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The mode structure symmetry breaking is important for the understanding of the momentum transport induced by micro turbulence and the experimental observation of Alfvénic mode structures driven by energetic particles (EPs) as well as the burning plasma behavior. In this work, the theoretical approach for the analyzes of the global mode structure in the presence of EPs is introduced with various applications. As a brief review of our previous work, the calculation of strongly coupled poloidal harmonics, with a complex ‘tilting angle’ applied, and the calculation of weakly coupled poloidal harmonics, with EPs’ non-perturbative effects taken into account, are introduced. By making use of the theoretical approach, several applications related to the mode structure symmetry breaking are demonstrated. The anisotropic EP impact on the zonal flow residual is calculated. The mode structure symmetry breaking of the EP induced geodesic acoustic mode is studied. The momentum transport related to the mode structure symmetry breaking is estimated. The particle and energy transport is also analyzed and its comparison with the turbulence induced transport is discussed. [ABSTRACT FROM AUTHOR]

The progress made in understanding spontaneous toroidal rotation reversals in tokamaks is reviewed and current ideas to solve this ten-year-old puzzle are explored. The paper includes a summarial synthesis of the experimental observations in AUG, C-Mod, KSTAR, MAST and TCV tokamaks, reasons why turbulent momentum transport is thought to be responsible for the reversals, a review of the theory of turbulent momentum transport and suggestions for future investigations. [ABSTRACT FROM AUTHOR]

The most recent experiments of disruption mitigation by massive gas injection in ASDEX Upgrade have concentrated on small—relatively to the past—quantities of noble gas injected, and on the search for the minimum amount of gas necessary for the mitigation of the thermal loads on the divertor and for a significant reduction of the vertical force during the current quench. A scenario for the generation of a long-lived runaway electron beam has been established; this allows the study of runaway current dissipation by moderate quantities of argon injected. This paper presents these recent results and discusses them in the more general context of physical models and extrapolation, and of the open questions, relevant for the realization of the ITER disruption mitigation system. [ABSTRACT FROM AUTHOR]

A 0D analytical stationary model to estimate the degree of detachment on the divertor plates is derived, starting from previous works of Igitkhanov (Igitkhanov et al 1994 21st EPS (Montpellier) ECA v.18B, 1995 22th EPS (Bournemouth) ECA v.19C, Igitkhanov 2014 KIT Sci. Rep. 7661). It accounts for heat convection, conduction, impurity radiation and contains a simplified balance for the neutrals. The upstream particle flux (or, alternatively, the density upstream nup), the heat flux in the scrape-off layer (SOL) qup and the impurity concentrations are required as input, whereas the temperatures at the plate and at the separatrix are not fixed a priori. The routine has been mainly developed for system codes, or more in general for scopy studies in the framework of the preliminary design phase for the reactor DEMO, its simplicity being therefore justified by the purpose of keeping the calculation times as low as possible. A calibration against a more detailed 1D routine (Kallenbach et al 2016 Plasma Phys. Control. Fusion58 045013) has been performed, finding a reasonable agreement. Furthermore, a coupling of the model with the 1.5D transport code ASTRA (Pereverzev 1991 IPP Report 5/42, Fable et al 2013 Plasma Phys. Control. Fusion55 124028) to illustrate its possible usage is also presented. [ABSTRACT FROM AUTHOR]

In systems modelling for fusion power plants, it is essential to robustly predict the performance of a given machine design (including its respective operating scenario). One measure of machine performance is the energy confinement time that is typically predicted from experimentally derived confinement scaling laws (e.g. IPB98(y,2)). However, the conventionally used scaling laws have been derived for ITER which—unlike a fusion power plant—will not have significant radiation inside the separatrix. In the absence of a new high core radiation relevant confinement scaling, we propose an ad hoc correction to the loss power used in the ITER confinement scaling and the calculation of the stored energy by the radiation losses from the ‘core’ of the plasma . Using detailed ASTRA / TGLF simulations, we find that an appropriate definition of is given by 60% of all radiative losses inside a normalised minor radius . We consider this an improvement for current design predictions, but it is far from an ideal solution. We therefore encourage more detailed experimental and theoretical work on this issue. [ABSTRACT FROM AUTHOR]

A toroidal momentum transport equation is presented, which is suited for implementation in 1D transport codes in axisymmetric geometry (e.g. tokamak plasmas). Contributions to the total toroidal momentum from the different plasma species are retained. The contributions of E × B, diamagnetic and poloidal flows are also retained. The different pieces appearing in the expression for the turbulence-driven part of the flux are obtained consistently from standard gyro-kinetic theory. [ABSTRACT FROM AUTHOR]

The confinement fast ions, generated by neutral beam injection (NBI), has been investigated at the ASDEX Upgrade tokamak. In plasmas that exhibit strong sawtooth crashes, a significant sawtooth-induced internal redistribution of mainly passing fast ions is observed, which is in very good agreement with the theoretical predictions based on the Kadomtsev model. Between the sawtooth crashes, the fishbone modes are excited which, however, do not cause measurable changes in the global fast-ion population. During experiments with on- and off-axis NBI and without strong magnetohydrodynamic (MHD) modes, the fast-ion measurements agree very well with the neo-classical predictions. This shows that the MHD-induced (large-scale), as well as a possible turbulence-induced (small-scale) fast-ion transport is negligible under these conditions. However, in discharges performed to study the off-axis NBI current drive efficiency with up to 10 MW of heating power, the fast-ion measurements agree best with the theoretical predictions that assume a weak level anomalous fast-ion transport. This is also in agreement with measurements of the internal inductance, a Motional Stark Effect diagnostic and a novel polarimetry diagnostic: the fast-ion driven current profile is clearly modified when changing the NBI injection geometry and the measurements agree best with the predictions that assume weak anomalous fast-ion diffusion. [ABSTRACT FROM AUTHOR]

The neoclassical transport of tungsten in the H-mode edge transport barrier (ETB) of ITER is investigated and scaling relations for the transport coefficients are evaluated. The major finding is that the radial convection velocity of tungsten is outward directed for a large proportion of the tested pedestal profiles. This is due to a combination of the high pedestal temperatures and the high separatrix densities making the outward directed temperature screening term the predominant contribution of the collisional convection. The high densities at the separatrix are needed to control the power exhaust and the tungsten sputtering in the divertor and the high pedestal temperatures are expected to be achieved in ITER to meet its fusion performance objectives. The density and temperature profiles, which deliver simultaneously optimum fusion performance, power exhaust and tungsten sputtering control in ITER, also ensure optimum collisional radial transport of tungsten leading to hollow tungsten density profiles in the ETB. In helium H-mode plasmas, which are considered for the initial ITER non-active operation, this very favourable neoclassical transport effect is reduced and only about half of the considered edge plasma profiles yield an outward directed drift. [ABSTRACT FROM AUTHOR]

Using the local (flux-tube) version of the Eulerian code GENE (Jenko et al 2000 Phys. Plasmas 7 1904), gyrokinetic simulations of microturbulence were carried out considering parameters relevant to electron-internal transport barriers (e-ITBs) in the TCV tokamak (Sauter et al 2005 Phys. Rev. Lett. 94 105002), generated under conditions of low or negative shear. For typical density and temperature gradients measured in such barriers, the corresponding simulated fluctuation spectra appears to simultaneously contain longer wavelength trapped electron modes (TEMs, for typically k[?]ri 0.5). The contributions to the electron particle flux from these two types of modes are, respectively, outward/inward and may cancel each other for experimentally realistic gradients. This mechanism may partly explain the feasibility of e-ITBs. The non-linear simulation results confirm the predictions of a previously developed quasi-linear model (Fable et al 2010 Plasma Phys. Control. Fusion 52 015007), namely that the stationary condition of zero particle flux is obtained through the competitive contributions of ITG and TEM. A quantitative comparison of the electron heat flux with experimental estimates is presented as well. [ABSTRACT FROM AUTHOR]

Global plasma oscillations, involving electron temperature, plasma density and current, have been observed during electron cyclotron current driven ECCD discharges on TCV (Tokamak à Configuration Variable; R/a = 0.88 m/0.25 m, k [?] 2.8, BT < 1.54 T). This is confirmed by multiple diagnostics operating on different physical principles: electron cyclotron emission radiometer, soft x-ray, far-infrared reflectometer, bolometer and magnetic probes. The oscillations develop in the presence of electron internal transport barriers and reversed magnetic shear. They are reminiscent of the central electron temperature oscillations (the so-called O-regime) seen in low-loop voltage or fully non-inductive lower-hybrid current driven plasmas with reversed central magnetic shear on Tore Supra (Giruzzi et al 2003 Phys. Rev. Lett. 91 935001). The oscillations have m/n = 0/0 periodicity and are not the manifestation of a magnetohydrodynamic (MHD) instability in itself, but they are invariably linked to the presence of MHD modes on TCV. In fact, no plasma discharge has been obtained so far displaying oscillations in the absence of MHD activity. The interaction of the oscillations with MHD can play a strong role in the coupled dynamics of heat and current transport, as the modes can significantly perturb the q profile. More generally the presence of MHD modes can aid in the correct identification of rational q-surfaces [4]. The interplay between MHD and the plasma oscillations, with the first being the cause for the development of the second, is the main focus of this paper. It is also shown that the global oscillations can be removed by adding an Ohmic current perturbation and therefore by modifying the current density profile. [ABSTRACT FROM AUTHOR]