Electrostatic waves in streaming magnetized plasma: Linearly independent
polarized modes
Antaryami Naik
Department of Physics, Swami Vivekananda Memorial College, Jagatsinghpur, Orissa, India
J. N. Mohanty
a)
Centre of Astrophysics, Plot No. 438, Nuasahi, Nayapally, Bhubaneswar, Orissa, India
͑Received 5 May 2000; accepted 17 October 2000͒
The evolution of two linearly independent polarized modes due to transverse propagation of
electrostatic waves in a two-component streaming magnetic plasma is analytically studied. The
modified frequency spectra reveal that the refractive index and amplification factor markedly
increase with the rise in thermal energy, especially in strong magnetic-field lines (B
0
ϳ10
3
kG).
However, with the increase in streaming velocity, the refractive index sharply diminishes. In weak
magnetic-field lines (B
0
ϳ10
Ϫ2
kG), the refractive index decays with the increase in thermal
energy, whereas the amplification shows an increasing trend. © 2001 American Institute of
Physics. ͓DOI: 10.1063/1.1332120͔
I. INTRODUCTION
The study of streaming anisotropic plasmas in an exter-
nal magnetic field is of potential use when the plasma is
driven by a beam. Such beam-driven or transient plasmas are
encountered in nature, such as cosmic rays, Alfve
´
n waves,
Whistlers, interstellar jets, magnetospheric space, and astro-
physical plasmas. The plasma is a typical dynamical medium
having a large number of degrees of freedom, and streaming
or plasma mass motion is a concomitant and intrinsic feature
in natural plasmas. It presents many new and interesting phe-
nomena like polarized wave modes, etc., particularly in the
beam-plasmas of the solar wind, solar storm, streams of
coronal discharges, jets, shock waves, etc. These inherent
beam-plasma motions and features are equally studied in
laboratory diagnostics and experimental space plasma simu-
lations with plasma expansion across magnetic-field lines.
In view of the above potential applications, waves and
instabilities were recently studied with regard to streaming
magnetized plasmas,
1
especially when the propagation is ar-
bitrary and aligned to the magnetic-field lines. The impact of
beam motion or streaming mechanism in natural plasmas is
analytically elucidated there, and the propagation of waves
and instabilities pertaining to cold and warm plasma environ-
ments. Early works on linearized approximations also con-
tain streaming with anisotropy in particle distribution
function
2
in a relativistic plasma that equally includes waves
in different thermal regimes having dispersion and damping
analysis. In a similar context, diffusion aspects
3,4
in a poten-
tial field have been covered that included streaming or beam-
motion. But the streaming aspect has not yet been fully re-
solved. Recently, cross-field diffusion in nonrelativistic
5
regimes of temperature with streaming transport aspect have
been performed and specific transport coefficients were de-
rived. Propagation and absorption of ordinary waves in a
fully relativistic plasma have been dealt with, both for
transverse
6
and arbitrary
7
angles of wave propagation to the
magnetic field, but no streaming features have been covered.
Both dispersion and numerical profiles of the refractive in-
dex vs
p
2
/
2
, density vs temperature have been analyzed in
their study.
6,7
With regard to experimental analysis of laser
plasma expansion and collimation across magnetic-field
lines
8
(Bϭ0to10kG͒, transverse velocity shear-driven in-
stabilities in linear regimes have been covered. Along the
same line, highly collimated plasma jets
9
have been pro-
duced with laser irradiation of solid barium targets, and the
expansion of plasma has been discussed, both across (
ϭ
/2) and along (
ϭ0°) a strong magnetic field where
flute-like striations with electron–ion hybrid velocity shear
instability are visible. On the other hand, propagation of neu-
tralized plasma beams
10
across a transverse magnetic field
have been studied by a combination of single particle and
collective plasma processes for low- and high-density plas-
mas in a high-

regime. It is shown that the beam plasma
magnetization and transport processes occur in large ion gy-
roradius beams, which are dominated by ion motion with
limiting conditions y/
i
Ͻ1or
pj
/⍀
j
Ͼ1 and y/
i
Ͼ1or
pj
/⍀
j
Ͻ1. Note that y and
i
correspond to length scale
and
pj
corresponds to time scale (
ϭ2
/
pj
).
In general, the transverse propagation of electrostatic
waves present many new and interesting physical scenarios
especially in nonrelativistic temperature regimes (KT
Ͻ1 keV) in the presence of a beam. The electrons and ions
become relativistic at temperature 10
8
K and 10
13
K, re-
spectively, and the interesting wave modes, streaming cyclo-
tron dispersions, etc., below these threshold temperatures are
addressed in this study of magnetoplasma. The goal of this
paper is to uncover the polarization field aspects bearing on
streaming dispersion relations ͑wave number frequency rela-
tion͒ of plasma species, especially when plasma flows across
the magnetic-field lines ͑transverse mode͒. Specifically, it
reveals two linearly independent polarized modes and intrin-
a͒
Electronic mail: jn_mohanty@hotmail.com
PHYSICS OF PLASMAS VOLUME 8, NUMBER 3 MARCH 2001
7261070-664X/2001/8(3)/726/8/$18.00 © 2001 American Institute of Physics