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Experiments on excitation of Alfvén eigenmodes by alpha-particles with bump-on-tail distribution in JET DTE2 plasmas

Harvard Dataverse (Africa Rice Center, Bioversity International, CCAFS, CIAT, IFPRI, IRRI and WorldFish)

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Title Experiments on excitation of Alfvén eigenmodes by alpha-particles with bump-on-tail distribution in JET DTE2 plasmas
 
Identifier https://doi.org/10.7910/DVN/4PTDAC
 
Creator S.E. Sharapov, H.J.C. Oliver, J. Garcia, D.L. Keeling, M. Dreval, V. Goloborodko, Ye.O. Kazakov, V.G. Kiptily, Ž. Štancar, P.J. Bonofiglo, R. Coelho, T. Craciunescu, J. Ferreira, A. Figueiredo, N. Fil, M. Fitzgerald, F. Nabais, M. Nocente, , P.G. Puglia, J. Rivero-Rodriguez, P. Rodrigues, M. Salewski, R.A. Tinguely, L.E. Zakharov, Jet contributors
 
Publisher Harvard Dataverse
 
Description Dedicated experiments were performed in JET DTE2 plasmas for obtaining an α-particle bump-on-tail (BOT) distribution aiming at exciting Alfvén Eigenmodes (AEs). NBI-only heating with modulated power was used so that fusion-born α-particles were the only ions present in the MeV energy range in these DT plasmas. The beam power modulation on a time scale shorter than the α-particle slowing down time was chosen for modulating the α-particle source and thus sustaining a BOT in the α-particle distribution. High-frequency modes in the TAE frequency range and multiple short-lived modes in a wider frequency range have been detected in these DT discharges with interferometry, soft X-ray cameras, and reflectometry. The modes observed were localised close to the magnetic axis, and were not seen in the Mirnov coils. Analysis with the TRANSP and Fokker-Planck FIDIT codes confirms that α-particle distributions with bump-on-tail in energy were achieved during some time intervals in these discharges though no clear correlation was found between the times of the high-frequency mode excitation and the BOT time intervals. The combined MHD and kinetic modelling studies show that the high-frequency mode in the TAE frequency range is best fitted with a TAE of toroidal mode number n= 9. This mode is driven mostly by the on-axis beam ions while the smaller drive due to the pressure gradient of α-particles allows overcoming the marginal stability and exciting the mode [H.J.C. Oliver et al. Toroidal Alfvén eigenmodes observed in low power JET deuterium-tritium plasmas, to be submitted to Nuclear Fusion (2023)]. The observed multiple short-lived modes in a wider frequency range are identified as the on-axis kinetic Alfvén eigenmodes predicted in [M.N. Rosenbluth, P.H. Rutherford, Phys. Rev. Lett. 34 (1975) 1428].
 
Subject Physics
Alfven eigenmodes
alpha particles
bump-on-tail instabilities
DT
JET
 
Date 2024-02-23