Nonlinear beat wave decay of Kelvin/diocotron waves on a two-dimensional vortex

Physics of Fluids · 2024-03-01 · 4 citations

We describe theory and experiments investigating nonlinear beat wave decay of diocotron modes on a nonneutral plasma column (or Kelvin waves on a vortex). Specifically, a Kelvin/diocotron pump wave varying as Ap exp [i(lpθ−ωpt)] decays into two waves: a Kelvin/diocotron daughter wave with exponentially growing amplitude Ad(t), mode number ld<lp, and frequency ωd; and an exponentially growing “beat wave” with mode number lb and frequency ωb. Nonlinear wave–wave coupling requires lb=lp−ld and ωb=ωp−ωd. The new theory simplifies and extends a previous weak-turbulence theory for the exponential growth rate of this instability, by instead using an eigenmode expansion to describe the beat wave as a wavepacket of continuum (Case/van Kampen) modes. The new theory predicts the growth rate, the nonlinear frequency shift (both proportional to Ap2), and the functional form of the beat wave, with amplitude proportional to ApAd*(t). Experiments observe beat wave decay on electron plasma columns for a range of mode numbers up to lp=5 and ld = 4, with results in quantitative agreement with the theory, including the ld = 1 case for which measured growth rates are negligible, as expected theoretically.

The electric fields and “lightning jets” of the Sun and solar wind

Physics of Plasmas · 2023-10-01 · 1 citations

A model of electric energization of the solar wind and corona is developed, including electro-magnetic particle effects precluded by traditional magneto-hydro (MHD) assumptions. Using standard 1D radial solar models for particle density and temperature, the core gravito-electric field is calculated; and the range of possible photospheric photo-electric fields is estimated. The extant DC field apparently arises from about 460 C of charge displacement, mainly caused by the immense solar energy flux pushing electrons outward. Energetically, this electric field can accelerate surface protons out of the 2 keV gravity well and up to the 4 keV energies observed in the fast solar wind. The electrical energy is released in pervasive, persistent “proton lightning jets,” which are proton beams, charge-neutralized by co-propagating electrons. The jets are formed by pinched “avalanche breakdown” of the weakly ionized photosphere, probably initiated on the down-welling edges of solar surface granulations. These energetic jets will glow as discrete filamentary surface spicules and will be observed in reflected solar light as the diffuse K-corona. Significantly, the total charge displacement and observed fast wind speed are quantitatively predicted by a novel “virial limit”: the (positive) electrical potential energy at r = 0 is limited in magnitude to the 10 keV gravitational well at r = 0.

The Electric Fields and "Lightning Jets" of the Sun and Solar Wind

arXiv (Cornell University) · 2023-05-22

A model of electric energization of the Solar Wind and Corona is developed, including electro-magnetic (EM) particle effects precluded by traditional magneto-hydro (MHD) assumptions. Using standard 1-D radial Solar models for particle density and temperature, the Core gravito-electric field is calculated; and the range of possible Photospheric photoelectric fields is estimated. The extant DC field apparently arises from about 460.Coulombs of charge displacement, mainly caused by the immense Solar energy flux pushing electrons outward. Energetically, this electric field can accelerate surface protons out of the 2.keV gravity well and up to the 4. keV energies observed in the Fast Solar Wind. The electrical energy is released in pervasive, persistent "proton lightning jets", which are proton beams, charge-neutralized by co-propagating electrons. The jets are formed by pinched "avalanche breakdown" of the weakly ionized Photosphere, probably initiated on the down-welling edges of Solar surface granulations. These energetic jets will glow as discrete filamentary surface spicules, and will be observed in reflect solar light as the diffuse K-Corona. Significantly, the total charge displacement and observed Fast Wind Speed (FWS) are quantitatively predicted by a novel "virial limit": the (positive) electrical potential energy at r=0 is limited in magnitude to the 10.keV gravitational well at r=0.

Electric Fields, Currents, and Magnetic Fluctuations of the Photosphere and Solar Wind

AGU Fall Meeting Abstracts · 2020-12-01

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TG waves in θ-asymmetric magnetized plasma column

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