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Enhanced performance in fusion plasmas through turbulence suppression by megaelectronvolt ions

Abstract

Alpha particles with energies on the order of megaelectronvolts will be the main source of plasma heating in future magnetic confinement fusion reactors. Instead of heating fuel ions, most of the energy of alpha particles is transferred to electrons in the plasma. Furthermore, alpha particles can also excite Alfvénic instabilities, which were previously considered to be detrimental to the performance of the fusion device. Here we report improved thermal ion confinement in the presence of megaelectronvolts ions and strong fast ion-driven Alfvénic instabilities in recent experiments on the Joint European Torus. Detailed transport analysis of these experiments reveals turbulence suppression through a complex multi-scale mechanism that generates large-scale zonal flows. This holds promise for more economical operation of fusion reactors with dominant alpha particle heating and ultimately cheaper fusion electricity.

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Fig. 1: Schematic view of the tokamak geometry.
Fig. 2: Improved thermal ion confinement in fusion plasmas with MeV ions and unstable TAEs.
Fig. 3: Thermal ion transport suppression in plasmas with MeV ions and fast-ion-driven modes.
Fig. 4: Evidence for the nonlinear generation of zonal structures.

Data availability

The JET experimental data are stored in the Processed Pulse File system, which is a centralized data storage and retrieval system for data derived from raw measurements within the JET torus, and from other sources such as simulation programs. These data are fully available for EUROfusion Consortium members and can be accessed by non-members under request to EUROfusion. Numerical data that support the outcome of this study are available from the corresponding authors upon reasonable request.

Code availability

The research codes cited in the paper require prior detailed knowledge of the implemented physics models and are under continuous development. The corresponding authors can be contacted for any further information.

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Acknowledgements

We thank M. Baruzzo and F. Nave for the preparation and execution of JET experiments discussed in this paper; E. de la Luna for support in detailing the experimental diagnostics of JET; A. Ho for assistance in processing the experimental data; T. Görler for providing essential advice to ensure the correct numerical setup for the GENE modelling reported in this paper; Y. Camenen, X. Garbet and A. Bierwage for fruitful discussions about the gyrokinetic analyses; G. Giruzzi for valuable suggestions on the article strategy. The simulations were performed on the IRENE Joliot-Curie HPC system, in the framework of the PRACE projects IONFAST and AFIETC, led by J. Garcia, and on the CINECA Marconi HPC within the project GENE4EP, led by D. Zarzoso. This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 and 2019-2020 under grant agreement no. 633053. The views and opinions express herein do not necessarily reflect those of the European Commission. Part of the work by Ye. O. Kazakov and J.Ongena was also carried out in the framework of projects done for the ITER Scientist Fellow Network (ISFN).

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The reported JET experiments were designed and coordinated by Ye. O. Kazakov, M. Nocente, J. Garcia and J. Ongena; S. Mazzi, J. Garcia, D. Zarzoso and S. Benkadda performed gyrokinetic modelling and subsequent analysis, including additional simulations requested by the reviewers. Input data for gyrokinetic modelling were provided by Ž. Štancar, G. Szepesi and M. Dreval. Ž. Štancar performed TRANSP modelling. J. Garcia performed power balance analysis and CRONOS simulations. M. Dreval provided analysis of the TAE radial location and the correlation reflectometer data. The bispectral analyses were performed by S. Mazzi and D. Zarzoso, J. Eriksson and A. Sahlberg provided neutron measurements data from TOFOR. The original manuscript was written by S. Mazzi, J. Garcia, D. Zarzoso, Ye. O. Kazakov and J. Ongena with feedback from all the authors. Major revisions of this manuscript were undertaken by Ye. O. Kazakov, J. Ongena, J. Garcia and S. Mazzi.

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Correspondence to S. Mazzi or J. Garcia.

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Nature Physics thanks Neal Crocker, Chris Holland and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Mazzi, S., Garcia, J., Zarzoso, D. et al. Enhanced performance in fusion plasmas through turbulence suppression by megaelectronvolt ions. Nat. Phys. 18, 776–782 (2022). https://doi.org/10.1038/s41567-022-01626-8

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