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

Journal Article · 12 October 2023 · Nuclear Fusion

DOI: https://doi.org/10.1088/1741-4326/acee10 · OSTI ID:2217308

Sharapov, Sergei E.  ^[1]; Oliver, H. J. C.  ^[1]; Garcia, J.  ^[2]; Keeling, D. L. ^[1]; Dreval, M.  ^[3]; Goloborod’Ko, V. ^[4]; Kazakov, Ye O. ^[5]; Kiptily, V. G.  ^[1]; Štancar, Ž.  ^[1]; Bonofiglo, P. J.  ^[6]; Coelho, R. ^[7]; Craciunescu, T.  ^[8]; Ferreira, J.  ^[7]; Figueiredo, A.  ^[7]; Fil, N. ^[1]; Fitzgerald, M. ^[1]; Nabais, F.  ^[7]; Nocente, M.  ^[9]; Puglia, P. G. ^[10]; Rivero-Rodriguez, J.  ^[1] ; Rodrigues, P.  ^[7]; Salewski, M. ^[11]; Tinguely, R. A.  ^[12]; Zakharov, L. E. ^[13]

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1. UK Atomic Energy Authority (UKAEA), Abingdon (United Kingdom)
2. CEA, IRFM, Saint-Paul-lez-Durance (France)
3. National Academy of Sciences of Ukraine (NASU), Kharkov (Ukraine). National Scientific Centre, Kharkov Institute of Physics and Technology (KIPT)
4. Institute for Nuclear Research, Kiev (Ukraine)
5. Laboratory for Plasma Physics, LPP-ERM/ KMS, TEC Partner, Brussels (Belgium)
6. Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)
7. Universidade de Lisboa (Portugal)
8. National Institute for Laser, Plasma and Radiation Physics, Bucharest (Romania)
9. Universit`a di Milano-Bicocca (Italy); National Research Council, Milan (Italy)
10. Ecole Polytechnique Federale Lausanne (EPFL) (Switzerland)
11. Technical University of Denmark, Lyngby (Denmark)
12. Massachusetts Institute of Technology (MIT), Cambridge, MA (United States). Plasma Science and Fusion Center
13. Helsinki University (Finland)

Dedicated experiments were performed in JET DTE2 plasmas for obtaining an α-particle bump-on-tail (BOT) distribution aiming at exciting Alfvén eigenmodes (AEs). Neutral beam injection-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 toroidicity-induced Alfven eigenmode (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 BOT 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 magneto-hydrodynamic (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. The observed multiple short-lived modes in a wider frequency range are identified as the on-axis kinetic AEs predicted in Rosenbluth and Rutherford.

• Research Organization: Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)
• Sponsoring Organization: USDOE
• Contributing Organization: JET Contributors
• Grant/Contract Number: AC02-09CH11466
• OSTI ID: 2217308
• Journal Information: Nuclear Fusion, Vol. 63, Issue 11; ISSN 0029-5515
• Publisher: IOP ScienceCopyright Statement
• Country of Publication: United States
• Language: English