Full wave propagation modelling in view to integrated ICRH wave coupling/RF sheaths modelling

RF sheaths rectification can be the reason for operational limits for Ion Cyclotron Range of Frequencies (ICRF) heating systems via impurity production or excessive heat loads. To simulate this process in realistic geometry, the Self-consistent Sheaths and Waves for Ion Cyclotron Heating (SSWICH) code is a minimal set of coupled equations that computes self-consistently wave propagation and DC plasma biasing. The present version of its wave propagation module only deals with the Slow Wave assumed to be the source of RF sheath oscillations. However the ICRF power coupling to the plasma is due to the fast wave (FW). This paper proposes to replace this one wave equation module by a full wave module in either 2D or 3D as a first step towards integrated modelling of RF sheaths and wave coupling. Since the FW is propagative in the main plasma, Perfectly Matched Layers (PMLs) adapted for plasmas were implemented at the inner side of the simulation domain to absorb outgoing waves and tested numerically with tilted BD in Cartesian geometry, by either rotating the cold magnetized plasma dielectric tensors in 2D or rotating the coordinate vector basis in 3D. The PML was further formulated in cylindrical coordinates to account for for the toroidal curvature of the plasma. Toroidal curvature itself does not seem to change much the coupling. A detailed 3D geometrical description of Tore Supra and ASDEX Upgrade (AUG) antennas was included in the coupling code. The full antenna structure was introduced, since its toroidal symmetry with respect to the septum plane is broken (FS bars, toroidal phasing, non-symmetrical structure). Reliable convergence has been obtained with the density profile up to the leading edge of antenna limiters. Parallel electric field maps have been obtained as an input for the present version of SSWICH

Sequential modelling of ICRF wave near RF fields and asymptotic RF sheaths description for AUG ICRF antennas

A sequence of simulations is performed with RAPLICASOL and SSWICH to compare two AUG ICRF antennas. RAPLICASOL outputs have been used as input to SSWICH-SW for the AUG ICRF antennas. Using parallel electric field maps and the scattering matrix produced by RAPLICASOL, SSWICH-SW, reduced to its asymptotic part, is able to produce a 2D radial/poloidal map of the DC plasma potential accounting for the antenna input settings (total power, power balance, phasing). Two models of antennas are compared: 2-strap antenna vs 3-strap antenna. The 2D DC potential structures are correlated to structures of the parallel electric field map for different phasing and power balance. The overall DC plasma potential on the 3-strap antenna is lower due to better global RF currents compensation. Spatial proximity between regions of high RF electric field and regions where high DC plasma potentials are observed is an important factor for sheath rectification

Characterization of 3-strap antennas in ASDEX Upgrade

The response of the local RF current measured at limiters of 3-strap ICRF antenna to variations of power balance and phasing at fICRF=30MHz agrees qualitatively well with EM calculations by TOPICA and RAPLICASOL codes. Measurements of tungsten sputtering yield and DC current at the limiters correlate strongly with the local RF current. In contrast to findings for the 2-strap antennas, values of DC current are predominantly positive, and negative only for some locations and feeding parameters. Explanations can involve more physical mechanisms than only parallel sheath dynamics

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

Ion cyclotron wall conditioning experiments on Tore Supra in presence of the toroidal magnetic field

Wall conditioning techniques applicable in the presence of the high toroidal magnetic field will be required for the operation of ITER for tritium removal, isotopic ratio control and recovery to normal operation after disruptions. Recently ion cyclotron wall conditioning (ICWC) experiments have been carried out on Tore Supra in order to assess the efficiency of this technique in ITER relevant conditions. The ICRF discharges were operated in He/H-2 Mixtures at the Tore Supra nominal field (3.8 T) and a RF frequency of 48 MHz, i.e. within the ITER operational space. RF pulses of 60 s (max.) were applied using a standard Tore Supra two-strap resonant double loop antenna in ICWC mode, operated either in pi or 0-phasing with a noticeable improvement of the RF coupling in the latter case. In order to assess the efficiency of the technique for the control of isotopic ratio the wall was first preloaded using a D-2 glow discharge. After 15 minutes of ICWC in He/H-2 gas mixtures the isotopic ratio was altered from 4% to 50% at the price of an important H implantation into the walls. An overall analysis comparing plasma production and the conditioning efficiency as a function of discharge parameters is given

Development of pre-conceptual ITER-type ICRF antenna design for DEMO

ICRF antenna development for DEMO for the pre-conceptual phase is carried out by merging the existing knowledge about multi-strap ITER, JET and ASDEX Upgrade antennas. Many aspects are taken over and adapted to DEMO, including the mechanical design and RF performance optimization strategies. The minimization of ICRF-specific plasma-wall interactions is aimed at by optimizing the feeding power balance, a technique already proven in practice. Technological limits elaborated for the components of ITER ICRF system serve as a guideline in the current design process. Several distinctive aspects, like antenna mounting, integration with the neighbouring components or adaptation for neutron environment, are tackled individually for DEMO

Recent progress on improving ICRF coupling and reducing RF-specific impurities in ASDEX Upgrade

The recent scientific research on ASDEX Upgrade (AUG) has greatly advanced solutions to two issues of Radio Frequency (RF) heating in the Ion Cyclotron Range of Frequencies (ICRF): (a) the coupling of ICRF power to the plasma is significantly improved by density tailoring with local gas puffing; (b) the release of RF-specific impurities is significantly reduced by minimizing the RF near field with 3-strap antennas. This paper summarizes the applied methods and reviews the associated achievements