On the effective interaction of waves in inhomogeneous, nonstationary media

The description of new conditions of effective interaction of waves in periodically inhomogeneous and periodically nonstationary media is given. New conditions, as a special case, contain the known conditions of interaction of waves (synchronism conditions). Examples of the interaction of waves whic...

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Опубліковано в: :Вопросы атомной науки и техники
Дата:2017
Автори: Buts, V.A., Tolstoluzhsky, A.P.
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Опубліковано: Національний науковий центр «Харківський фізико-технічний інститут» НАН України 2017
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Цитувати:On the effective interaction of waves in inhomogeneous, nonstationary media / V.A. Buts, A.P. Tolstoluzhsky // Вопросы атомной науки и техники. — 2017. — № 6. — С. 71-75. — Бібліогр.: 6 назв. — англ.

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Digital Library of Periodicals of National Academy of Sciences of Ukraine
id nasplib_isofts_kiev_ua-123456789-136193
record_format dspace
spelling Buts, V.A.
Tolstoluzhsky, A.P.
2018-06-16T06:58:12Z
2018-06-16T06:58:12Z
2017
On the effective interaction of waves in inhomogeneous, nonstationary media / V.A. Buts, A.P. Tolstoluzhsky // Вопросы атомной науки и техники. — 2017. — № 6. — С. 71-75. — Бібліогр.: 6 назв. — англ.
1562-6016
PACS: 41.20.Jb; 02.30.Jr; 02.60.Cl
https://nasplib.isofts.kiev.ua/handle/123456789/136193
The description of new conditions of effective interaction of waves in periodically inhomogeneous and periodically nonstationary media is given. New conditions, as a special case, contain the known conditions of interaction of waves (synchronism conditions). Examples of the interaction of waves which characteristics satisfy the new interaction conditions are considered. These examples allow to detect new conditions in an experiment.
Даний опис нових умов ефективної взаємодії хвиль у періодично неоднорідних та нестаціонарних середовищах. Нові умови як окремий випадок містять відомі умови взаємодії хвиль (умови синхронізму). Розглянуто приклади взаємодії хвиль, характеристики яких задовольняють новим умовам взаємодії. Розглянуті приклади дозволяють виявити нові умови в експерименті.
Дано описание новых условий эффективного взаимодействия волн в периодически неоднородных и нестационарных средах. Новые условия, как частный случай, содержат известные условия взаимодействия волн (условия синхронизма). Рассмотрены примеры взаимодействия волн, характеристики которых удовлетворяют новым условиям взаимодействия. Рассмотренные примеры позволяют обнаружить новые условия в эксперименте.
en
Національний науковий центр «Харківський фізико-технічний інститут» НАН України
Вопросы атомной науки и техники
Динамика пучков
On the effective interaction of waves in inhomogeneous, nonstationary media
Про ефективну взаємодію хвиль у неоднорідних, нестаціонарних середовищах
Об эффективном взаимодействии волн в неоднородных, нестационарных средах
Article
published earlier
institution Digital Library of Periodicals of National Academy of Sciences of Ukraine
collection DSpace DC
title On the effective interaction of waves in inhomogeneous, nonstationary media
spellingShingle On the effective interaction of waves in inhomogeneous, nonstationary media
Buts, V.A.
Tolstoluzhsky, A.P.
Динамика пучков
title_short On the effective interaction of waves in inhomogeneous, nonstationary media
title_full On the effective interaction of waves in inhomogeneous, nonstationary media
title_fullStr On the effective interaction of waves in inhomogeneous, nonstationary media
title_full_unstemmed On the effective interaction of waves in inhomogeneous, nonstationary media
title_sort on the effective interaction of waves in inhomogeneous, nonstationary media
author Buts, V.A.
Tolstoluzhsky, A.P.
author_facet Buts, V.A.
Tolstoluzhsky, A.P.
topic Динамика пучков
topic_facet Динамика пучков
publishDate 2017
language English
container_title Вопросы атомной науки и техники
publisher Національний науковий центр «Харківський фізико-технічний інститут» НАН України
format Article
title_alt Про ефективну взаємодію хвиль у неоднорідних, нестаціонарних середовищах
Об эффективном взаимодействии волн в неоднородных, нестационарных средах
description The description of new conditions of effective interaction of waves in periodically inhomogeneous and periodically nonstationary media is given. New conditions, as a special case, contain the known conditions of interaction of waves (synchronism conditions). Examples of the interaction of waves which characteristics satisfy the new interaction conditions are considered. These examples allow to detect new conditions in an experiment. Даний опис нових умов ефективної взаємодії хвиль у періодично неоднорідних та нестаціонарних середовищах. Нові умови як окремий випадок містять відомі умови взаємодії хвиль (умови синхронізму). Розглянуто приклади взаємодії хвиль, характеристики яких задовольняють новим умовам взаємодії. Розглянуті приклади дозволяють виявити нові умови в експерименті. Дано описание новых условий эффективного взаимодействия волн в периодически неоднородных и нестационарных средах. Новые условия, как частный случай, содержат известные условия взаимодействия волн (условия синхронизма). Рассмотрены примеры взаимодействия волн, характеристики которых удовлетворяют новым условиям взаимодействия. Рассмотренные примеры позволяют обнаружить новые условия в эксперименте.
issn 1562-6016
url https://nasplib.isofts.kiev.ua/handle/123456789/136193
citation_txt On the effective interaction of waves in inhomogeneous, nonstationary media / V.A. Buts, A.P. Tolstoluzhsky // Вопросы атомной науки и техники. — 2017. — № 6. — С. 71-75. — Бібліогр.: 6 назв. — англ.
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fulltext ISSN 1562-6016. ВАНТ. 2017. №6(112) 71 ON THE EFFECTIVE INTERACTION OF WAVES IN INHOMOGENEOUS, NONSTATIONARY MEDIA V.A. Buts 1,2,3 , A.P. Tolstoluzhsky 1 1 National Science Center “Kharkov Institute of Physics and Technology”, Kharkov, Ukraine; 2 V.N. Karazin Kharkiv National University, Kharkov, Ukraine; 3 Institute of Radio Astronomy of the National Academy of Sciences of Ukraine (IRA NASU), Kharkov, Ukraine The description of new conditions of effective interaction of waves in periodically inhomogeneous and periodi- cally nonstationary media is given. New conditions, as a special case, contain the known conditions of interaction of waves (synchronism conditions). Examples of the interaction of waves which characteristics satisfy the new interac- tion conditions are considered. These examples allow to detect new conditions in an experiment. PACS: 41.20.Jb; 02.30.Jr; 02.60.Cl INTRODUCTION It is known that the effective interaction of waves in weakly inhomogeneous, nonstationary and nonlinear media occurs when the following conditions are ful- filled: k 0i i k   , 0i i     . These condi- tions mean that the detuning of the frequencies and wave vectors of the interacting waves should be mini- mal (see, for example, [1 - 3]). This also means that the synchronism conditions between the interacting waves must be satisfied along each of the four axes of the four- dimensional space-time space. We note that often these four conditions are called the laws of conservation of energy and momentum in the interaction of waves. In- deed, if each of these conditions is multiplied by the Planck constant, then these are the laws of conservation of energy and momenta in the interaction of individual photons with each other. In our previous works [4, 5] it was shown that in the general case, in some distributed systems, some other relationships for the frequencies and wave vectors of the interacting waves can be per- formed for effective wave interaction. This possibility is due to the fact that detuning along one of the directions of the four-dimensional space can be compensated by detunings along other directions. As a result, certain lines (characteristic lines) can be identified in space along which an effective exchange of energy is possible. Effective exchange occurs, in spite of the fact that the known conditions of interaction between waves (see above) are not fulfilled. In this paper we consider the simplest examples of the realization of such a wave in- teraction. It is shown that in the interaction of two waves in an inhomogeneous nonstationary medium, can arise the waves, whose frequencies do not satisfy the known conditions given above. 1. PROBLEM STATEMENT. BASIC EQUATIONS Let's consider a medium whose permittivity can be represented as two terms. The first term is a constant. The second term is assumed small, but is a periodic function of space and time. As an example, we can con- sider the following expression for such a permittivity: 0 , cos( ), 1.q r t q         (1) Let two electromagnetic waves propagate in such a medium, the wave frequencies of which are different. We will be interested in the conditions for the effective interaction of these waves in such a medium. The equa- tions for each of these waves are the Maxwell equation. From the Maxwell equations it is easy to find the equa- tions for the electric field vectors of each of these elec- tromagnetic waves: 2 2 2 1 ( ) 1 . E E E c t                (2) By assumption, we have two waves, so we will seek the solution of (2) as the sum of two terms: 0 0 0 1 1 1( , )exp( ) ( , )exp( ),E A r t i t ik r A r t i t ik r       (3) here 2 2 2 2 2 2 0 0 0 1 1 0/ , /k c k c     . Let us consider the simplest case, which shows the most important characteristics of the new interaction conditions and which, apparently, is most easily realized in the experiment. We will assume that the interaction occurs between transverse waves, that the medium is periodically non-uniform in only one direction (in the z direction). In this case, the time detuning can be com- pensated only by a detuning along the z axis. Moreover, we will assume that the waves are located on one dis- persion linear branch. In this case, the phase velocities of the waves and their group velocities coincide. As will be seen below, all of these restrictions are non-essential (they are imposed only to simplify the formulas) and, if necessary, can be easily removed. We will also assume that the waves propagate only in one direction  in the direction of the axis. In this case, substituting (3) in (2), we can obtain the following equations for finding the amplitudes iA :     2 2 0 0 0 0 0 0 0 02 2 2 2 2 1 12 2 2 0 0 11 1 1 1 12 2 2 2 2 0 02 2 exp ( , ) , 2 2 exp ( , ) , 2 A A A A i k z tz c t c q A i z t c A A A A i k z tz c t c q A i z t c                                                                  (4) where ( , )r t k r t      ,  1 0k k k     , 1 0 .      ISSN 1562-6016. ВАНТ. 2017. №6(112) 72 This system is regorous. It is supposed that the de- tuning  though is arbitrary however it is chosen in such a way that only these two waves can interact. Characteristics of the equations (4) without the second derivatives (i.e. subcharacteristics) are parallel to straight lines: ( , )r t k z t const       . It means that derivatives along these subcharacteris- tics are equal to zero: 0      , here z   , 0/t c   . The interaction of waves is due to the small inhomo- geneity ( 1q  ) of the dielectric constant. It is natural to expect that the wave amplitudes will change slowly. Therefore, in the system of equations (4), we can omit the second derivatives. It should be noted that this assumption always re- quires additional analysis. In particular, as a minimum, the obtaining solutions should be tested to satisfy this assumption. We note that taking into account the second derivatives in the system of equations (4), of course, opens the possibility of the appearance of new solutions, which may be interesting in their own way. However, the questions arises: "How the presence of second derivatives can change solutions that are ob- tained without taking into account these derivatives." Will the solutions obtained (within the framework of accounting only the first derivatives) be stable with re- spect to accounting for second derivatives? "This ques- tion can be quite easily studied. Indeed, following [6], we consider one equation from system (4), in which we omit the right-hand side: 2 2 2 2 0 A A A A z z                    . (5) In equation (5)  and   are arbitrary constants. Add the following new variable: z   . Equation (5) in the new variables has the form:     2 4 A A A                     . (6) We will consider the dynamics of the jumps along the sub-characteristics: 0z const      and 0z const      . For example, the amplitude jump at propagation along the subcharacteristic 0 const   has form: 0 0( , ) ( , ) A A s              . (7) Substituting into Eq. (6) one by one 0   and 0   , also combining obtained the equations, we find the following equation, which describes the dynamics of jump:  4 s s       . (8) From this equation it follows that the dynamics will be stable if the following conditions are fullfield: Re( ) 0   . Similarly, we can find the stability con- dition for the solution as the jump propagates along the second subcharacteristic. Finally, the stability condi- tions for the solutions obtained by neglecting the second derivatives will look: Re( ) 0   , Re( ) 0   . (9) These conditions are quite general. They are suitable for the stability analysis in many applied problems. For example, in the case of the propagation of wave beams in inhomogeneous, nonstationary and nonlinear media. In our case, it is easy to see that the coefficients  and  purely imaginary. This means that in our case the second derivatives are unable to radically change the dynamics of the solutions obtained considering only the first derivatives. We drop the second derivatives on the left-hand side of system (4). Then the left-hand side of these equations can be regarded as a derivative along the characteristic lines: z C const     . Moreover, these directions for interacting waves coincide. We also pay attention to the fact that the right-hand sides of the system of equa- tions (4) contain complex conjugate factors  exp ( , )i z t . In this case, taking into account that 0      or 0/k c     (10) in the system of equations (4) differentiating the left and right sides of the equations with respect to the new vari- able, we obtain the following equations for determining the amplitudes 0A and 1A :   2 2 2 0 0,1i i A K A i        , (11) where  2 2 0 1 / 64K q k k  . Solutions of equations (11) can be, for example, functions: 0 cos( )A a   , 1 sin( )A b   . This choice of solutions, in particular, can mean that there is a periodic transfer of energy from one wave to the second wave in the process of their interaction. The interaction of waves considered above occurs when they propagate in the same direction, in the direc- tion of the positive z axis ( 0 10, 0k k  ). It is easy to show that if they propagate in the opposite direction ( 0 10, 0k k  ), then the interaction will occur under the same laws of interaction. However, this interaction will occur along another subcharacteristic. Namely, along z   . In this case, the system of equations (11) will be transformed into a system of equations: 2 2 2 0,i i A K A       (12) where z   ,  0,1i  . 2. INTERACTION IN THE LAYER In this paper we study new conditions for the effec- tive interaction of waves in inhomogeneous media. In addition to general theoretical considerations, it is of interest to consider some simple case in which the basic elements of the new interaction conditions under con- sideration were contained and that would be as simple as possible so that they could be realized in the experi- ISSN 1562-6016. ВАНТ. 2017. №6(112) 73 ment. In this section such case will be considered. It is a layer of thickness L of an inhomogeneous medium. The boundaries of the layer are ideally reflective. Inside the layer, two waves propagate perpendicular to its boundaries. Each of these waves represents the sum of two waves, one of which propagates along the z axis, and the other is a wave reflected from the boundary (Fig. 1). Fig. 1. Interacting waves in layer Dynamics of interaction of each of these waves has been described above. Expression for the field compo- nents in such a system can be represented in such form:         0 0 0 1 1 1 0 0 0 1 1 1 A exp( ) exp( ) exp( ) Cexp( ) exp( ) exp( ), A exp( ) exp( ) exp( ) Cexp( ) exp( ) exp( ). x y E ik z B ik z i t ik z D ik z i t H ik z B ik z i t ik z D ik z i t                             (13) In formula (13)  is homogeneous part (constant) dielectric permeability of the layer 0 , 1z L    , but , , ,A B C D are slow functions of time and coordinate. The analytical type of these functions is determined by the solutions of equations (11) and (12). To determine the constants of these functions, it is necessary to use the boundary conditions. In this case, they are simple: 0 :z  0; 0A B C D    . :z L 0 0 1 1 ( ) exp( ) ( )exp( ) 0; exp( ) exp( ) 0. A L ik L B L ik L C ik L D ik L        (14) In the system equations (14) functions , , ,A B C D can be presented in the form: exp(i )A a    ; exp( i )B b     ; exp(i )C c    ; exp( i )D d     . (15) In the expressions (15) a,b, ,dc constants. Taking these expressions into account, the algebraic system of equations (14) can be rewritten as follows: 0 :z  a b  ; c d  . :z L    0 0exp ( ) exp ( )a i k L i b i k L i            . (16) We note that for the effective interaction of waves in the considered dielectric layer, it is necessary that the wave numbers satisfy the following relation:  0k L n  . (17) Taking into account the relations (16), the expres- sion for the electric component of the total field in the layer can be expressed by the following formula:         0 0 0 0 1 1 12 1 sin exp 2 e sin exp 4 i k z i E ia k k k k z i k                           (18) or         0 0 0 0 1 1 12 1 Re sin sin sin sin . 4 E a k z k k k a k z k                           . (19) 3. INVESTIGATION OF THE DYNAMICS OF INTERACTION OF WAVES BY NUMERICAL METHODS Conditions of the effective interaction of waves in inhomogeneous media have been verified by numerical methods. For this purpose introducing new dimension- less variables 0 1 0 0 1/ ;k k t c k k z       , and also introducing new dimensionless amplitudes 0 0 3 34 0 1 1 ( , ) ( , )a A k k       , 1 1 3 34 0 1 1 ( , ) ( , )a A k k       from (4) (without taking into account the second deriva- tives) we will obtain the system of equations for the first derivatives in the form:     0 0 1 1 1 0 exp ( , ) , 4 exp ( , ) . 4 a a q a i i a a q a i i                               (20) Here ( , ) k          and introduce dimen- sionless detunes 01 0 1 0 1 kk k k k k k            , 001 0 1 0 1 kk k k c k k               . The initial and boundary conditions are chosen in accordance with the analytical solutions. Amplitude value of the field 0 1a  . The parameter 0.8, 0.1q  . The results of the analytical and numerical analysis of the system of first-order equations obtained from (4) are presented in Figs. 2-4. In Fig. 2 at 0.8q  presented dynamics of the interaction of waves for the case of ful- fillment of known synchronism conditions ( 0k     ), also for the case of identical detunings ( 0k     ). As can be seen from this plot, the dy- namics of the interaction of waves is practically the same. If there is a detuning along one of the directions (for ex- ample 1.095k  ), there is no effective interaction be- tween the waves (Fig. 3). Analytic and numerical solu- tions coincide with a good degree of accuracy. Fig. 2. Analytic and numerical values of the field ampli- tudes along the line   for detuning 0k     , 1.095k     , 0.707k     , 0.8q  , 0Re( )a  red line, 1Im( )a  blue line (dotted line) Fig. 3 shows that the interaction of waves is practi- cally absent. Indeed, the amplitude of the wave oscilla- tions, which is caused by interaction with other waves in 1 0 0 L z ISSN 1562-6016. ВАНТ. 2017. №6(112) 74 absolute magnitude, is negligible. Besides, it is seen that the frequency of these oscillations of the amplitude cor- responds to the value of detuning. Fig. 3. Value of amplitude 0Re( )a along the line   for detuning 1.095k  , 0  ; 0.1q  Fig. 4. Plots of amplitude 0Re( )a a – 0k     , b – 0.707k     ; 0.8q  Fig. 4 shows that both in the case of the known syn- chronism conditions and in the case of equal detunings, the amplitude of the initial wave varies periodically along the characteristic line   . Notice that under the known conditions of synchronism the real part of the amplitude of the initial wave is strictly transferred into the imaginary part of the second wave and back. When the new conditions are fulfilled, the energy exchange process is more complicated, which is represent in Fig. 4,b. It should also be noted that, unlike the known synchronism conditions, in which the energy exchange between waves can be observed in the ordinary space, the energy exchange between the waves in the presence of detunings in the general case is effectively observed along the selected subcharacteristic. This feature of the interaction of waves in the presence of detuning is clear- ly visible from Fig. 2 at 1.095k     . CONCLUSIONS Thus, the results obtained above show that, in addi- tion to the known conditions for the effective interaction of waves ( 0k     ), there are more general condi- tions for energy exchange between the waves. In the case considered above, these conditions have a simple form k c     . Under these conditions, detunings k and   are almost arbitrary values. As can be seen, these new conditions contain, as a particu- lar case, known synchronism conditions 0k     . To visually see the difference in old and new condi- tions, in the Fig. 5 shows an example of waves which can effectively interact is presented. If to use the known conditions of interaction, then for most of these waves they can't be fulfilled. We use the new conditions of synchronicity. It is easy to see that any triplets of waves that are represented in the figure satisfy the new syn- chronism conditions /k c    . They can effi- ciently exchange energy. There are infinitely many such triples. An important example of the conditions under con- sideration is an example of the interaction of waves in a plane layer, which was considered above. Indeed, as can be seen from the formula (19), the expression for the real component of the electric field can be easily meas- ured in real experiments. It can be seen that the appear- ance of waves with new frequencies ( 1 ) can easily be observed if at the initial point of time only one wave with a frequency ( 1 ), in a layer there was only one wave with a frequency ( 0 ). Fig. 5. Dispersion effectively interaction of waves at 0k     If we consider an unbounded region of interaction, then the new synchronism conditions are not very con- venient to observe. They can effectively manifest them- selves, for example, in systems with electron beams. In other cases, it is rather difficult to observe these condi- tions. However, if the wave interaction region is bound- ed, for example, as was done in Section 3 above, then it follows from formulas (18), (19) that it is easy to observe these conditions. Indeed, it is enough to fix the probe at an arbitrary point in the layer. And in time, the probe will appear oscillations both at the frequency of the original wave and at frequencies that might not appear when the known synchronism conditions are fulfilled. REFERENCES 1. G.M. Zaslavsky, R.Z. Sagdeev. Introduction to Non- linear Physics: From the Pendulum to Turbulence and Chaos. M.: “Nauka”, 1988, 368 p. (in Russian). 2. B.B. Kadomtsev. Collective Phenomena in Plasmas. M.: “Nauka”, 1976, 238 p. (in Russian). 3. J. Weiland, H. Wilhelmsson. Coherent Nonlinear Interaction of Waves in Plasmas. М.: “Energoizdat”, 1981, 224 p. (in Russian). 4. V.A. Buts. On Conditions of Synchronism at Waves Interaction in Inhomogeneous, Nonstationary and Nonlinear Media // Achievments of Modern Radioe- lectronic. 2009, № 5, p. 13-22. 5. V.A. Buts. About conditions of effective interaction of waves in non-uniform, non-stationary and nonlin- ear medium // Problems of Atomic Science and Technology. Series “Plasma Physics”. 2010, № 6, p. 117-119. 6. Julian D. Cole. Perturbation Methods In Applied Mathematics. London: Blaisdell Publishing Compa- ny, Toronto, 1968. Article received 11.10.2017 ISSN 1562-6016. ВАНТ. 2017. №6(112) 75 ОБ ЭФФЕКТИВНОМ ВЗАИМОДЕЙСТВИИ ВОЛН В НЕОДНОРОДНЫХ, НЕСТАЦИОНАРНЫХ СРЕДАХ В.А. Буц, А.П. Толстолужский Дано описание новых условий эффективного взаимодействия волн в периодически неоднородных и не- стационарных средах. Новые условия, как частный случай, содержат известные условия взаимодействия волн (условия синхронизма). Рассмотрены примеры взаимодействия волн, характеристики которых удовле- творяют новым условиям взаимодействия. Рассмотренные примеры позволяют обнаружить новые условия в эксперименте. ПРО ЕФЕКТИВНУ ВЗАЄМОДІЮ ХВИЛЬ У НЕОДНОРІДНИХ, НЕСТАЦІОНАРНИХ СЕРЕДОВИЩАХ В.О. Буц, О.П. Толстолужський Даний опис нових умов ефективної взаємодії хвиль у періодично неоднорідних та нестаціонарних сере- довищах. Нові умови як окремий випадок містять відомі умови взаємодії хвиль (умови синхронізму). Розг- лянуто приклади взаємодії хвиль, характеристики яких задовольняють новим умовам взаємодії. Розглянуті приклади дозволяють виявити нові умови в експерименті.