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This paper summarizes the results presented at the 24th IAEA Fusion Energy Conference in the categories of plasma–material interactions, divertors, limiters, scrape-off layer (EX/D), stability (EX/S), wave–plasma interactions, current drive, heating, energetic particles (EX/W) in magnetic confinement experiments. In total, 149 papers including post-deadline papers have contributed to these categories. Several closely related papers, which are actually categorized in confinement (EX/C), have also been included. The understanding of experimental results has progressed remarkably, in particular, in the topics of resonant magnetic perturbation and ITER-like wall, which are the highlight of this conference. At the same time, identification of the bridging mechanism between the actuator and the consequence still requires further dedicated efforts so as to provide more accurate and reliable extrapolations to ITER and DEMO., source:To cite this article: H. Yamada 2013 Nucl. Fusion 53 104025, source:https://doi.org/10.1088/0029-5515/53/10/104025, identifier:0000-0003-4546-3167

Error fields are predominantly attributed to inevitable coil imperfections. Controlling error fields during coil fabrication and assembly is crucial for stellarators. Excessively tight coil tolerance increases time and cost, and, in part, led to the cancellation of the National Compact Stellarator Experiment and delay of W7-X. In this paper, we improve the recently proposed Hessian matrix method to rapidly identify important coil deviations. Two of the most common figures of merit, magnetic island size and quasi-symmetry, are analytically differentiated over coil parameters. By extracting the eigenvectors of the Hessian matrix, we can directly identify sensitive coil deviations in the order of the eigenvalues. The new method is applied to the upcoming Chinese First Quasi-axisymmetric Stellarator configuration. Important perturbations that enlarge n/m = 4/11 islands and deteriorate quasi-axisymmetry of the magnetic field are successfully determined. The results suggest each modular coil should have separate tolerance and some certain perturbation combinations will produce significant error fields. By relaxing unnecessary coil tolerance, this method will hopefully lead to a substantial reduction in time and cost., source:Caoxiang Zhu et al 2019 Nucl. Fusion 59 126007, source:https://doi.org/10.1088/1741-4326/ab3a7c, identifier:0000-0003-2337-3232

In this paper, we report new results of a beam switching experiment aiming at a reversed magnetic shear profile formation for the study of an MHD-mode-induced profile collapse event. A transient MHD mode, whose oscillation frequency chirps down, is observed. The electron temperature profile collapse is induced by the mode activity, leading to the flattening of the central electron temperature profile. The radial mode structure is the double-oddparity at the beginning, but it transits to the even-parity in its final stage. The central electron temperature profile recovers after the radial mode structure changes to the even-parity, even though the mode itself does not disappear., source:T. Kobayashi et al 2020 Nucl. Fusion 60 036017, source:https://doi.org/10.1088/1741-4326/ab6b40, identifier:0000-0001-5669-1937, identifier:0000-0003-3754-897X, identifier:0000-0001-7618-6305, identifier:0000-0002-0585-4561

The Fusion Engineering Research Project (FERP) at the National Institute for Fusion Science (NIFS) is conducting conceptual design activities for the LHD-type helical fusion reactor FFHR-d1A. This paper newly defines two design options, 'basic' and 'challenging.' Conservative technologies, including those that will be demonstrated in ITER, are chosen in the basic option in which two helical coils are made of continuously wound cable-in-conduit superconductors of Nb3Sn strands, the divertor is composed of water-cooled tungsten monoblocks, and the blanket is composed of water-cooled ceramic breeders. In contrast, new ideas that would possibly be beneficial for making the reactor design more attractive are boldly included in the challenging option in which the helical coils are wound by connecting high-temperature REBCO superconductors using mechanical joints, the divertor is composed of a shower of molten tin jets, and the blanket is composed of molten salt FLiNaBe including Ti powers to increase hydrogen solubility. The main targets of the challenging option are early construction and easy maintenance of a large and three-dimensionally complicated helical structure, high thermal efficiency, and, in particular, realistic feasibility of the helical reactor., source:https://doi.org/10.1088/1741-4326/aa6b12, identifier:0000-0002-5354-6619

In this paper, we elaborate the electric field excitation mechanism during the L–H transition in the JFT-2M tokamak. Using time derivative of the Poisson's equation, models of the radial electric field excitation is examined. The sum of the loss-cone loss current and the neoclassical bulk viscosity current is found to behave as the experimentally evaluated radial current that excites the radial electric field. The turbulent Reynolds stress only plays a minor role. The wave convection current that produces a negative current at the edge can be important to explain the ambipolar condition in the L-mode., source:Citation T. Kobayashi et al 2017 Nucl. Fusion 57 072005, source:https://doi.org/10.1088/1741-4326/aa5d03, identifier:0000-0001-5669-1937

In this paper, we investigate data from the density scan experiment in order to clarify how the transport hysteresis width depends on the density. As the line averaged density increases, the hysteresis width almost monotonically decreases. To discuss the physical mechanism of the hysteresis formation, a theoretical model describing the direct response of the fluctuation amplitude to the heating is examined. The model predicts that decreasing density enhances the hysteresis width in the turbulent thermal transport, which is not in contradiction with the present observation. It is found that the model tends to estimate the parameter window in which the hysteresis emerges narrower than the experimental observation., source:Citation T. Kobayashi et al 2018 Nucl. Fusion 58 126031, source:https://doi.org/10.1088/1741-4326/aae5de, identifier:0000-0001-5669-1937

A new approach for inducing a thermal transport model, of ion heat diffusivity as an example, for magnetically confined high-temperature plasmas has been further pursued after its initial proposal by Yokoyama (2014 Plasma Fusion Res. 9 1302137). It has been based on a statistical approach utilizing the accumulated experimental transport analyses database. Two approaches are described in this paper: (1) placing a priority on reproducing the ion heat diffusivity with higher accuracy for better reproduction of ion temperature profiles, and (2) attempting to acquire a physics interpretation through variable selections and the dependence of the ion heat diffusivity on them. Such progress will foster the study of a practical transport model for real-time control and the provision for guidance to the parameter dependence to be pursued by large-scale cutting-edge simulations., source:Citation M. Yokoyama 2019 Nucl. Fusion 59 094004, source:https://doi.org/10.1088/1741-4326/ab31db

Progress of statistical modelling of thermal transport of fusion plasmas based on (2–4 a) a transport analysis database is described. Statistically induced ion and electron thermal diffusivities are checked with an actual discharge which had not been included in the database. Usefulness of this statistical approach is explained in terms of (1) extracting important parameters through the application of information criterion, and (2) making possible for discussing exponents of regression expression and then implying the thermal transport property. The statistical approach reported in this paper could provide a new insight for thermal transport modelling for fusion plasmas, complementing conventional global scalings on the energy confinement time., source:Citation M. Yokoyama and H. Yamaguchi 2020 Nucl. Fusion 60 106024, source:https://doi.org/10.1088/1741-4326/abac6a, identifier:0000-0001-8856-1483

Achieving impurity and helium ash control is a crucial issue in the path towards fusion-grade magnetic confinement devices, and this is particularly the case of helical reactors, whose low-collisionality ion-root operation scenarios usually display a negative radial electric field which is expected to cause inwards impurity pinch. In this work we discuss, based on experimental measurements and standard predictions of neoclassical theory, how plasmas of very low ion collisionality, similar to those observed in the impurity hole of the large helical device (Yoshinuma et al and The LHD Experimental Group 2009 Nucl. Fusion 49 062002, Ida et al and The LHD Experimental Group 2009 Phys. Plasmas 16 056111 and Yokoyama et al and LHD Experimental Group 2002 Nucl. Fusion 42 143), can be an exception to this general rule, and how a negative radial electric field can coexist with an outward impurity flux. This interpretation is supported by comparison with documented discharges available in the International Stellarator-Heliotron Profile Database, and it can be extrapolated to show that achievement of high ion temperature in the core of helical devices is not fundamentally incompatible with low core impurity content., source:Paper Moderation of neoclassical impurity accumulation in high temperature plasmas of helical devices J.L. Velasco1, I. Calvo1, S. Satake2,3, A. Alonso1, M. Nunami2,3, M. Yokoyama2,3, M. Sato2, T. Estrada1, J.M. Fontdecaba1, M. Liniers1, K.J. McCarthy1, F. Medina1, B. Ph Van Milligen1, M. Ochando1, F. Parra4,5, H. Sugama2, A. Zhezhera6, The LHD Experimental Team2 and The TJ-II Team1Hide full author list Published 27 October 2016 • © 2016 EURATOM Nuclear Fusion, Volume 57, Number 1 Citation J.L. Velasco et al 2017 Nucl. Fusion 57 016016, source:https://doi.org/10.1088/0029-5515/57/1/016016

The heat flux is one of the key parameter used to quantify and understand transport in fusion devices. In this paper, a new method is introduced to calculate the heat flux including its confidence with high accuracy based on perturbed measurements such as the electron temperature. The new method is based on ideal filtering to optimally reduce the noise contributions on the measurements and piece-wise polynomial approximations to calculate the time derivative. Both methods are necessary to arrive at a heat flux and effective diffusion coefficient with high accuracy. The new methodology is applied to a measurement example using electron cyclotron resonance heating block-wave modulation at the Large Helical Device showing the merit of the newly developed methodology., source:Citation M. van Berkel et al 2018 Nucl. Fusion 58 096036, source:https://doi.org/10.1088/1741-4326/aad13e, identifier:0000-0001-6574-3823

Energetic particles are inherent to toroidal fusion systems and can drive instabilities in the Alfvén frequency range, leading to decreased heating efficiency, high heat fluxes on plasma-facing components, and decreased ignition margin. The applicability of global gyrokinetic simulation methods to macroscopic instabilities has now been demonstrated and it is natural to extend these methods to 3D configurations such as stellarators, tokamaks with 3D coils and reversed field pinch helical states. This has been achieved by coupling the GTC global gyrokinetic PIC model to the VMEC equilibrium model, including 3D effects in the field solvers and particle push. This paper demonstrates the application of this new capability to the linearized analysis of Alfvénic instabilities in the LHD stellarator. For normal shear iota profiles, toroidal Alfvén instabilities in the n = 1 and 2 toroidal mode families are unstable with frequencies in the 75 to 110 kHz range. Also, an LHD case with non-monotonic shear is considered, indicating reductions in growth rate for the same energetic particle drive. Since 3D magnetic fields will be present to some extent in all fusion devices, the extension of gyrokinetic models to 3D configurations is an important step for the simulation of future fusion systems., source:Citation D.A. Spong et al 2017 Nucl. Fusion 57 086018, source:https://doi.org/10.1088/1741-4326/aa7601, identifier:0000-0003-2370-1873

0000-0003-2337-3232, Error fields are predominantly attributed to inevitable coil imperfections. Controlling error fields during coil fabrication and assembly is crucial for stellarators. Excessively tight coil tolerance increases time and cost, and, in part, led to the cancellation of the National Compact Stellarator Experiment and delay of W7-X. In this paper, we improve the recently proposed Hessian matrix method to rapidly identify important coil deviations. Two of the most common figures of merit, magnetic island size and quasi-symmetry, are analytically differentiated over coil parameters. By extracting the eigenvectors of the Hessian matrix, we can directly identify sensitive coil deviations in the order of the eigenvalues. The new method is applied to the upcoming Chinese First Quasi-axisymmetric Stellarator configuration. Important perturbations that enlarge n/m = 4/11 islands and deteriorate quasi-axisymmetry of the magnetic field are successfully determined. The results suggest each modular coil should have separate tolerance and some certain perturbation combinations will produce significant error fields. By relaxing unnecessary coil tolerance, this method will hopefully lead to a substantial reduction in time and cost.