Control of wave interaction processes in plasma
The results of processes investigation of nonlinear interaction of wave in plasma were expounded. First of all the mechanisms of the processes control of three frequencies wave interaction were considered. It was shown that using of the whirligig principle allows to point out to conditions of existe...
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nasplib_isofts_kiev_ua-123456789-1954232025-02-23T17:30:28Z Control of wave interaction processes in plasma Керування процесами взаємодії хвиль у плазмі Управление процессами взаимодействия волн в плазме Buts, V.O. Kovalchuk, I.K. Tolstoluzhsky, O.P. Zagorodny, A.G. Nonlinear processes The results of processes investigation of nonlinear interaction of wave in plasma were expounded. First of all the mechanisms of the processes control of three frequencies wave interaction were considered. It was shown that using of the whirligig principle allows to point out to conditions of existence of decay processes and to conditions of suppression of decay processes. It was discovered that separated waves with circle polarization do not decay in plasma. Викладені результати дослідження процесів нелінійної взаємодії хвиль у плазмі. Насамперед розглянуті механізми керування процесами тричастотної взаємодії. Показано, що використання принципу дзиґи дозволяє вказати на умови існування розпадних процесів і на умови придушення процесів розпаду. Виявлено, що окремі хвилі із круговою поляризацією не розпадаються в плазмі. Изложены результаты исследования процессов нелинейного взаимодействия волн в плазме. Прежде всего рассмотрены механизмы управления процессами трехчастотного взаимодействия. Показано, что использование принципa юлы позволяет указать на условия существования распадных процессов и на условия подавления процессов распада. Обнаружено, что отдельные волны с круговой поляризацией не распадаются в плазме. This work was partially supported by the Target Program “Physics of Plasmas and Plasma Electronics: fundamentals and applications” of the National Academy of Sciences of Ukraine (Grant No. 0117U006867). 2021 Article Control of wave interaction processes in plasma / V.O. Buts, I.K. Kovalchuk, O.P. Tolstoluzhsky, A.G. Zagorodny // Problems of Atomic Science and Technology. — 2021. — № 4. — С. 144-148. — Бібліогр.: 5 назв. — англ. 1562-6016 PACS: 52.35.Mw DOI: https://doi.org/10.46813/2021-134-144 https://nasplib.isofts.kiev.ua/handle/123456789/195423 en Вопросы атомной науки и техники application/pdf Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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Nonlinear processes Nonlinear processes Buts, V.O. Kovalchuk, I.K. Tolstoluzhsky, O.P. Zagorodny, A.G. Control of wave interaction processes in plasma Вопросы атомной науки и техники |
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The results of processes investigation of nonlinear interaction of wave in plasma were expounded. First of all the mechanisms of the processes control of three frequencies wave interaction were considered. It was shown that using of the whirligig principle allows to point out to conditions of existence of decay processes and to conditions of suppression of decay processes. It was discovered that separated waves with circle polarization do not decay in plasma. |
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Article |
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Buts, V.O. Kovalchuk, I.K. Tolstoluzhsky, O.P. Zagorodny, A.G. |
| author_facet |
Buts, V.O. Kovalchuk, I.K. Tolstoluzhsky, O.P. Zagorodny, A.G. |
| author_sort |
Buts, V.O. |
| title |
Control of wave interaction processes in plasma |
| title_short |
Control of wave interaction processes in plasma |
| title_full |
Control of wave interaction processes in plasma |
| title_fullStr |
Control of wave interaction processes in plasma |
| title_full_unstemmed |
Control of wave interaction processes in plasma |
| title_sort |
control of wave interaction processes in plasma |
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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Nonlinear processes |
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Control of wave interaction processes in plasma / V.O. Buts, I.K. Kovalchuk, O.P. Tolstoluzhsky, A.G. Zagorodny // Problems of Atomic Science and Technology. — 2021. — № 4. — С. 144-148. — Бібліогр.: 5 назв. — англ. |
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ISSN 1562-6016. ВАНТ. 2021. № 4(134) 144
https://doi.org/10.46813/2021-134-144
CONTROL OF WAVE INTERACTION PROCESSES IN PLASMA
V.O. Buts
2,3
, I.K. Kovalchuk
2
, O.P. Tolstoluzhsky
2
, A.G. Zagorodny
1
1
Bogolyubov Institute for Theoretical Physics, National Academy of Sciences of Ukraine,
Kyiv, Ukraine;
2
National Science Center “Kharkov Institute of Physics and Technology”, Kharkiv, Ukraine;
3
Institute of Radio Astronomy of NAS of Ukraine, Kharkiv, Ukraine
E-mail: vbuts@kipt.kharkov.ua
The results of processes investigation of nonlinear interaction of wave in plasma were expounded. First of all the
mechanisms of the processes control of three frequencies wave interaction were considered. It was shown that using
of the whirligig principle allows to point out to conditions of existence of decay processes and to conditions of sup-
pression of decay processes. It was discovered that separated waves with circle polarization do not decay in plasma.
PACS: 52.35.Mw
INTRODUCTION
Processes in plasma are separated into two funda-
mental directions: processes of interaction wave-particle
type and one of wave-wave type. In the last case pro-
cesses of wave interaction can be divided on parametric
processes and nonlinear ones. Processes of three wave
interaction in plasma should be highlighted from non-
linear ones. These processes are mostly studied and
most often appear in experiment. Such feature of these
interactions is connected that they are conditioned by
the quadratic nonlinearity. The nonlinearities of more
higher order do not observe in experiment (they are
small and proportional to third and more higher power
of small parameters). Essential meaning among three
wave interaction in plasma have decays. They allow to
transform energy of high frequency waves into energy
of low frequency ones that effectively heat plasma. This
is positive function of decays. On other hand they can
prevent to propagation and accumulation wave energy
in the plasma waveguides and cavities. Such to effec-
tively to control the characteristics of interacting waves
it is necessary to know conditions that will support de-
cays and that will support these processes. In this work
the answers for some of these questions will be present-
ed. The principle of whirligig was putted into base of
finding of effective mechanism for control of wave in-
teraction processes in plasma [1, 2].
1. STABILIZATION OF THREE WAVE
DECAY PROCESS IN PLASMA
As example of using of whirligig principle let us
consider stabilization of well studied (see, for example,
[3,4]) three wave process in plasma. The set of equa-
tions that describes investigating processes will look
like this
0 0 1 2A A A ; 1 1 0 2A A A ; 2 2 0 1 3A A A A ; 3 2A A . (1)
Here 0A – amplitude of wave that decays, with max-
ima frequency 0 ; 1A amplitude of high frequency
wave, on that take place decay. The frequency of this
wave equals 1 ; 2A – amplitude of low frequency wave
that take part in the process of three wave deacay. The
frequency of this wave equals . There is synchronism
between waves ( 0 1 ). 3A – amplitude of fourth
wave that as we suppose must suppress decay process.
This wave have frequency that equals to one of low fre-
quency wave and is synchronous with them and interac-
tion with them with coefficient that equals .
We will to study the initial study of decay. In this
case amplitude of decaying wave can be considered as
constant ( 0A const ). Then equation for amplitude 2A
is obtained from set of equation (1):
22
2 1 2 0 2 0A A A
. (2)
From equation (2) it is seen that decay process will
be suppressed if following condition will be satisfied:
22
1 2 0A . (3)
Taking into account, that first addend in square
brackets is conditioned by the linear process and second
is conditioned by nonlinear process then inequality is
satisfied easily.
Inequality (3) was obtained by using additional sta-
bilizing perturbance ( 3A ). The whirligig principle may
be us full to find out conditions of conditions decay ex-
istence and to find out conditions of suppression. As
example of such analysis we will consider processes of
nonlinear three wave interaction in the Magnetoactive
plasma.
1.1. FORMULATION OF PROBLEM.
MAIN EQUATION
Common initial equations are Maxwell ones for
field, continuity equation for plasma density and equa-
tion of motion for plasma particles:
1 4 1
, , ,
0, .
E H
rot H j rot E j env
c t c c t
n v e e
nv v v E vH
t t m mc
(4)
To avoid of unwieldy formulae, physical content of
which is difficultly to understand, we in this section
limit our consideration by one dimensional case, i.e. the
derivatives that do not equals zero are temporal one and
one of the space derivative: 0 and 0
z t
.
Components of field we select in the form:
x yE ,H ; y xE ,H high frequency HF field,
mailto:vbuts@kipt.kharkov.ua
ISSN 1562-6016. ВАНТ. 2021. № 4(134) 145
zE longitudinal low frequency LF field, (5)
and also
0 zH H const – constant external magnetic
field in which plasma is placed
In the magnetoactive plasma natural modes are
waves with circular polarization. Keep in mind this we
introduce new dependent variables:
; ;x y x y x yE E iE H H iH v v iv . (6)
Set of equations (4) for this new dependent variables
is transformed into next one:
1 1
( ) ,
4
,
( ) ( ).
y x
z H z
E
H iH i H
z c t c t
H i en
E i v
z c t c
e e
v v v E i v i v H
t z m mc
(7)
where 0 /H eH mc electron cyclotron frequency.
If dependent variables from coordinate z is as
( ~ ikze ), equations (7) are ones for two nonlinear, con-
nected oscillators for two HF waves:
22 2
0 0
2 2 2 2 2
01
2 2
4 41
44
H
H z
e n enE E
E i v
z c t mc c
enen ve
E i v v iH
c m c z
(8)
( ) ( )z H z
e e
v v v E i v i v H
t z m mc
.(9)
Here 2
04 /p e n m is plasma frequency which is
frequency of excited LF-wave.
Dispersion curves for electromagnetic and plasma
waves is presented on Figs. 1, 2. Arrows point out pos-
sible resonantly interacting triplets of wave.
Fig. 1. Dispersion
diagram of wave that
propagate in one direction
Fig. 2. Dispersion diagram
of wave that propagate
different directions
Latter we will neglect by dependence from space
coordinate (resonator case). In this case all dependence
versus coordinate can be rewrited as /G z ikG for
high frequence variables, and /G z i G for low
frequency ones. In this case set of equations for low
frequency variables has the form:
1
0( )z
n
i v n n
t
. (10)
24
2
z
z
v e e e kc
n i v v E v E
t i m mc
.(11)
In the nonlinear addend of set (10), (11) it may sub-
stitute expressions that obtained from linear equations.
Solution of equations (8), (9) we will find in the
form:
( )exp( ) . . , 1,2,3j j jE A t i k c j . (12)
Here j j jt k z ;
j and
jk frequency and
wave vector of interacting wave. These wave character-
istic satisfy to linear dispersion equation. Amplitudes
( )jA t slowly vary as a result of nonlinear wave interac-
tion. Frequencies and wave vectors of interacting waves
must satisfy to famous synchronism conditions:
1 2 3 , 1 2 3k k k . (13)
1.2. DECAY OF TYPE t t l TRANSVERCE
WAVE WITHOUT EXTERNAL MAGNETIC
FIELD 0H
First of all we will consider most simple and well
studied decay of transverse wave into transverse one
and plasma one when external magnetic field is absent
0H . Dispersion diagrams waves are presented on
Figs. 1, 2. This is decay of t t l type. In this case it
may be limited by studying of dynamics of linear polar-
ization wave with components xE , yH 0y xE H .
Then ; ;x x yE E v v H iH .
For analysis of slow nonlinear dynamics of ampli-
tudes of interacting waves from equations (8 - 11) by
usual method [3 - 5] the following set of shorted equa-
tions to defining of these amplitudes is obtained:
1
2 3
22
pA
A a
t
, 2
1 3
12
pA
A a
t
(14)
2
1 23
1 2
1 22
k ka e
A A
t m
.
In this set for slow function of longitudinal velocity
the new designation was introduced:
3 3A a .
The results of this section, in particular integrals,
practically do not differ from results, presented in [3].
1.3. DECAY OF WAVES WITH CIRCULAR
POLARIZATION
Using whirligig principle we expect that in this case
one wave with circular polarization will not decay. De-
cay process will be suppressed.
In this case it is necessary to take into account all
components of electromagnetic waves field. Using set
of equations (8) - (10) it may obtain following set of
shorted equations to define amplitudes jA that slowly
varying and describe dynamics wave amplitudes with
right and left circular polarization:
1
2 3
22
pA
A a
t
, 2
1 3
12
pA
A a
t
, (15)
2
1 23
1 2 1 2
1 24
k ka e
A A A A
t m
.
The most essential results that is seen at analysis of
third equation of set (15) is fact that amplitude of third
wave (low frequency, Langmuir) does not change with
time ( 3a const ) if field of high frequency wave con-
tains only wave with circular polarization. Really from
third equation of set (15) it is seen that multiplier in
square brackets of right part of this equation contains
ISSN 1562-6016. ВАНТ. 2021. № 4(134) 146
only products of amplitudes of different polarization. If
wave field that decaying contains only one polarization,
then factor in square brackets is zero. Thus wave with
circular polarization will not take part in three wave
interaction (in decay of t t l type).
1.4. DECAY OF t t l TYPE
WITH EXTERNAL MAGNETIC FIELD 0H
Let us consider most common case when there are
all components of fields of electromagnetic wave and
plasma is placed in external magnetic field. The shorted
set of equations that describes dynamics of high fre-
quencies transverse wave may be obtained from set (4).
Solution for high frequency wave may find in form:
2
1
( ) exp( ) . .x j j
j
E A t i k c
;
2
1
( ) exp( ) . .y j j
j
E B t i k c
(16)
Then to find dynamics of low frequency waves the
following shorted equation is obtained:
2
1 2
1 2 22 22
1 22
3
2
1 2
1 2 22 2
1 22
H
H
H
H
k i
A A B
ia e
t m
k i
B B A
i
.(17)
It is lightly to show that in this case if in the interac-
tion process takes part only one transverse natural wave
with circular polarization, then such waves do not decay
into transverse and longitudinal ones, i.e. process
t t l can not realize.
To prove this fact enough in formula (17) substitute
expression:
/ 2; / 2x yE E E E E E i . (18)
Then it is lightly to see when there is only one wave
with circular polarization ( E or E ) the right part of
equation (15) (and equation (17) too) is zero. This
means that such transverse wave which rotates on circle
does not excite longitudinal plasma wave and does not
decay.
1.5. INFLUENCE OF FARADEY EFFECT
ON DECFY PROCESS
Above we seen, if in magnetoactive plasma excited
only one natural wave, then process of decay will be
suppressed. Such process of decay is realized only in
that case when in plasma excited two waves with right
and left circular polarization. But from whirligig princi-
ple it follow, if waves rotate enough fast, this may rip
off instability in the magnetoactive plasma wave rotate
because of Faraday effect. This is linear process. This
rotation can suppress process of decay. It may find con-
dition of such suppression. For this it may find follow-
ing shorted equations from equations (7) that describe
dynamics of waves component at Faraday effect
;x y y xE E E E ; (19)
where /E E t ; 2 2 2/ 2H p H .
When formulae were obtained we supposed
1 2 ; ,H p
E i E . (20)
Formula (20) point out on fact that natural modes
take additional phase dynamics that conditioned by Far-
aday effect. This additional dynamics will appear as
detuning of synchronism, for example, in equation (17),
not allowing to excite Langmuir wave. But if amplitude
of decaying will be enough large, this detuning will not
essentially change dynamics of wave interaction. To
define value of this amplitude from equations, for ex-
ample (15), it is possible to find value of increment of
decay instability:
/pc ; /eE mc . (21)
If value of this increment will be larger than detun-
ing, conditioned by Faraday effect then decay process
will be realized. The condition of realization of such
decay is inequalities.
;
3/2
/ /H pc . (22)
2. RESULTS OF NUMERICAL ANALYSIS
The results described above were obtained by ana-
lyzing the shortened equations. Such equations are
much simpler than the original equations. However,
when they were obtained, many terms and many deriva-
tives were discarded. The question arises: to what extent
do the results obtained correctly describe the dynamics
of the system under study? To answer this question, it is
necessary to find a solution to the original equations.
Such a solution can only be obtained by numerical
methods. This section presents the results of a numerical
analysis of the original equations. Immediately note that
the results obtained by numerical methods are in good
agreement with the analytical results obtained above.
For comparison the numerical solutions of the origi-
nal system of equations with the solutions of the short-
ened system of equations, we will set the initial values
of the interacting fields based on the equations of the
linear approximation of the original system.
To carry out a numerical analysis of the decay proc-
ess, it is convenient to introduce dimensionless variables
2
3
1 1 0
1
1
, , , ,
, ; ;
1,2,3 1,2 for waves, 3 for wave.
j p j
j z j
eE v n
i n n
mc c c n
t k kz
c
j j HF j LF
a a e
For numerical study of the decay dynamics of the
linearly polarized wave (Section 1.2), we rewrite the
system of equations (14) in the form:
* 31 2
1 2 3 2 1 3 3 1 2, ,V V V
aa a
a a aa aa . (23)
Here matrix elements 1 1 22pV c ,
2
2 12pV c , 3 1 2 22V k k c .
Note that by renormalizing the amplitudes in system
(23), the matrix elements 1 2 3, ,V V V can always be
transformed to the form when they are equal:
1 2 3V V V V (see [3]). For the numerical analysis of
the decay process, the following parameters of the sys-
tem were selected:
9 1
1 2.77 10f s is frequency of the
HF pump wave,
9 3
0 16 10n cm is plasma density,
ISSN 1562-6016. ВАНТ. 2021. № 4(134) 147
2 1 p is frequency of the excited HF-wave,
3 p is frequency of the excited LF-wave.
The graphs of the amplitudes dynamics 2 2 2
1 2 3, ,a a a
versus time are shown in Fig. 3 for stable and unstable
(for the case of decay of a linearly polarized wave) for
the set values of the wave amplitudes ( 0)j j a0 =a
a b
c d
e f
Fig. 3. Dependences of amplitudes 2 2
1 2
,a a , 2
3
a of waves
with linear polarization on time : a, b, e, f short-
ened; c, d the original system of equations.
Initial values: 1 0.01a0 , 2 0.001a0 (a-d);
3 0.03a0 (a, c); 3 0.0001a0 (b, d).
For V1=V2=V3=1: 1 0.001a0 , 2 0.0025a0 ;
3 0.01a0 (e); 1 0.01a0 , 2 0.001a0 , 3 0.0001a0 (f)
As can be seen from the graphs in Fig. 3, the magni-
tudes of the wave amplitudes are practically the same
both in the case of the shortened and the original system
of equations. In this case, the small difference in the
oscillation period of the amplitudes in the description of
the decay by the original and the shortened system of
equations is due to the inclusion of cubic and higher
order terms in nonlinearity in the original system of
equations. At equal values of the matrix elements, the
dynamics of the amplitudes of excited waves ( 2 2
2 3,a a )
practically coincides (see [3]).
The integrals of system (23) (known as the Manley-
Rowe relations) remain constant (with machine preci-
sion) over the entire computation time interval. It fol-
lows from these integrals that at the initial amplitudes
2 2
2 1 1 2(0) (0)V Va a and
2 2
3 1 1 3(0) (0)V Va a the
maximum values of the amplitudes of the decaying
waves, depending on the plasma density, are in the rela-
tion
2
3max 1 21
2
2max p
k k
a
a
. This dependence is con-
firmed by the results of numerical analysis.
The obtained results in their physical meaning fully
correspond to the results given in [3].
For a numerical analysis of wave decay with circular
polarization (Section 1.3), the system of equations (15)
is also convenient to rewrite in dimensionless variables
1,2
1,2
1
eA
mc
a 3
3,
a
c
a with the same matrix elements
1 2 3, ,V V V .
Graphs of amplitude dynamics versus time are
shown in Fig. 4 for decay of waves with circular polari-
zation when describing this decay by the shortened (26)
and the original initial system of equations.
a
b
Fig. 4. Dependences of amplitudes
2 2
2
1 2 3, ,
a a a
of waves with circular polarization on time : Initial
values of amplitudes 1 1 0.01 a0 a0 ,
2 2 0.001 a0 a0 , 3 0.0001a0 ;
shortened (a); the original system of equations (b)
As can be seen from the graphs in Fig. 4, with circu-
lar polarization of waves, the dynamics of the ampli-
tudes of high-frequency waves practically did not
change in comparison with the case of waves with linear
polarization, but the maximum amplitude of the excited
low-frequency wave the longitudinal velocity 3z a
significantly decreased.
If only waves of one circular polarization participate
in the decay of the type t t l , then such three-wave
interactions of the waves are suppressed.
The results of a numerical study confirm that in the
presence of waves of the one circular polarization:
1,2 1,2
(0) 0 and (0) 0 a a or
1,2 1,2
(0) 0 and (0) 0 a a the
amplitude of the LF wave remains constant, frequency
HF waves is 3 1 2HF a VV (Fig. 5).
Fig. 5. Dependence of the field amplitude 2
3a .
On time to time at: 1 0.01 a0 , 2 0.001 a0 ,
1 0.0 a0 , 2 0.0 a0 , 3 0.005a0
The same result takes place in the presence of waves
2
1 2 3, ,
a a a and in the absence of waves 1 2,
a a .
In the presence of an external magnetic field (Sec-
tion 1.4), the dynamics of the LF wave amplitude versus
time in the absence of one of the circularly polarized
waves completely coincides with the dynamics of the
LF wave amplitude in a system without a magnetic field
this amplitude remains constant regardless of the
magnitude of the external magnetic field.
ISSN 1562-6016. ВАНТ. 2021. № 4(134) 148
The influence of the detuning caused by the Faraday
effect (Section 1.5) on the decay dynamics will be ana-
lyzed by numerically solving the original system of
equations. The initial values for the fields were chosen
to satisfy the linear equations of this system of equa-
tions. From the condition for the existence of decay
(22), we introduce the threshold value of the pump wave
amplitude
3/2
0 2( ) / /H pthres H c , at which
the detuning value due to the external magnetic field
becomes equal to the increment of the decay process. So
with values 0 40H G (40) 0.02th .
a b
c d
Fig. 6. Dependences of amplitudes 2 2
1 2,x xa a , 2
3a on time
for various values of the magnetic field:
0 0H (a); 0 10H G (b); 0 25H G (c);
0 60H G (d). Initial field amplitudes:
1 0.02x a0 , 2 0.001x a0 ; 3 0.001a0
As can be seen from Fig. 6 with an increase in the
detuning parameter at 0 10H G (10) 0.005thres , the
strict periodicity of the dynamics amplitudes of high-
frequency waves was violated, the dynamics of the am-
plitudes of low-frequency waves remained practically
the same as at 0 0H with slightly lower maximum
values. With an increase in the detuning parameter at
0 25H G (25) 0.01thres , the dynamics of the LF
wave amplitude also changes qualitatively, and at
0 60H G (60) 0.03thres exceeds the initial pump
wave amplitude, which leads to the breakdown of the
wave decay process.
ACKNOWLEDGEMENTS
This work was partially supported by the Target
Program “Physics of Plasmas and Plasma Electronics:
fundamentals and applications” of the National Acade-
my of Sciences of Ukraine (Grant No. 0117U006867).
CONCLUSIONS
The examples considered above show that the whirl-
igig principle can be used not only to stabilize various
instabilities, but also as a tool to predict both the condi-
tions for stable states and the conditions for the devel-
opment of instabilities. In this work, with his help, it
was possible to determine the conditions under which
the interactions of waves in a magnetoactive plasma will
be unstable, as well as the conditions for the suppression
of these instabilities. These results allow us to point out
the range of parameters that must be selected to imple-
ment the required modes of wave interaction. In particu-
lar, it is shown that circularly polarized waves will be
stable with respect to decays.
REFERENCES
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3. B.B. Kadomtsev. Collective phenomena in plasma.
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Article received 16.06.2021
УПРАВЛЕНИЕ ПРОЦЕССАМИ ВЗАИМОДЕЙСТВИЯ ВОЛН В ПЛАЗМЕ
В.А. Буц, И.К. Ковальчук, А.П. Толстолужский, А.Г. Загородний
Изложены результаты исследования процессов нелинейного взаимодействия волн в плазме. Прежде все-
го рассмотрены механизмы управления процессами трехчастотного взаимодействия. Показано, что исполь-
зование принципa юлы позволяет указать на условия существования распадных процессов и на условия по-
давления процессов распада. Обнаружено, что отдельные волны с круговой поляризацией не распадаются в
плазме.
КЕРУВАННЯ ПРОЦЕСАМИ ВЗАЄМОДІЇ ХВИЛЬ У ПЛАЗМІ
В.О. Буц, І.К. Ковальчук, О.П. Толстолужський, А.Г. Загородній
Викладені результати дослідження процесів нелінійної взаємодії хвиль у плазмі. Насамперед розглянуті
механізми керування процесами тричастотної взаємодії. Показано, що використання принципу дзиґи
дозволяє вказати на умови існування розпадних процесів і на умови придушення процесів розпаду.
Виявлено, що окремі хвилі із круговою поляризацією не розпадаються в плазмі.
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