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Efficient generation of energetic ions in multi-ion plasmas by radio-frequency heating

Abstract

We describe a new technique for the efficient generation of high-energy ions with electromagnetic ion cyclotron waves in multi-ion plasmas. The discussed ‘three-ion’ scenarios are especially suited for strong wave absorption by a very low number of resonant ions. To observe this effect, the plasma composition has to be properly adjusted, as prescribed by theory. We demonstrate the potential of the method on the world-largest plasma magnetic confinement device, JET (Joint European Torus, Culham, UK), and the high-magnetic-field tokamak Alcator C-Mod (Cambridge, USA). The obtained results demonstrate efficient acceleration of 3He ions to high energies in dedicated hydrogen–deuterium mixtures. Simultaneously, effective plasma heating is observed, as a result of the slowing-down of the fast 3He ions. The developed technique is not only limited to laboratory plasmas, but can also be applied to explain observations of energetic ions in space-plasma environments, in particular, 3He-rich solar flares.

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Figure 1: A new technique for fast-ion generation in magnetized multi-ion plasmas.
Figure 2: Illustration of the performance of the D–(3He)–H three-ion ICRH scenario on Alcator C-Mod and JET tokamaks.
Figure 3: Gamma-ray emission from 3He + 9Be nuclear reactions, proving the presence of energetic ICRH-accelerated 3He ions.
Figure 4: Excitation of Alfvénic eigenmodes in magnetic fluctuation spectrograms, another proof of the presence of ICRH-accelerated fast ions.
Figure 5: Three-ion ICRH scenarios also explain some of the observations of energetic ions in space environments, in particular, 3He-rich solar flares.

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Acknowledgements

This paper is dedicated to the late P. E. M. Vandenplas, founder and first director of LPP-ERM/KMS, in recognition of his lifelong outstanding commitment to fusion research, in particular to ICRH. The support from the JET and Alcator C-Mod Teams is warmly acknowledged. We are grateful to A. Cardinali, C. Castaldo, R. Dumont, J. Eriksson, T. Fülöp, C. Giroud, C. Hellesen, S. Menmuir and M. Schneider for fruitful discussions. 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 under grant agreement no. 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. This work was also supported by the US DoE, Office of Science, Office of Fusion Energy Sciences, SciDAC Center for Simulation of Wave Plasma Interactions under DE-FC02-01ER54648 and the User Facility Alcator C-Mod under DE-FC02-99ER54512. The Alcator C-Mod Team author list is reproduced from ref. 12. The JET Contributors author list is reproduced from ref. 33.

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All authors have contributed to the publication, being variously involved in the design of the experiments, in running the diagnostics, acquiring data and finally analysing the processed data.

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Correspondence to Ye. O. Kazakov.

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Kazakov, Y., Ongena, J., Wright, J. et al. Efficient generation of energetic ions in multi-ion plasmas by radio-frequency heating. Nature Phys 13, 973–978 (2017). https://doi.org/10.1038/nphys4167

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