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STEADY-STATE MODEL OF SOLAR WIND ELECTRONS REVISITED
Yoon, Peter H.,Kim, Sunjung,Choe, G. S. IOP Publishing 2015 The Astrophysical journal Vol.812 No.2
<P>In a recent paper, Kim et al. put forth a steady-state model for the solar wind electrons. The model assumed local equilibrium between the halo electrons, characterized by an intermediate energy range, and the whistler-range fluctuations. The basic wave-particle interaction is assumed to be the cyclotron resonance. Similarly, it was assumed that a dynamical steady. state is established between the highly energetic superhalo electrons and high-frequency Langmuir fluctuations. Comparisons with the measured solar wind electron velocity distribution function (VDF) during quiet times were also made, and reasonable agreements were obtained. In such a model, however, only the steady-state solution for the Fokker-Planck type of electron particle kinetic equation was considered. The present paper complements the previous analysis by considering both the steady-state particle and wave kinetic equations. It is shown that the model halo and. superhalo electron VDFs, as well as the assumed wave intensity spectra for the whistler and Langmuir fluctuations, approximately satisfy the quasi-linear wave kinetic equations in an approximate sense, thus further validating the local equilibrium model constructed in the paper by Kim et al.</P>
Oblique nonlinear whistler wave
Yoon, Peter H.,Pandey, Vinay S.,Lee, Dong-Hun American Geophysical Union 2014 JOURNAL OF GEOPHYSICAL RESEARCH. SPACE PHYSICS Vol.119 No.3
Motivated by satellite observation of large-amplitude whistler waves propagating in oblique directions with respect to the ambient magnetic field, a recent letter discusses the physics of large-amplitude whistler waves and relativistic electron acceleration. One of the conclusions of that letter is that oblique whistler waves will eventually undergo nonlinear steepening regardless of the amplitude. The present paper reexamines this claim and finds that the steepening associated with the density perturbation almost never occurs, unless whistler waves have sufficiently high amplitude and propagate sufficiently close to the resonance cone angle.
YOON, PETER H.,SEOUGH, JUNG JOON,KIM, KHAN HYUK,LEE, DONG HUN Cambridge University Press 2012 Journal of plasma physics Vol.78 No.1
<B>Abstract</B><P>In the present paper, quasilinear development of anisotropy-driven electromagnetic instabilities is computed on the basis of recently formulated empirical wave dispersion relation and compared against exact numerical calculation based upon transcendental plasma dispersion function and exact numerical roots. Upon comparison with the exact method it is demonstrated that the empirical model provides reasonable results. The present findings may be relevant to space physical application, as the present paper provides a useful short-cut research method for self-consistent analysis of temporal development of anisotropy-driven instabilities.</P>
Self-Consistent Generation of Superthermal Electrons by Beam-Plasma Interaction
Yoon, Peter H.,Rhee, Tongnyeol,Ryu, Chang-Mo American Physical Society 2005 Physical Review Letters Vol.95 No.21
<P>It has been known since the early days of plasma physics research that superthermal electrons are generated during beam-plasma laboratory experiments. Superthermal electrons (the kappa distribution) are also ubiquitously observed in space. To explain such a feature, various particle acceleration mechanisms have been proposed. However, self-consistent acceleration of electrons in the context of plasma kinetic theory has not been demonstrated to date. This Letter reports such a demonstration. It is shown that the collisionality, defined via the 'plasma parameter' g=1/n(lambda(D)(3), plays a pivotal role. It is found that a small but moderately finite value of is necessary for the superthermal tail to be generated, implying that purely collisionless (g=0) Vlasov theory cannot produce a superthermal population.</P>