cycle frequency, the denser the fishbones. It...
Electromagnetic modes driven by pressure gradient in the core plasma can not only restrict plasma confinement, but also cause energetic particle loss. The kind of instability has become a major concern in the present and future fusion devices, especially for which operate with reactor-relevant parameters. To reveal underlying effects of electron cyclotron resonance heating (ECRH) on...
Employing both nonlinear gyrokinetic simulation and analytical theory, we have investigated the effects of zonal (electromagnetic) fields on the energetic particle's drive of reversed shear Alfv´en eigenmodes in tokamak plasmas. Contrary to the conventional expectation, simulations with zonal fields turned on and off in the energetic particle dynamics while keeping the full nonlinear dynamics...
Toroidal Alfvén Eigenmodes (TAEs) [1] are of significant interest in tokamak research because they can transport energetic particles and interact with turbulence. While the former poses a challenge for sustaining plasma confinement in devices like ITER and future fusion reactors [2], experimental evidence [3] suggests the latter effect could enhance plasma confinement.
We present simulations...
Instabilities measured in the Large Helical Device (LHD) are studied for the presence of Alfven eigenmodes and their effects on the fast-ion distribution. LHD is equipped with an array of magnetic probes that measure fluctuations in the toroidal component of the B-field up to 500 kHz. Magnetohydrodynamic instabilities have been measured at various frequencies ranging from 50 kHz up to 350 kHz....
Energetic particle driven instabilities and redistribution in phase space in a tokamak burning plasma with reversed magnetic shear are investigated with kinetic-magnetohydrodynamics (MHD) hybrid simulations. The initial equilibrium is based on an ITER steady-state scenario with 9 MA plasma current and was studied for energetic particle driven instabilities in a previous work [1]. In addition...
Recent upgrades of the heating systems and new diagnostic capabilities have expanded the capabilities of the Tokamak à Configuration Variable (TCV) to address energetic particle (EP) physics. A second Neutral Beam (NB) injecting at Vinj~53kV complements the first system with maximum Vinj~28kV [1], with a total NB power of 2.8MW now available to study EP dynamic and the interaction with...
Energetic alpha particles generated as by-product of D-T fusion reactions may give rise to plasma instabilities such as Alfvén eigenmodes (AEs) 2, which can de-confine alphas, leading to inefficient plasma self-heating and erosion of the wall-components. Analyzing the impact of energetic alpha particle transport in such reactor level fusion devices is of crucial importance for optimizing the...
Spatial channeling – the fast-ion energy and momentum transfer across the magnetic field by destabilized modes – affects plasma performance, deteriorating or improving it [1-3]. It manifests itself, in particular, by twisting the mode radial structure, which was observed in experiments on tokamaks, see [4,5] and references therein. In this work, it is revealed that there is a correlation...
An exhaustive understanding of the mechanisms behind energetic-particle (EP) transport and loss-es is of vital importance for the development of future fusion machines [1], as these particles are a key source of energy and momentum. Furthermore, when localized, energetic-particle losses can damage plasma-facing components [2]. The development of new diagnostic and analysis tech-niques is...
Evidence from DIII-D experiments demonstrates that ion temperature gradient (ITG) turbulence can significantly decrease in response to Alfvén eigenmode (AE) activity in neutral-beam-heated discharges. This phenomenon is consistently observed across multiple discharges. Local ITG turbulence is reduced by ~50% in cases with a single toroidal AE (see the Fig. 1) and, in some instances, is...
Recent experiments at the DIII-D tokamak in the ongoing Energetic Particle (EP) Turbulence thrust have acquired data documenting the impact of varied effective pitch-angle scattering rate (νeff) on the saturation level of fast-ion-driven instabilities. These experiments, focused on the current ramp, aimed to change microturbulence induced pitch-angle scattering in the presence of a single...
Due to their relatively higher Vbeam/VAlvén ratio, spherical tokamaks like MAST-U are ideal to investigate high-frequency beam-ion driven modes such as Compressional Alfvén Eigenmodes (CAEs) and Global Alfvén Eigenmodes (GAEs) [1, 2]. Besides, the scintillator-based Fast-Ion Loss Detector (FILD) [3] in MAST-U, provides enough sampling frequency to detect fast-ion losses induced by such...
The relationship between the excitation of reversed shear Alfv\'en eigenmodes (RSAEs) and the formation of internal transport barrier (ITB) have been investigated in the EAST tokamak. A series of discharge conditions with the minimum safety factor, $q_{min} \approx 2$, have been established through the synergy effect of lower hybrid current drive (LHCD) and electron cyclotron resonance heating...
The SPARC tokamak is now under construction in Devens, Massachusetts, USA, and its highest performing “Primary Reference Discharge” (PRD) is expecting >10 MW of ICRF heating power, >20 MW of alpha power, and >100 MW of DT fusion power [Creely JPP 2020]. Fast ion (FI) driven MHD instabilities, specifically Toroidal Alfven Eigenmodes (TAEs), have been investigated for the PRD with a variety of...
The SPARC tokamak, under construction in Devens, Massachusetts, USA, plans to begin operation in 2026 and is predicted to produce over 100 MW of DT fusion power in a high power H-mode [Creely JPP 2020]. The results from this device will inform the design of ARC, a fusion power plant which aims to begin operation in the early 2030s. This work will show simulation results from the Monte Carlo...
The fast-ion deuterium Balmer-alpha (FIDA) spectroscopy diagnostic has been operated on KSTAR tokamak. KSTAR FIDA diagnostic system consists of two tangential viewing arrays covering both blue-shifted and red-shifted fast-ion charge-exchange spectra. Since the tangential viewing FIDA is sensitive to the emission from the passing fast-ions, primarily generated by the tangential NBI on KSTAR,...
Fast-ion driven Alfvén Eigenmodes (AEs) are observed during ICRF heated high-βp plasmas on EAST since AEs quiescence was discussed in [1]. Multiple high frequency modes are observed for shot 112670 at fTAE1 ~ 145 kHz, n = 3, δB/B ~ 4× 10-4 and fTAE2 ~ 175 kHz, n = 4, δB/B ~ 1.2×10-5 measured by high-frequency mirnov coil, at B0 ~ 2.45T, Ip ~ 350kA , n ~ ramp-up from 3.5× 1019m-3 to ~ 4×...
The impact of resonant magnetic perturbation (RMP) on the loss of energetic passing ions is investigated through numerical simulations. It is found that the poloidal components of the RMP field, with poloidal mode numbers significantly higher than those of particle orbits, exert a non-negligible influence on the drift islands of energetic particles (EP), as shown in Fig.1 of the attached pdf...
The Divertor Tokamak Test (DTT) facility [1] is a compact, high-field tokamak being designed and constructed with the primary goal of studying heat exhaust in conditions similar to those of ITER and DEMO in steady-state. Up to 10 MW of negative-ion based neutral beam injection (NBI) with an injection energy of 510 keV, and 6 MW of ion cyclotron resonance heating (ICRH) are currently being...
Understanding and mitigating MHD instabilities driven by energetic particles is critical for advancing tokamak performance in future fusion reactors. JT-60SA provides a unique platform for exploring these phenomena under DEMO-relevant conditions, leveraging its 500 keV super-Alfvénic Negative Neutral Beam Injection (N-NBI) for off-axis current drive and heating. The fast-ion loss detector...
Understanding the mechanisms responsible for fast ion losses is critical for the success of future magnetically confined fusion power plants. Towards this goal, a double pinhole collimator has been developed for a fast ion loss detector (FILD) [1] in the ASDEX Upgrade tokamak. This collimator features a mirrored design of the FILD geometry. FILDSIM [2] simulations were applied to optimize the...
Recurrent bursting Alfvénic instabilities, accompanied by a rapid and violent release of stored free energy, are deleterious to the plasma confinement and threaten vacuum vessel integrity. Unlike beam-driven Alfvén eigenmodes (AEs), which often exhibit bursting behavior [1], AEs during ion cyclotron resonance frequency (ICRF) heating typically maintain steady amplitudes [2,3], despite...
Confinement of energetic particles (EP) is crucial to ensure the transfer of energy to the thermal plasma and to achieve self-sustained fusion reactions. Together with EP, turbulence is another major element in the description of a fusion plasma. When both EP and turbulence co-exist, their mutual interplay cannot be neglected. Whereas the impact of EP on turbulence has extensively been...
We extend the MHD spectroscopy framework proposed earlier [1] to incorporate new effects arising from the modification of the geodesic acoustic mode (GAM) frequency by the anisotropic energetic particles (EP) pressure in the presence of the magnetic field reversed shear. These enhancements offer dual advantages: improving the accuracy of $q_{min}$ reconstruction and enabling the inference of...
Gamma-rays generated in nuclear reactions were used in JET for decades to study the main mechanisms of fast-ions slowing down, redistribution and losses for development optimal plasma scenarios with auxiliary plasma heating [1]. The recent JET deuterium-tritium experiments (DTE) verified the feasibility of the confined α-particle diagnosing and monitoring D-T fusion rate. Also, a novel...
Recent work [1] has investigated the effect of a magnetic island chain modification on the shear Alfvén continuum for a large aspect tokamak using ideal MHD theory. By creating new flux based magnetic island coordinates, it was shown that the magnetic island chain reduces the width of the TAE gap in the shear Alfvén continuum.
This raises the possibility that a TAE, originally experiencing...
Alfven eigenmodes (AE) driven by energetic particles (EP) can cause large EP transport that degrades plasma confinement and threaten machine integrity. Understanding the nonlinearly saturated AE amplitude and associated EP transport level is needed for extrapolating EP confinement properties to burning plasma experiments such as ITER.
Global gyrokinetic simulations find strong zonal...
M. Fitzgerald1, B.N. Breizman2
1 United Kingdom Atomic Energy Authority, Culham Campus, Culham Science Centre, Abingdon, Oxon, OX14 3DB, UK
2 Institute for Fusion Studies, The University of Texas, Austin, TX 78712, United States of America
Compressional Alfven eigenmodes (CAEs) and global Alfven eigenmodes (GAEs) with frequencies comparable to the ion cyclotron frequency have been...
δf gyrokinetic codes often hardcode the Maxwellian distribution as the equilibrium distribution for all species involved in the simulations, mainly because of the difficulties in handling the polarization density for distributions other than Maxwellian. Alpha particles often take the slowing-down distribution, which usually significantly deviates from the Maxwellian one.
For some...
In the ITER hybrid scenario, which is characterized by a centrally flat safety factor profile slightly above unity ($q > 1$), a bifurcated 3-D MHD equilibrium with a tilted magnetic axis—known as a helical core (HC)[1-4]—can form due to the ideal saturation of kink[2]/quasi-interchange[5] modes. Prior HC formation studies in ITER using VMEC[6], a 3-D equilibrium solver, have shown that the...
Excitation of high-frequency modes via resonant interaction with fusion-born α-particles is one of the most important problems for burning deuterium-tritium (DT) plasma operation, such as ITER [1]. During DTE2 campaign on JET, a novel scenario was found of exciting high-frequency modes by α-particles aiming at establishing a bump-on-tail (BOT) distribution. JET baseline discharges with q(0)~1...
Abstract. The effect of highly energetic particles (EPs) needs to be well understood in future burning plasma experiments as they will provide a large fraction of the total pressure and can strongly interact with the thermal bulk plasma. In this contribution we describe numerical simulations of n=1 instabilities in tokamak plasmas like the internal kink and fishbone mode which is driven...
As the magnetic confinement fusion community prepares for the next generation of fusion devices and burning plasmas, there is still a question of whether fast ions (FIs) will drive MHD instabilities, causing significant redistribution or even loss of FIs, thereby leading to reduced plasma performance and possibly threatening the integrity of the first wall. In this paper, we explore the...
The Ion Cyclotron Emission (ICE) driven by NBI, ICRH, and fusion reactions was observed in many toroidal fusion devices and is well studied theoretically. Much less attention has been paid to the ICE in the tokamak Ohmic discharges. Although this ICE was first observed as long ago as in the 80’s [1], at present there is no clear understanding why it arises despite the absence of fast ion...
The edge velocity-space distribution of the fast ions can play a significant role in the access of some high-confinement modes via an additional plasma rotation or by possible mutual interaction with the edge MHD modes. In addition to their charge-exchange (CX) collisions with main neutral atoms D, edge fast ions collide with working-gas molecules D2. The reactions produce fast neutrals which...
Accurately characterizing fast-ion distributions in fusion plasmas is crucial for understanding and controlling alpha heating and instabilities in future reactors. This work presents a significant advancement in fast-ion tomography by introducing a novel technique that not only reconstructs fast-ion distributions but also identifies the specific transport mechanisms responsible for shaping...
The ITER measurement requirements call for diagnosing energy spectra and densities of fusion-born alpha-particles and other energetic particles. This can be accomplished by velocity- or phase-space tomography based on several simultaneously acquired measurements using diagnostics with high spectral resolution, such as gamma-ray spectroscopy (GRS), neutron emission spectroscopy (NES) and...
In this work, we analytically investigate energetic particle-driven geodesic acoustic modes (EGAMs) by considering non-circular cross-sections of tokamaks. In the framework of the gyro-kinetic equation, we find that shaping effects can introduce additional energetic particle-wave resonance points at $\omega = n \omega_t^h \left( n = 2, 3, 4 \right)$, where $\omega$ and $\omega_t^h$ are EGAM...
Alpha particle confinement is crucial for sustaining burning plasmas and designing future reactor concepts. Along with classical/prompt losses, various MHD instabilities can lead to wave-particle interactions which can transport alpha particles outward from the plasma. This can result in a reduction in plasma heating/performance, and, at worst, damage in-vessel components. JET's recent DT...
Negative triangularity (NT) shaped plasmas emerge as an attractive scenario with high fusion performance and power handling capabilities. Recent experiments at the TCV and DIII-D tokamaks have demonstrated fusion-relevant ELM-free H-mode like confinement levels. While NT shaped plasmas have shown little to no effect on fast-ions in DIII-D [1], a mitigation of fast-ion driven Toroidally induced...
This contribution explores the detailed drive of Alfvén eigenmode activity in dedicated KSTAR energetic particle experiments. The broad purpose of these experiments has been to develop scenarios to study energetic particle driven modes, as well as enable experimental studies of wave-particle-plasma interaction and particle loss at higher beam power. To date, the authors have reported the drive...
The ARC fusion power plant is a high-field tokamak design, with underlying principles being demonstrated by the SPARC tokamak. These projects are spearheaded by Commonwealth Fusion Systems (CFS) in Devens, MA, USA. SPARC and ARC are projected to achieve fusion gains of Q ≃ 10 [1] and Q ≃ 50 [2], respectively. At these gains, a burning plasma regime is realized where DT-fusion alpha particles...
Ion cyclotron emission (ICE) driven by fast ions is an electromagnetic radiation whose spectrum peaks correspond to the harmonics of the cyclotron frequencies of energetic ion species near the emission location. ICE carries numerous fast ions and substantial distribution information, and their detection and analysis can help understand the behavior of fast ions in a magnetically confined...
Measurements of beam driven Alfvén Eigenmode (AE) activity in matched deuterium (D) and hydrogen (H) DIII-D plasmas are found to exhibit a dramatic difference in unstable mode activity and fast ion transport for a given injected beam power[1]. The dependence of the unstable AE spectrum in reversed magnetic shear plasmas on beam and thermal species is investigated in the current ramp by varying...
This work presents simulations of alpha-particle transport due to static 3D magnetic field perturbations in ITER, specifically those arising from Toroidal Field (TF) Ripple, ferromagnetic materials, and Resonant Magnetic Perturbations (RMPs) arising from edge-localized mode (ELM)-control coils, which have been reported to significantly increase losses in existing devices [1].
We employ the...
We tackle a critical challenge in simulating $MeV$-range fusion products, such as $\alpha$-particles and auxiliary heating beam ions: accurately modeling their relatively long slowing down in the presence of Alfvén eigenmode (AE) instabilities, including toroidicity-induced Alfvén eigenmodes (TAEs) and reversed shear Alfvén eigenmodes (RSAEs). Fusion reactors like ITER are expected to rely on...
Ion cyclotron resonance heating (ICRH) is an important auxiliary heating method in tokamak devices. It also produces a large number of energetic particles (EPs) with energies up to MeV, which can potentially destabilize variety of instabilities such as Alfvén eigenmodes (AEs) or fishbone. Recently, several modes with frequencies ranging from $50$ to $300 kHz$ have been observed in high...
Neoclassical ambipolar radial electric field Er could suppress the microturbulence to improve confinement in stellarators. It can also affect energetic particle transport and be modified by energetic particle neoclassical loss, which induces a radial current that changes the Er in the stellarators. The intrinsic 3D magnetic field in the stellarators provides a unique possibility of...
We report the first experimental detection of a zero-frequency fluctuation that is pumped by an Alfvén mode in a magnetically confined plasma. Core-localized toroidal Alfvén eigenmodes (TAEs) of frequency inside the toroidicity-induced gap (and higher frequency gaps) exhibit three-wave coupling interactions with a zero-frequency fluctuation. The observation of the zero-frequency fluctuation is...
Transport of neutral beam generated fast ions in the presence of sawteeth is investigated experimentally at the DIII-D with a suite of newly developed imaging energetic particle diagnostics, which includes two Imaging Neutral Particle Analyzers (INPAs) and one Imaging Fast-Ion D-Alpha (IFIDA) diagnostic. The INPAs and IFIDA measure fast ions that charge exchange with injected beam neutrals and...
Recently, a hot-ion scenario characterized by a high fraction of fast ions, termed Fast Ion Regulated Enhancement (FIRE) mode, has been developed in KSTAR [1,2]. The FIRE mode has been sustained for several tens of seconds, achieving plasma performance comparable to the H-mode scenario (β_N ≈ 2 and H_89 ≈ 2.4). Power balance analysis and gyrokinetic simulations indicate that the enhanced...
The alpha particle should have good confinement when there are instabilities and toroidal field ripple in fusion devices. With the alpha particle slowing down distribution generated by TRANSP/NUBEAM, Alfven eigenfunction calculated by NOVA/NOVA-K, and a quasilinear model in the ORBIT code, the study investigated the nonlinear evolution of Toroidal Alfven Eigenmode (TAE) driven by alpha...
Extensive experimental [1, 2] and theoretical [3] works have recently demonstrated a strong interaction between energetic particles and Edge Localized Modes (ELMs). Hybrid kinetic-MHD simulations conducted with the MEGA code [4] revealed the key role that energetic particles kinetic effects have on the spatio-temporal structure of type-I ELMs in NBI heated discharges in the ASDEX Upgrade...
Internal Transport Barriers (ITBs) are regions in tokamak plasmas where reduced core transport leads to steep pressure gradients, indicating improved confinement. Moreover, the associated steep pressure gradients generate a high bootstrap current fraction, aiding plasma current drive and enabling potential steady-state operation. These advantages make ITBs important for advancing fusion energy...
ST40 is a high-field spherical tokamak with a major radius of 0.4 – 0.5 m and toroidal magnetic field up to 2.1 T. It is equipped with two NBI systems with 1.0 MW at 55 keV and 0.8 MW at 24 keV in deuterium. The high beam power density in a small machine produces a high fast particle fraction, confinement of which is critical for good plasma performance. Additionally, the high toroidal field...
Neutral Beam Injection (NBI) is a critical method for plasma heating in fusion devices [5, 3, 1]. While NBI has been extensively studied in tokamaks, its implementation in high-field stellarator configurations presents unique challenges and opportunities. Plasmas in future stellarator power plants will be larger and denser than those in current stellarators, requiring NBI to operate at higher...
High-field Spherical Tokamaks (STs) offer an attractive path to compact Fusion Power Plants (FPP). Extreme nuclear heating and power exhaust levels pose, however, severe engineering challenges due to their tight divertor wetted area and center columns. Negative Triangularity (NT) emerges as a promising solution for an integrated scenario with high fusion performance, minimal plasma-wall...
The nonlinear dynamics of Toroidal Alfvén Eigenmodes (TAEs) destabilized by the resonant interaction with trapped energetic particles, and to a lesser extent, non-standard copassing particles, are investigated using the HMGC code. Focusing on the low-shear Tokamak configuration adopted in the ITPA benchmark, the analysis employs the Hamiltonian-mapping approach, where the resonant phase-space...
In the advanced scenarios of future reactor burning plasmas, with a large fraction of non-inductive current maintained off-axis and the magnetic shear reversed in the plasma core region, multiple reversed shear Alfvén eigenmodes (RSAEs) could be excited by fusion alpha particles. Since RSAEs generally localize together around the SAW continuum extremum induced by the local minimum of the...
In magnetically confined fusion plasmas, shear Alfvén waves (SAWs) can be resonantly excited by energetic particles (EPs), and in turn, induce EP anomalous transport loss across magnetic surfaces, resulting in plasma performance degradation and possibly damage of plasma facing components. With the EP anomalous transport rate determined by the amplitude and spectrum of the SAW instabilities, it...
During the second Deuterium-Tritium campaign (DTE2) at the Joint European Torus (JET), critical physical phenomena relevant to ITER operations were extensively studied. Among these, the detection and analysis of fusion-born alpha particles were of particular importance due to their role in plasma self-heating [1, 2]. This work presents a novel diagnostic...
The behavior and confinement of fusion-born alpha particles are critical to the performance of magnetized deuterium-tritium (DT) plasmas. These alpha particles, produced in DT fusion reactions, emerge with energies primarily around 3.5 MeV, forming a narrow energy distribution. Initially, this results in an inverted velocity distribution, which can lead to the development of instabilities that...
The potential for ICRF accelerated energetic ions to drive vertical modes with toroidal mode number equal to zero ($𝑛_{\phi} = 0$) in tokamaks is explored. In particular, two effects are considered: (i) drive due to the highly anisotropic nature of the distribution function of ICRF accelerated ions; and (ii) pure “bump on tail” in the energy direction of the distribution function following...
The parallel motion and the perpendicular gyro-averaging operation are the most fundamental description of guiding centre (GC) dynamics in magnetic fusion plasmas. Though look straightforward, they contain two interesting aspects to be explored in the context of energetic particle dynamics, including potential applications. One is the appearance of the parallel GC drift (Ud) and the...
We present calculations of the orbit-space sensitivity of two-step reaction gamma-ray spectroscopy diagnostics, with arbitrary line-of-sight in toroidally symmetric magnetic equilibria. We consider the two-step reaction between alpha particles and beryllium-9, generating a neutron and an excited carbon-12, the latter of which then decays emitting an MeV photon. We show how the kinematics of...
Latest advancement of the design of the Fast-Ion Loss Detector (FILD) diagnostic for the ITER tokamak are detailed in this contribution. Advanced Hamiltonian full-orbits simulations are executed to estimate the velocity-space of the fast-ion fluxes on the diagnostic probe head. Using the ASCOT code, these fluxes are characterized for different spatial spectra of externally applied 3D fields...
A new perpendicular FIDA view for MAST-U has been implemented, which restores the dual view capability (including toroidal and vertical) possessed by the FIDA diagnostic on MAST [1], giving a view of the trapped particle regions of phase space and allowing for broader energy resolution because the Doppler shift of the beam emission is close to zero. The original vertical views were removed...
This work resolves three fundamental limitations of Tikhonov regularization, the current standard for fast-ion phase-space tomography: the ad hoc physical choice of regularization parameter, the incomplete treatment of model uncertainties, and the absence of error bounds derived from physics and model uncertainties. Each part is addressed in turn.
While various methods exist for determining...
A new artificial neural network was designed by modifying the neural ordinary differential equation (NODE) framework to successfully predict the time evolution of the 2-dimensional mode profile in both the linear growth stage and nonlinear saturated stage. Based on physical properties and symmetry considerations of the energetic-particle-driven geodesic acoustic mode (EGAM), simplifying...
Alfvén eigenmodes (AEs), driven by energetic particles, are critical for understanding the stability and performance of magnetically confined plasmas. With the recent installation of the tungsten divertor in the KSTAR tokamak, significant changes to plasma equilibrium, edge profiles, and energetic particle dynamics necessitate predictive simulations to anticipate experimental results and guide...
The SMall Aspect Ratio Tokamak (SMART) is a new Spherical Tokamak (ST) aimed at exploring the prospects of Negative Triangularity (NT) in STs and the potential of this combination for a future compact Fusion Power Plant (FPP) [1-3]. SMART has been designed to operate at Bt ≤ 1 T and Ip ≤ 0.5 MA with the magnetic axis, Rmag~ 0.4-0.6 m, and the plasma minor radius, a ~ 0.2-0.3 m with pulse...
Currently several new magnetically confined fusion experiments are being built or planned. Many plan to operate using deuterium-tritium fuel with the aim of studying the burning plasma physics regime. Numerical simulations related to fusion-born alpha particle confinement are playing a key role in optimising these experiments. Similarly, auxiliary heating schemes such as neutral beam ion...
Fast ion (FI) transport by Toroidal Alfven Eigenmodes (TAEs) is predicted to be of great importance in future tokamaks with high rates of deuterium-tritium fusion, since plasma self-heating capability relies on good confinement of fast alpha particles. Resonance between fast ions and TAEs occurs within distinct ‘resonance regions’ of phase space, which grow wider when the TAE mode amplitude...
Although collisionless guiding center trajectories are generally non-integrable in 3D magnetic fields, stellarators can be designed to have quasisymmetry. Recently, “precisely quasisymmetric” configurations have been obtained through numerical optimization, demonstrating excellent confinement of the guiding center trajectories of fusion-born alpha particles. There is, however, the potential...
Fast ions from neutral beam injection (NBI) or radiofrequency (RF) heating can resonantly interact with the background plasma and excite Alfvénic eigenmodes (AEs), leading to losses and potential damage to the reactor vessel [1]. Combined RF-NBI heating shows mixed effects on the Alfvénic activity at NSTX(-U) sometimes mitigating or exciting the modes [2-4]. An accurate knowledge of the RF–NBI...
Mitigation or prevention of runaway electron (RE) beam in the disruption phase is necessary for the safe operation of tokamaks. One of the strategies for RE mitigation is the resonant wave injection [1-3], limiting the parallel momentum of the RE. Single-particle analyses [2, 3] reveal that electron motion in an optimal coherent whistler wave is sensitive to the initial condition, and an...
Understanding the triggering and regulation mechanisms of energetic particle (EP) transport is a significant issue for magnetically confined plasmas. Toroidal Alfven eigenmode (TAE) can be driven unstable by EPs intrinsically existed in burning plasmas [1]. Nonlinear generation of zonal flows (ZFs) is a significant component for TAE self-regulation. Previous studies contain only effects of EPs...
We present a model of toroidal Alfvén eigenmode (TAE)-driven zonal modes (ZM) producing transport barriers in fusion plasmas. The model is constructed based on the scenarios where a sustained energetic particle source strongly drives toroidal Alfvén eigenmodes (TAE), and phase-space transport is insufficient to saturate TAE. With the sustained EP profile and strongly excited TAE, the...
The nonlinear saturation of energetic particle (EP)-driven instabilities has been extensively studied in Tokamak plasmas. Two main nonlinear mechanisms govern the saturation of these instabilities: wave-particle interactions and wave-wave nonlinearities. Wave-particle interactions are well described by the theoretical framework of the Berk-Breizman model [1], which explains how mode growth is...
The nonlinear stability characteristics and Alfvén instability driven transport are anticipated to have dominant effects in both tokamak and stellarator reactors. Based upon simulations with the 3D gyrofluid FAR3d model, we predict that EP populations will: drive significant levels of non classical EP transport; generate zonal flow shearing and zonal currents that impact thermal plasma...
Large-scale fusion devices such as ITER, as well as possible fusion reactors in the future, are expected to operate at steady state with a substantial non-inductive current fraction, which generally renders a reversed shear scenario. At this time, energetic particles (EPs), especially fusion alpha particles in the core region, will easily excite reversed shear Alfvén eigenmodes (RSAE). RSAE...
Sawtooth oscillations are one of the important MHD instabilities in tokamak plasmas. Previous studies have shown that they have different complex dynamic behaviors, which have important implications for the performance of fusion reactors. Energetic particles are believed to affect MHD instabilities and plasma confinement through various mechanisms, such as inducing zonal flows by...
In the magnetic confinement fusion devices, there are multiple fast ion species such as fusion product α-particles and fast deuterons produced by neutral beam injection (NBI). These fast ions may induce MHD instabilities such as Alfvén Eigenmodes (AEs) which enhance fast-ion transport and losses. The study of fast ion driven instabilities is one of the important topics for fusion reactors....
In the transition from L-mode to H-mode, a sheared plasma flow perpendicular to the magnetic field caused by the gradient of a local radial electric field Er is developed. This E × B flow is believed to be crucial for turbulence suppression and the formation of an edge transport barrier, which ultimately leads to better plasma performance. While this is well accepted, there is a long-standing...
A scintillating fast-ion loss detector [1] has successfully undergone its conceptual design review to be installed for the ITER D-T operation. The detector’s probe head, in its measuring position, is exposed to heat loads in the order of MW/m2. The thermal loads on the detector’s probe head under normal operational conditions have been determined using the SMITER code [2] for the thermal...
Energetic particles in nuclear fusion devices are essential for the heating of the plasma. The power deposition strongly depends on parameters of the plasma and equilibrium. However, uncertainties cannot be neglected. In that context, this work addresses how uncertainties in different parameters characterizing the plasma can impact the power deposition and the particle sources. We focus our...
The limited understanding of fast-ion distribution functions represents a
significant barrier to optimizing fusion performance. More than just increased diagnostic capabilities, any prior information, in addition to the measurement data, can significantly improve reconstructions of the distribution function. Here we present a method of using ASCOT simulations to help reconstruct the fast-ion...
Please see attached abstract.
We have developed a new full-orbit module for energetic particle simulations within a hybrid kinetic-MHD code, MEGA, incorporating the Boris method to enhance accuracy and stability in particle trajectory calculations. The evolution of the energetic particle distribution function was calculated using the δf method in guiding-center coordinates, facilitated by a transformation based on...
We conducted a code verification study to investigate the effects of fast ions on turbulence by comparing two gyrokinetic codes: GENE [F. Jenko et al., Phys. Plasmas 7, 1904-1910 (2000)] and CGYRO [J. Candy et al., J. Comput. Phys. 324, 73-93 (2016)]. Using L-mode plasma profiles from KSTAR, we performed local linear and nonlinear electromagnetic simulations to systematically assess the impact...
