We present an ultrafast neural network (NN) model, QLKNN, which predicts core tokamak transport heat and particle fluxes. QLKNN is a surrogate model based on a database of 300 million flux calculations of the quasilinear gyrokinetic transport model QuaLiKiz. The database covers a wide range of realistic tokamak core parameters. Physical features such as the existence of a critical gradient for the onset of turbulent transport were integrated into the neural network training methodology. We have coupled QLKNN to the tokamak modelling framework JINTRAC and rapid control-oriented tokamak transport solver RAPTOR. The coupled frameworks are demonstrated and validated through application to three JET shots covering a representative spread of H-mode operating space, predicting turbulent transport of energy and particles in the plasma core. JINTRAC-QLKNN and RAPTOR-QLKNN are able to accurately reproduce JINTRAC-QuaLiKiz T i,e and n e profiles, but 3 to 5 orders of magnitude faster. Simulations which take hours are reduced down to only a few tens of seconds. The discrepancy in the final source-driven predicted profiles between QLKNN and QuaLiKiz is on the order 1%-15%. Also the dynamic behaviour was well captured by QLKNN, with differences of only 4%-10% compared to JINTRAC-QuaLiKiz observed at mid-radius, for a study of density buildup following the L-H transition. Deployment of neural network surrogate models in multi-physics integrated tokamak modelling is a promising route towards enabling accurate and fast tokamak scenario optimization, Uncertainty Quantification, and control applications.

A power-balance model, with radiation losses from impurities and neutrals, gives a unified description of the density limit (DL) of the stellarator, the L-mode tokamak, and the reversed field pinch (RFP). The model predicts a Sudo-like scaling for the stellarator, a Greenwald-like scaling, , for the RFP and the ohmic tokamak, a mixed scaling, , for the additionally heated L-mode tokamak. In a previous paper (Zanca et al 2017 Nucl. Fusion 57 056010) the model was compared with ohmic tokamak, RFP and stellarator experiments. Here, we address the issue of the DL dependence on heating power in the L-mode tokamak. Experimental data from high-density disrupted L-mode discharges performed at JET, as well as in other machines, are taken as a term of comparison. The model fits the observed maximum densities better than the pure Greenwald limit.

The 2014–2016 JET results are reviewed in the light of their significance for optimising the ITER research plan for the active and non-active operation. More than 60 h of plasma operation with ITER first wall materials successfully took place since its installation in 2011. New multi-machine scaling of the type I-ELM divertor energy flux density to ITER is supported by first principle modelling. ITER relevant disruption experiments and first principle modelling are reported with a set of three disruption mitigation valves mimicking the ITER setup. Insights of the L–H power threshold in Deuterium and Hydrogen are given, stressing the importance of the magnetic configurations and the recent measurements of fine-scale structures in the edge radial electric. Dimensionless scans of the core and pedestal confinement provide new information to elucidate the importance of the first wall material on the fusion performance. H-mode plasmas at ITER triangularity (H  =  1 at βN ~ 1.8 and n/nGW ~ 0.6) have been sustained at 2 MA during 5 s. The ITER neutronics codes have been validated on high performance experiments. Prospects for the coming D–T campaign and 14 MeV neutron calibration strategy are reviewed.

It is recently discussed that a plasma system with drifting ions at near the acoustic phase speed becomes susceptible to weak but finite electron inertial delay effect. In such plasma condition, the linear normal modes of acoustic oscillations undergo resonant linear growth. Such situation exists naturally in transonic zones of boundary plasma layers. The present contribution considers this as a specific case to describe the possible role of an external source driving on the usual ion acoustic soliton solution in the unstable region of the transonic zone assumed to have finite extension. A driven Korteweg-de Vries equation is obtained that is not exactly integrable. It is shown by numerical analysis that the usual acoustic soliton solution exists only for infinitely long wavelength source perturbation. For short wavelength (but within the limit of the long wavelength approximation) source perturbations interesting solutions of single unit of localized oscillatory shock-like structure are obtained. Possible physical interpretations of the results are included in the text.Ã Bharat is an ancient country and is also known as India in recent times.

In this article an interesting result has been reported to highlight the physical implication of finite nonzero electron inertial delay in acoustic oscillations of an ion-beam plasma system. A simple fluid model has been used to demonstrate the excitation of relaxation type resonant instability on the electron inertial delay time scale. Physical arguments have been included to understand and explain the driving mechanism of the instability and its utility to comprehend the ion-beam driven oscillations in plasma sheath experiments. The physical nature and origin of the potential relaxation instability has been correlated to the electron inertial delay effect in the ion current carrying plasma system.