Effect of impurities on the transition between minority ion and mode conversion ICRH heating in (3He)-H tokamak plasmas

Hydrogen majority plasmas will be used in the initial non-activated phase of ITER operation. Optimizing ion cyclotron resonance heating (ICRH) in such scenarios will help in achieving H-mode in these plasmas. Past JET experiments with the carbon wall revealed a significant impact of intrinsic impurities on the ICRH performance in (3He)-H plasmas relevant for the full-field initial ITER phase. High plasma contamination with carbon impurities resulted in the appearance of a supplementary mode conversion layer and significant reduction in the transition concentration of 3He minority ions, defined as the concentration at which the change from minority heating to mode conversion regime occurs. In view of the installation of the new ITER-like wall at JET, it is important to evaluate the effect of Be and W impurities on ICRH scenarios in (3He)-H plasmas. In this paper, an approximate analytical expression for the transition concentration of 3He minority ions is derived as a function of plasma and ICRH parameters, and accounting for typical impurity species at JET. The accompanying 1D wave modeling supports the analytical results and suggests a potential experimental method to reduce 3He level needed to achieve a specific heating regime by puffing a small amount of 4He ions additionally to (3He)-H plasma.Comment: 23 pages, 9 figure

Progress with applications of three-ion ICRF scenarios for fusion research: A review

Proceedings of the 24TH TOPICAL CONFERENCE ON RADIO-FREQUENCY POWER IN PLASMAS 26–28 September 2022 Annapolis, USAThe viability of magnetic confinement fusion as an energy source depends on achieving the high ion temperatures required for D-T fusion. Among the available techniques, plasma heating with waves in the ion cyclotron range of frequencies (ICRF) is a prominent method for bulk ion heating in fusion plasmas. Furthermore, a detailed understanding of the non-linear physics of alpha heating and the complex impact of MeV-range fast ions on plasma dynamics becomes progressively more important. This paper provides a comprehensive overview of recent developments with the three-ion ICRF scenarios on Alcator C-Mod, ASDEX Upgrade and JET tokamaks. The results demonstrate the flexibility of these novel scenarios for heating bulk ions in D-T ≈ 50%-50% plasmas and efficient generation of MeV-range fast ions in multi-ion species plasmas. Several key results relevant for ITER and future fusion reactors are highlighted.This work has been carried out within the framework of the EUROfusion Consortium, funded by the European Union via the Euratom Research and Training Programme (Grant Agreement No 101052200 – EUROfusion). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Commission. Neither the European Union nor the European Commission can be held responsible for them. We thank the ITPA Energetic Particle Physics Topical Group for its support. Part of this work was also carried out in the framework of projects done for the ITER Scientist Fellow Network (ISFN). ITER is the Nuclear Facility INB No. 174. The views and opinions expressed herein do not necessarily reflect those of the ITER Organization. This publication is provided for scientific purposes only. Its contents should not be considered as commitments from the ITER Organization as a nuclear operator in the frame of the licensing process.Peer Reviewed"Article signat per 78 autors/es: Ye. O. Kazakov; J. Ongena; M. Nocente; V. Bobkov; J. Garcia; V. G. Kiptily; M. Schneider; S. Wukitch; J. C. Wright; M. Dreval; K. K. Kirov; S. Mazzi; R. Ochoukov; S. E. Sharapov; Ž. Štancar; H. Weisen; Y. Baranov; M. Baruzzo; A. Bierwage; R. Bilato; A. Chomiczewska; R. Coelho; T. Craciunescu; K. Crombé; E. Delabie; E. de la Luna; R. Dumont; P. Dumortier; F. Durodié; J. Eriksson; M. Fitzgerald; J. Galdon-Quiroga; D. Gallart; M. Garcia-Munoz; L. Giacomelli; C. Giroud; J. Gonzalez-Martin; A. Hakola; R. Henriques; P. Jacquet; I. Jepu; T. Johnson; A. Kappatou; D. Keeling; D. King; C. Klepper; Ph. Lauber; M. Lennholm; E. Lerche; B. Lomanowski; C. Lowry; M. J. Mantsinen; M. Maslov; S. Menmuir; I. Monakhov; F. Nabais; M. F. F. Nave; C. Noble; E. Panontin; S. D. Pinches; A. R. Polevoi; D. Rigamonti; A. Sahlberg; M. Salewski; P. A. Schneider; H. Sheikh; K. Shinohara; P. Siren; S. Sumida; A. Thorman; R. A. Tinguely; D. Valcarcel; D. Van Eester; M. Van Schoor; J. Varje; M. Weiland; N. Wendler; JET Contributors, the ASDEX Upgrade Team and the EUROfusion MST1 Team"Postprint (author's final draft

Predictive simulations of NBI ion power load to the ICRH antenna in Wendelstein 7-X

In Wendelstein 7-X (W7-X), a new ion cyclotron resonance heating (ICRH) antenna will be commissioned during the operational campaign OP2.1. The antenna will have to sustain power loads not only from thermal plasma and radiation but also fast ions. Predictive simulations of fast-ion power loads to the antenna components are therefore important to establish safe operational limits. In this work, the fast-ion power loads from the W7-X neutral beam injection (NBI) system to the ICRH antenna was simulated using the ASCOT suite of codes. Five reference magnetic configurations and five antenna positions were considered to provide an overview of power load behavior under various operating conditions. The NBI power load was found to have an exponential dependence on the antenna insertion depth. Differences between magnetic configurations were significant, with the antenna limiter power load varying between 380 W and 100 kW depending on the configuration. Qualitative differences in power load patterns between configurations were also observed, with the low mirror and low iota configurations exhibiting higher loads to the sensitive antenna straps. The local fast-ion power flux to the antenna limiter was also considered and found to exceed the 2.0 MW m−2 steady-state safety limit only in specific cases. The NBI system might thus pose a safety concern to the ICRH antenna during concurrent NBI-ICRH operation, but additional heat propagation simulations of antenna components are needed to establish more realistic operational time limits

Efficient generation of energetic ions in multi-ion plasmas by radio-frequency heating

We describe a new technique for the efficient generation of high-energy ions with electromagnetic ion cyclotron waves in multi-ion plasmas. The discussed three-ion scenarios are especially suited for strong wave absorption by a very low number of resonant ions. To observe this effect, the plasma composition has to be properly adjusted, as prescribed by theory. We demonstrate the potential of the method on the world-largest plasma magnetic confinement device, JET (Joint European Torus, Culham, UK), and the high-magnetic-field tokamak Alcator C-Mod (Cambridge, USA). The obtained results demonstrate efficient acceleration of He-3 ions to high energies in dedicated hydrogendeuterium mixtures. Simultaneously, effective plasma heating is observed, as a result of the slowing-down of the fast He-3 ions. The developed technique is not only limited to laboratory plasmas, but can also be applied to explain observations of energetic ions in space-plasma environments, in particular, He-3-rich solar flares.Peer reviewe

Modelling of advanced three-ion ICRF heating and fast ion generation scheme for tokamaks and stellarators

Absorption of ion-cyclotron range of frequencies waves at the fundamental resonance is an efficient source of plasma heating and fast ion generation in tokamaks and stellarators. This heating method is planned to be exploited as a fast ion source in the Wendelstein 7-X stellarator. The work presented here assesses the possibility of using the newly developed three-ion species scheme (Kazakov et al (2015) Nucl. Fusion 55 032001) in tokamak and stellarator plasmas, which could offer the capability of generating more energetic ions than the traditional minority heating scheme with moderate input power. Using the SCENIC code, it is found that fast ions in the MeV range of energy can be produced in JET-like plasmas. The RF-induced particle pinch is seen to strongly impact the fast ion pressure profile in particular. Our results show that in typical high-density W7-X plasmas, the three-ion species scheme generates more energetic ions than the more traditional minority heating scheme, which makes three-ion scenario promising for fast-ion confinement studies in W7-X

4D and 5D phase-space tomography using slowing-down physics regularization

We compute reconstructions of 4D and 5D fast-ion phase-space distribution functions in fusion plasmas from synthetic projections of these functions. The fast-ion phase-space distribution functions originating from neutral beam injection (NBI) at TCV and Wendelstein 7-X (W7-X) at full, half, and one-third injection energies can be istinguished and particle densities of each component inferred based on 20 synthetic spectra of projected velocities at TCV and 680 at W7-X. Further, we demonstrate that an expansion into a basis of slowing-down distribution functions is equivalent to regularization using slowing-down physics as prior information. Using this technique in a Tikhonov formulation, we infer the particle density fractions for each NBI energy for each NBI beam from synthetic measurements, resulting in six unknowns at TCV and 24 unknowns at W7-X. Additionally, we show that installing 40 LOS in each of 17 ports at W7-X, providing full beam coverage and almost full angle coverage, produces the highest quality reconstructions

Justification of increasing the blood flow velocity in the arteries of the thyroid gland in autoimmune thyroiditis as a reflection of endothelial changes due to inflammatory status

Abstract: Objective: The aim of the research was to determine the dependence of the blood flow velocity in the thyroid arteries in patients with autoimmune thyroiditis (AIT) on the presence of atherosclerotic carotid disease and the level of systemic blood pressure. Method: The research involved 20 patients with AIT in euthyroid state, 30 patients AIT in euthyroid state with stable coronary heart disease (CHD), 30 patients with stable CHD and 30 healthy individuals. Participants of the research were examined using ultrasound of carotid arteries and inferior thyroid arteries. Parameters of blood flow velocity were compared with the level of systemic blood pressure. Results: In AIT peak systolic velocity and resistance index in the inferior thyroid arteries were sig- nificantly higher than in healthy individuals and patients with CHD (p<0.05). In patients with CHD velocity parameters in carotid arteries were high, unlike in the healthy individuals and patients with AIT (p<0.05). In patients with AIT without CHD the atherosclerotic changes of carotid arteries were not found. Increased systemic blood pressure was noticed in all patients with CHD without significant differences between groups

Study of fast-ion-driven toroidal Alfvén eigenmodes impacting on the global confinement in TCV L-mode plasmas

Following recent observations of unstable Toroidal Alfvén Eigenmodes (TAEs) in a counter-current Neutral Beam Injection (NBI) scenario developed in TCV, an in-depth analysis of the impact of such modes on the global confinement and performance is carried out. The study shows experimental evidence of non-degradation of ion thermal confinement despite the increasing of auxiliary power. During such an improved confinement period, Toroidal Alfvén Eigenmodes (TAEs) driven by fast ions generated through Neutral Beam Injection (NBI) are found unstable. Together with the TAEs, various instabilities associated with the injection of the fast neutrals are observed by multiple diagnostics, and a first characterization is given. Nonlinear wave-wave couplings are also detected through multi-mode analysis, revealing a complex picture of the stability dynamics of the TCV scenario at hand. The measurements provided by a short-pulse reflectometer corroborate the identification and radial localization of the instabilities. A preliminary, but not conclusive, analysis of the impact of TAEs on the amplitude of the electron density fluctuations is carried out. Local flux-tube gyrokinetic simulations show that the dominant underlying instabilities in the absence of fast ions are Trapped Electron Modes (TEM), and that these modes are effectively suppressed by zonal flows. Attempts to simulate the simultaneous presence of fast-ion driven TAEs and TEM turbulence show that elongated streamers develop up to the full radial extent of the flux-tube domain, thereby invalidating the local assumption and indicating that a global approach is mandatory in these TCV plasmas