On The Nature Of Kinetic Electrostatic Electron Nonlinear (KEEN) Waves
Authors: I.Y. Dodin and N.J. Fisch
Abstract:
An analytical theory is proposed for the kinetic electrostatic electron nonlinear (KEEN) waves
originally found in simulations by Afeyan et al [arXiv:1210.8105]. We suggest that KEEN waves
represent saturated states of the negative mass instability (NMI) reported recently by Dodin et al
[Phys. Rev. Lett. 110, 215006 (2013)]. Due to the NMI, trapped electrons form macroparticles that
produce eld oscillations at harmonics of the bounce frequency. At large enough amplitudes, these
harmonics can phase-lock to the main wave and form stable nonlinear dissipationless structures that
are nonstationary but otherwise similar to Bernstein-Greene-Kruskal modes. The theory explains
why the formation of KEEN modes is sensitive to the excitation scenario and yields estimates that
agree with the numerical results of Afeyan et al. A new type of KEEN wave may be possible at
even larger amplitudes of the driving eld than those used in simulations so far.
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Submitted to: Physics of Plasmas (October 2013)
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