TY  - JOUR
A1  - Yoon, P. H.
A1  - Lopez, R. A.
A1  - Vafin, Sergei
A1  - Kim, S.
A1  - Schlickeiser, R.
T1  - Spontaneous emission of Alfvenic fluctuations
JF  - Plasma physics and controlled fusion
N2  - Low-frequency fluctuations are pervasively observed in the solar wind. The present paper theoretically calculates the steady state spectra of low-frequency electromagnetic (EM) fluctuations of the Alfvenic type for thermal equilibrium plasma. The analysis is based upon a recently formulated theory of spontaneously emitted EM fluctuations in magnetized thermal plasmas. It is found that the fluctuations in the magnetosonic mode branch is constant, while the kinetic Alfvenic mode spectrum is dependent on a form factor that is a function of perpendicular wave number. Potential applicability of the present work in the wider context of heliospheric research is also discussed.
KW  - spontaneous emission
KW  - kinetic Alfven
KW  - magnetosonic
Y1  - 2017
U6  - https://doi.org/10.1088/1361-6587/aa77c3
SN  - 0741-3335
SN  - 1361-6587
VL  - 59
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Vafin, Sergei
A1  - Riazantseva, M.
A1  - Yoon, P. H.
T1  - Kinetic Features in the Ion Flux Spectrum
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - An interesting feature of solar wind fluctuations is the occasional presence of a well-pronounced peak near the spectral knee. These peaks are well investigated in the context of magnetic field fluctuations in the magnetosheath and they are typically related to kinetic plasma instabilities. Recently, similar peaks were observed in the spectrum of ion flux fluctuations of the solar wind and magnetosheath. In this paper, we propose a simple analytical model to describe such peaks in the ion flux spectrum based on the linear theory of plasma fluctuations. We compare our predictions with a sample observation in the solar wind. For the given observation, the peak requires similar to 10 minutes to grow up to the observed level that agrees with the quasi-linear relaxation time. Moreover, our model well reproduces the form of the measured peak in the ion flux spectrum. The observed lifetime of the peak is about 50 minutes, which is relatively close to the nonlinear Landau damping time of 30-40 minutes. Overall, our model proposes a plausible scenario explaining the observation.
KW  - instabilities
KW  - solar wind
KW  - turbulence
KW  - waves
Y1  - 2017
U6  - https://doi.org/10.3847/1538-4357/aa9519
SN  - 0004-637X
SN  - 1538-4357
VL  - 850
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Vafin, Sergei
A1  - Schlickeiser, R.
A1  - Yoon, P. H.
T1  - AMPLIFICATION OF COLLECTIVE MAGNETIC FLUCTUATIONS IN MAGNETIZED BI-MAXWELLIAN PLASMAS FOR PARALLEL WAVE VECTORS. I. ELECTRON-PROTON PLASMA
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - The general electromagnetic fluctuation theory is a powerful tool to analyze the magnetic fluctuation spectrum of a plasma. Recent works utilizing this theory for a magnetized non-relativistic isotropic Maxwellian electron-proton plasma have demonstrated that the equilibrium ratio of vertical bar delta B vertical bar/B-0 can be as high as 10(-12). This value results from the balance between spontaneous emission of fluctuations and their damping, and it is considerably smaller than the observed value vertical bar delta B vertical bar/B-0 in the solar wind at 1 au, where 10(-3) less than or similar to vertical bar delta B vertical bar/B-0 less than or similar to 10(-1). In the present manuscript, we consider an anisotropic bi-Maxwellian distribution function to investigate the effect of plasma instabilities on the magnetic field fluctuations. We demonstrate that these instabilities strongly amplify the magnetic field fluctuations and provide a sufficient mechanism to explain the observed value of vertical bar delta B vertical bar/B-0 in the solar wind at 1 au.
KW  - instabilities
KW  - magnetic fields
KW  - solar wind
KW  - turbulence
KW  - waves
Y1  - 2016
U6  - https://doi.org/10.3847/0004-637X/829/1/41
SN  - 0004-637X
SN  - 1538-4357
VL  - 829
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  -