Nonlinear effects caused by intense electromagnetic waves
in an electron-positron-ion plasma
P. K. Shukla,
a)
L. Stenflo,
b)
and R. Fedele
c)
Institut fu
¨
r Theoretische Physik IV, Fakulta
¨
tfu
¨
r Physik und Astronomie, Ruhr-Universita
¨
t Bochum,
D-44780 Bochum, Germany
͑Received 19 August 2002; accepted 14 October 2002͒
It is shown that intense radiation nonlinearly interacts with the acousticlike waves in an
electron-positron-ion plasma at nonrelativistic temperatures. The interaction is governed by the
electromagnetic wave equation including the relativistic electron and positron mass variations and
the density changes associated with the acousticlike waves, and an equation for the latter in the
presence of the radiation pressure. The governing nonlinear equations are analyzed to show the
possibility of a novel modulational instability as well as the formation of light bullets and
solitons. © 2003 American Institute of Physics. ͓DOI: 10.1063/1.1527041͔
In the past, a number of authors,
1–3
have studied the
nonlinear propagation of intense electromagnetic waves in
electron-positron-ion ͑e-p-i͒ plasmas, in laboratory
experiments,
4–6
in the early Universe,
7
in fireballs producing
␥
-ray bursts,
8
and in solar flares.
9
Rizzato
1
analytically in-
vestigated the localization of weakly nonlinear circularly po-
larized electromagnetic ͑CPEM͒ waves in a cold plasma
composed of electrons, positrons, and stationary ions. He and
others
10
found that such a three-component plasma supports
radiation driven humped electrostatic potentials, which can
be used to accelerate charged particles. Berezhiani and
Mahajan
2
explored the possibility of large amplitude soliton-
like electromagnetic solitons involving radiation driven com-
pressional potentials in a cold e-p-i plasma. However, in a
warm e-p-i plasma at nonrelativistic temperatures, one has in
addition the possibility of acousticlike waves
11
in which the
ion mass provides the inertia, while the restoring force
comes from the pressures of the electrons and positrons
which have equal masses but opposite charges. This situation
is different from that of sound waves
12
in relativistically hot
e-p plasmas in which there exists a possibility of modula-
tional instabilities
13,14
of electromagnetic waves due to their
coupling with sound waves which are supported by the iner-
tia of the electron and positron fluids.
In this Brief Communication, we consider the nonlinear
interaction between intense electromagnetic waves and the
acousticlike waves
11
that are reinforced by the ponderomo-
tive force of the electromagnetic waves in an unmagnetized
electron-positron-ion plasma at nonrelativistic temperatures.
Specifically, we point out the possibilities of a novel modu-
lational instability, bullets and solitons associated with the
large amplitude electromagnetic waves including the relativ-
istic electron and positron mass variations as well as the
ponderomotive force driven acousticlike waves. The latter do
not have a counterpart in an e-p plasma.
Let us consider the propagation of a large amplitude
CPEM wave with an electric field EϭE(xˆ ϩiyˆ)exp(iK•R
Ϫi⍀t), where K and ⍀ are the wave vector and wave fre-
quency, respectively, and c is the speed of light in vacuum.
The electromagnetic wave equation in the presence of the
relativistic electron and positron mass variations
15
and the
electron and positron density perturbations are obtained from
“ϫBϭ
4
c
Jϩ
1
c
ץ
t
E, ͑1͒
with
Jϭe
͓͑
n
p0
ϩn
p1
͒
v
p
Ϫ
͑
n
e0
ϩn
e1
͒
v
e
͔
, ͑2͒
Bϭ“ ϫA, ͑3͒
EϭϪ
1
c
ץ
t
A, ͑4͒
and
ץ
t
p
j
ϭq
j
E, ͑5͒
a͒
Also at the Department of Plasma Physics, Umea
˚
University, SE-
90187 Umea
˚
, Sweden and the Center for Interdisciplinary Plasma Science,
Max-Planck Institut fu
¨
r Plasmaphysik und extraterrestrische Physik,
D-85741 Garching, Germany.
b͒
Permanent address: Department of Plasma Physics, Umea
˚
University, SE-
90187 Umea
˚
, Sweden.
c͒
Permanent address: Dipartimento di Scienze Fisiche, Universita Federico
II and INFN, Complesso Universitario di M. S. Angelo, Via Cintia,
I-80126 Napoli, Italy.
PHYSICS OF PLASMAS VOLUME 10, NUMBER 1 JANUARY 2003
BRIEF COMMUNICATIONS
The purpose of this Brief Communications section is to present important research results of more limited scope than regular
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