Nonlinear Excitation of Subcritical Instabilities in a Toroidal Plasma

M. Lesur, K. Itoh, T. Ido, M. Osakabe, K. Ogawa, A. Shimizu, Makoto Sasaki, K. Ida, Inagaki Shigeru, Sanae Itoh

Research output: Contribution to journalArticle

19 Citations (Scopus)

Abstract

In a collisionless plasma, it is known that linearly stable modes can be destabilized (subcritically) by the presence of structures in phase space. However, nonlinear growth requires the presence of a seed structure with a relatively large threshold in amplitude. We demonstrate that, in the presence of another, linearly unstable (supercritical) mode, wave-wave coupling can provide a seed, which is significantly below the threshold, but can still grow by (and only by) the collaboration of fluid and kinetic nonlinearities. By modeling the subcritical mode kinetically, and the impact of the supercritical mode by simple wave-wave coupling equations, it is shown that this new kind of subcritical instability can be triggered, even when the frequency of the supercritical mode is rapidly sweeping. The model is applied to the bursty onset of geodesic acoustic modes in a LHD experiment. The model recovers several key features such as relative amplitude, time scales, and phase relations. It suggests that the strongest bursts are subcritical instabilities, driven by this mechanism of combined fluid and kinetic nonlinearities.

Original languageEnglish
Article numbere015003
JournalPhysical Review Letters
Volume116
Issue number1
DOIs
Publication statusPublished - Jan 8 2016

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toroidal plasmas
excitation
seeds
nonlinearity
collisionless plasmas
thresholds
fluids
kinetics
bursts
acoustics

All Science Journal Classification (ASJC) codes

  • Physics and Astronomy(all)

Cite this

Lesur, M., Itoh, K., Ido, T., Osakabe, M., Ogawa, K., Shimizu, A., ... Itoh, S. (2016). Nonlinear Excitation of Subcritical Instabilities in a Toroidal Plasma. Physical Review Letters, 116(1), [e015003]. https://doi.org/10.1103/PhysRevLett.116.015003

Nonlinear Excitation of Subcritical Instabilities in a Toroidal Plasma. / Lesur, M.; Itoh, K.; Ido, T.; Osakabe, M.; Ogawa, K.; Shimizu, A.; Sasaki, Makoto; Ida, K.; Shigeru, Inagaki; Itoh, Sanae.

In: Physical Review Letters, Vol. 116, No. 1, e015003, 08.01.2016.

Research output: Contribution to journalArticle

Lesur, M, Itoh, K, Ido, T, Osakabe, M, Ogawa, K, Shimizu, A, Sasaki, M, Ida, K, Shigeru, I & Itoh, S 2016, 'Nonlinear Excitation of Subcritical Instabilities in a Toroidal Plasma', Physical Review Letters, vol. 116, no. 1, e015003. https://doi.org/10.1103/PhysRevLett.116.015003
Lesur M, Itoh K, Ido T, Osakabe M, Ogawa K, Shimizu A et al. Nonlinear Excitation of Subcritical Instabilities in a Toroidal Plasma. Physical Review Letters. 2016 Jan 8;116(1). e015003. https://doi.org/10.1103/PhysRevLett.116.015003
Lesur, M. ; Itoh, K. ; Ido, T. ; Osakabe, M. ; Ogawa, K. ; Shimizu, A. ; Sasaki, Makoto ; Ida, K. ; Shigeru, Inagaki ; Itoh, Sanae. / Nonlinear Excitation of Subcritical Instabilities in a Toroidal Plasma. In: Physical Review Letters. 2016 ; Vol. 116, No. 1.
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