Effect of dust particles on electron energydistribution in glow and afterglow plasmas

Analytical expressions describing electron energy probability functions (EEPFs) in glow and afterglow dusty plasmas are obtained from the homogeneous Boltzmann equation for electrons. At large energies in a glow dusty plasma, the quasiclassical approach for calculation of the EEPF is applied. Cons...

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Дата:2016
Автори: Denysenko, I.B., Azarenkov, N.A., Ivko, S., Burmaka, G., Glazkov, A.
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Опубліковано: Національний науковий центр «Харківський фізико-технічний інститут» НАН України 2016
Назва видання:Вопросы атомной науки и техники
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Цитувати:Effect of dust particles on electron energydistribution in glow and afterglow plasmas / I.B. Denysenko, N.A. Azarenkov, S. Ivko, G. Burmaka, A. Glazkov // Вопросы атомной науки и техники. — 2016. — № 6. — С. 179-182. — Бібліогр.: 9 назв. — англ.

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spelling nasplib_isofts_kiev_ua-123456789-1154452025-02-09T17:01:25Z Effect of dust particles on electron energydistribution in glow and afterglow plasmas Влияние пылевых частиц на распределение электронов по энергии в плазме в режимах свечения и послесвечения Вплив пилових частинок на розподіл електронів за енергією в плазмі в режимах світіння та післясвітіння Denysenko, I.B. Azarenkov, N.A. Ivko, S. Burmaka, G. Glazkov, A. Iter and fusion reactor aspects Analytical expressions describing electron energy probability functions (EEPFs) in glow and afterglow dusty plasmas are obtained from the homogeneous Boltzmann equation for electrons. At large energies in a glow dusty plasma, the quasiclassical approach for calculation of the EEPF is applied. Considering the afterglow case, the analytical expressions are obtained assuming that the electron energy loss is mainly due to momentum-transfer electronneutral collisions and due to deposition of electrons on dust particles. Effect of dust particles on the EEPF is analyzed. Из однородного уравнения Больцмана получены аналитические выражения для функции распределения электронов по энергии (ФРЭЭ) в пылевой плазме в режимах свечения и послесвечения. Для расчёта ФРЭЭ в режиме свечения при больших электронных энергиях применён квазиклассический подход. Для плазмы в режиме послесвечения аналитические выражения получены в предположении, что потери энергии электронов происходят в основном за счёт упругих электрон-нейтральных столкновений и благодаря осаждению электронов на пылевые частицы. Проанализировано влияние пылевых частиц на ФРЭЭ. З однорідного рівняння Больцмана отримано аналітичні вирази для функції розподілу електронів за енергією (ФРЕЕ) в запорошеної плазмi в режимах світіння та післясвітіння. Для розрахунку ФРЕЕ в режимі світіння при великих електронних енергіях застосовано квазікласичний підхід. Для плазми в режимі післясвітіння аналітичні вирази отримані в припущенні, що втрати енергії електронів відбуваються в основному за рахунок пружних електрон-нейтральних зіткнень та завдяки осадженню електронів на пилові частинки. Проаналізовано вплив пилових частинок на ФРЕЕ. This work was supported by the State Fund for Fundamental Research of Ukraine. 2016 Article Effect of dust particles on electron energydistribution in glow and afterglow plasmas / I.B. Denysenko, N.A. Azarenkov, S. Ivko, G. Burmaka, A. Glazkov // Вопросы атомной науки и техники. — 2016. — № 6. — С. 179-182. — Бібліогр.: 9 назв. — англ. 1562-6016 PACS: 52.25.Vy, 52.27.Lw, 51.50.+v, 52.80.Pi https://nasplib.isofts.kiev.ua/handle/123456789/115445 en Вопросы атомной науки и техники application/pdf Національний науковий центр «Харківський фізико-технічний інститут» НАН України
institution Digital Library of Periodicals of National Academy of Sciences of Ukraine
collection DSpace DC
language English
topic Iter and fusion reactor aspects
Iter and fusion reactor aspects
spellingShingle Iter and fusion reactor aspects
Iter and fusion reactor aspects
Denysenko, I.B.
Azarenkov, N.A.
Ivko, S.
Burmaka, G.
Glazkov, A.
Effect of dust particles on electron energydistribution in glow and afterglow plasmas
Вопросы атомной науки и техники
description Analytical expressions describing electron energy probability functions (EEPFs) in glow and afterglow dusty plasmas are obtained from the homogeneous Boltzmann equation for electrons. At large energies in a glow dusty plasma, the quasiclassical approach for calculation of the EEPF is applied. Considering the afterglow case, the analytical expressions are obtained assuming that the electron energy loss is mainly due to momentum-transfer electronneutral collisions and due to deposition of electrons on dust particles. Effect of dust particles on the EEPF is analyzed.
format Article
author Denysenko, I.B.
Azarenkov, N.A.
Ivko, S.
Burmaka, G.
Glazkov, A.
author_facet Denysenko, I.B.
Azarenkov, N.A.
Ivko, S.
Burmaka, G.
Glazkov, A.
author_sort Denysenko, I.B.
title Effect of dust particles on electron energydistribution in glow and afterglow plasmas
title_short Effect of dust particles on electron energydistribution in glow and afterglow plasmas
title_full Effect of dust particles on electron energydistribution in glow and afterglow plasmas
title_fullStr Effect of dust particles on electron energydistribution in glow and afterglow plasmas
title_full_unstemmed Effect of dust particles on electron energydistribution in glow and afterglow plasmas
title_sort effect of dust particles on electron energydistribution in glow and afterglow plasmas
publisher Національний науковий центр «Харківський фізико-технічний інститут» НАН України
publishDate 2016
topic_facet Iter and fusion reactor aspects
url https://nasplib.isofts.kiev.ua/handle/123456789/115445
citation_txt Effect of dust particles on electron energydistribution in glow and afterglow plasmas / I.B. Denysenko, N.A. Azarenkov, S. Ivko, G. Burmaka, A. Glazkov // Вопросы атомной науки и техники. — 2016. — № 6. — С. 179-182. — Бібліогр.: 9 назв. — англ.
series Вопросы атомной науки и техники
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fulltext ISSN 1562-6016. ВАНТ. 2016. №6(106) PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2016, № 6. Series: Plasma Physics (22), p. 179-182. 179 EFFECT OF DUST PARTICLES ON ELECTRON ENERGYDISTRIBUTION IN GLOW AND AFTERGLOW PLASMAS I.B. Denysenko, N.A. Azarenkov, S. Ivko, G. Burmaka, A. Glazkov School of Physics and Technology, V.N. Karazin Kharkiv National University, Kharkov, Ukraine E-mail: idenysenko@yahoo.com Analytical expressions describing electron energy probability functions (EEPFs) in glow and afterglow dusty plasmas are obtained from the homogeneous Boltzmann equation for electrons. At large energies in a glow dusty plasma, the quasiclassical approach for calculation of the EEPF is applied. Considering the afterglow case, the ana- lytical expressions are obtained assuming that the electron energy loss is mainly due to momentum-transfer electron- neutral collisions and due to deposition of electrons on dust particles. Effect of dust particles on the EEPF is ana- lyzed. PACS: 52.25.Vy, 52.27.Lw, 51.50.+v, 52.80.Pi INTRODUCTION Dusty plasmas have been extensively studied in the last three decades because these complex ionized gas systems are of great interest in different fields [1-5]. At theoretical description of dusty plasmas, one usually assumes that electrons are in Maxwellian equilibrium [1, 2]. However, for most of industrial and laboratory plasmas, the electron energy probability function (EEPF) often deviates from Maxwellian because of the many different electron collision processes [3]. The profile of electron energy probability function affects different plasma parameters. Therefore, determination of the EEPF profile is very important in studying of different plasmas. For calculation of the EEPF in dusty plasmas, usually different numerical approaches are used. Here, we present analytical expressions describing the EEPF in glow and afterglow dusty plasmas. 1. MAIN EQUATIONS AND ASSUMPTIONS We consider an argon dusty plasma maintained by an electric field )(tE . Plasma consists of electrons, ions with number densities ne and ni, respectively, and of dust particles of submicron size with density dn and radius da . The plasma is assumed to be quasineutral, i.e., idde nZnn  , where dZ is the dust charge (in units of electron charge e). It is also supposed that the ions have Maxwellian distribution with temperature iT (= 0.026eV), but the electron energy probability func- tion F in general is not Maxwellian and satisfies to the homogeneous Boltzmann equation [6]:  FS u tuF E v u uum e t tuF me              ),( 3 2),( 2 2/3 , (1) where u is the electron energy (in eV), t is the time, me is the electron mass, 22 22 p2 )( )( 2   uv uvE E m m for the RF case, and pEE  is the external electric field in the DC case. Here, pE is the RF field amplitude, Ef 2 , and Ef is the RF frequency. em e edm   , where e ed and em are the frequencies for momentum-transfer electron-dust and electron-atom collisions.  FS =Sea(F) +Sed(F), where Sea(F) and Sed(F) are the terms describ- ing electron-atom and electron-dust collisions, respec- tively [3, 4]. We consider low-ionized dusty plasma, therefore, electron-electron collisions are not accounted for in the model. The homogeneous Boltzmann equation (1) may be used if the energy relaxation length is small compared to the spatial inhomogeneity scale of the dis- charge. For the case of a glow dusty plasma and for the afterglow with low dust density, the EEPF can be pre- sented in the form F0 = nef0(u). The function f0 is nor- malized by 1)( 0 0   duuuf . It is assumed that the electron (Ie ) and ion ( Ii ) cur- rents to a floating dust particle are in balance, or Ie + Ii=0. The electron and ion currents to a dust particle are calculated using the orbit-motion-limited (OML) theory, taking into account the ion-neutral collisions in the sheath around a dust particle [1, 2, 4]. In general, the EEPF from Eq. (1) may be found only numerically. However, as it will be shown below, approximate ana- lytical solutions of Eq. (1) also exist. 2. THE APPROXIMATE ANALYTICAL SO- LUTIONS FOR THE EEPF IN GLOW DUSTY PLASMA Assuming that the number of electrons with energy larger than the first excitation energy threshold ( *u 5.11 eV for Ar) is small, one can neglect by trans- formation of electrons with large energy into low- energetic electrons, and the term describing inelastic electron-atom collisions can be presented in the follow- ing form [6]       k k ea exc ea uuFuvFS ,2/1 where v k ea is the collision frequency of the k-th inelastic process with a threshold energy Vk.. As a result, the homogeneous Boltzmann equation (1) can be written as 3/2 0 0 1 0 ( ) ( ( ( ) ( )) 1 ) ( )) ( ( ) ( ) , e D ed em c ed f u u f u u u f u u u u u u                          (2) 180 ISSN 1562-6016. ВАНТ. 2016. №6(106) where  =2me/ma, D =2me/md, am and dm are the masses of neutral gas atoms and dust particles, respec- tively )(3 2 2 1 em e edDme g E m e T     ,   k k ea uvu)(1 is the total frequency for inelastic electron-atom collisions including processes of excita- tion and ionization, c ed is the frequency describing dep- osition of electrons on dust particles [4]. At large electron energies ( 5.11** 1  uuu eV, and by taking * 1u = 20 eV), the electron energy probability function decreases rapidly with an increase of u. There- fore, the quasiclassical approach can be applied for cal- culation of the EEPF at large electron energies, and [6]: ))(exp()( 20 uSCuf  , (3) where 2C is a constant, and // 1 * 1 )()( duuuS u u   with )()( )]()([1 )( 1 1 uu uu u u em e edD c ed        . At large electron energies the EEPF in a dusty plasma decreases faster than in a dust-free plasma because the ratio of 1 in a dusty plasma to that in a dust-free plas- ma for the same electric field sustaining the plasmas is approximately )( )()( 1 1 u uuc ed     . The decrease increas- es with an increase of nd or ad. To calculate the EEPF at moderate and low energies )( * 1uu  , we move from u to the new variable uuy  * 1 . In this case, Eq. (3) can be presented in the following form )4()()]()([ )(1 )()( * 101 0 0 yuyfyy y yf yfy y c ed                       where ))()(()( 2/3 uuuy em e edD   with yuu  * 1 . It follows from Eq. (4) that )5(,)(exp )(exp)()()( 0 // / 0 0 ////// 20 /                               y y y dyy dydyyyyCyf   where )( )()]()([ )( / 0 /* 1 / 0 / 1 / y dyyuyfyyA y y c ed        . To obtain Eq. (5), we assumed that the EEPF and it’s derivative on energy are continious at * 1uu  . The constant C2 in Eqs. (3) and (5) can be found from the normalization condition           1)( 0 0 duuuf . Dusty plasma parameters (the EEPF, effective electron tem- perature and dust charge) obtained using Eqs. (3) and (5) were compared with those calculated numerically by a finite-difference method with accounting for electron- electron collisions and transformation of high-energy electrons into low-energetic electrons at inelastic elec- tron-neutral collisions. It was found that the analytical expressions (3) and (5) can be used for calculation of the EEPF and dusty plasma parameters at typical exper- imental conditions [7], in particular, in the positive col- umn of a direct-current glow discharge and in the case of an RF plasma maintained by an electric field with frequency f=13.56 MHz. Moreover, in a 13.56 MHz plasma, the EEPF may become close to the Maxwellian distribution at an increase of dust density. That is in a qualitative agreement with numerical and experimental results of previous authors [4, 7]. 3. THE APPROXIMATE ANALYTICAL SOLUTION FOR THE EEPF IN DUSTY PLASMA AFTERGLOW Now consider a dusty plasma afterglow. The after- glow has the two characteristic times [6]: 1 1 )(  um and 1 12 )()(    uu c ed , where  ... denotes the averaging on time. The time 2 de- termines the energy relaxation of electrons with large energy ( *uu  ). 1 is the time for energy relaxation of electrons in the EEPF core (with *uu  ). For *uu  , )()(1 uu m  , and, therefore, 12   [6]. In the afterglow, the number of electrons decreases first in the tail of the EEPF, and essential changes in the EEPF core take place at larger afterglow times ( 2t ). Here, we will consider the afterglow times larger than 2 . For these times, the effect of inelastic electron- atom collisions on the EEPF is small, and                       u F TFuvu m m uu FS gm a e ea 2/321 , (6) where Tg is the neutral gas temperature, which is as- sumed to be equal to 300 K (0.026 eV). It is supposed that the average electron energy is larger than the neutral gas temperature. We also assume that for the most of electron energies considered here the electron-atom elastic collisions dominate over the electron-dust momentum-transfer collisions. Therefore, the term in Eq. (1) describing electron-dust collisions simplifies to   FtuvFS c eded ),( , where e c edd c ed meutuntu /2),(),(   is the frequency describing collection of electrons by dust particles with the cross- section σ c ed( u ) = πa 2 d(1– φs(t) / u ) for u ≥ φs(t) and 0 for u < φs(t). Here, φs(t) is the absolute val- ue of dust surface potential. Taking into account these assumptions, Eq. (1) simplifies to the following equa- tion: ISSN 1562-6016. ВАНТ. 2016. №6(106) 181   .0),(),( ),()( 1),( 2/3        tutuF tuFuu uut tuF c ed m   (7) Here, we assume that the time-dependencies for dust charge  tZd and dust surface potential  ts are expo- nential:    /exp0 tZtZ dd  ,     /exp0 tt ss  , where  00  tss  ,  00  tZZ dd , and  is the time characterizing the dust charge decrease in after- glow. In this case,   uuttu s c ed )//exp1(),( 0   for  tu s , where edd man /22  . In this study, it is also assumed that the frequency for electron-atom collisions does not depend on electron energy ( constm  ) and the EEPF for t = 0 can be pre- sented in the following form [8] )exp()0,( 21 xuAAuF  , (8) where x is a number. For Maxwellian and Druyvesteyn EEPFs, x = 1 and x = 2, correspondingly. x xu A           )( )(1 1 2 2   , where )2/(31 x , )2/(52 x , dttt )exp()( 0 1     with  >0 is the gamma function, and  u is the mean energy of electrons, which is connected with the effec- tive electron temperature by expression effTu 2 3  . If  u << *u , then 2/5 1 2/3 2 2/31 )]([ )]([       u x A . Taking into account these assumptions and using the method of characteristics [9], one gets from Eq. (7) for  tu s the following expression for the EEPF: )2/3exp(),( 21 txxeuAtAtuF   . (9) If the initial EEPF is Maxwellian, the previous ex- pression coincides with that presented in [6]: )2/3exp()exp(exp),( tt T u CtuF eff           . (10) To find the EEPF at  tu s , we also apply the method of characteristics and get from Eq. (7): )11(,)1(2 )1(2 1 0 1 0 1/01 21 )2( )1(4 2 2 2 2 3 exp),(                                   t s s ts txx e u u e u uA t AtuF e where   , and esdd man /2 0 2 1   . If the EEPF at  tu s is Maxwellian, it follows from Eq. (11) the following expression for the EEPF at  tu s : Normalized EEPF for t = 0 (a) and )/(1.0 t (b); ad=50 nm, ne=10 9 сm -3 and different dust densities: nd =5.0 10 7 сm -3 (solid curve), 3.0 10 7 сm -3 (dashed curve ), 10 7 сm -3 (dotted curve). For  ts  , the EEPF is Maxwellian with Теff =2 еВ for t=0. Here, )/(1.0   . The same for nd =0 (c) and different af- terglow times: t = 0 (dash-dotted curve); 0.1 )/( (dotted curve); 0.3 )/( (dashed curve); 0.5 )/( (solid curve) a b c 182 ISSN 1562-6016. ВАНТ. 2016. №6(106) . )2( )1(4 2 2 2 2 3 exp),( )1(2 )1(2 1 0 1 0 1/01 1                                    t s s ts eff t e u u e u T uet AtuF (12) Using Eqs. (10) and (12), the EEPF was calculated for different dust densities (see Figs.a,b). The case nd =0 was also considered (Figure c). One can see in Figure that the EEPFs for  ts  in a dusty plasma differ essentially from those in a dust- free plasma. With an increase of dust density, the differ- ence on Maxwellian distribution in the region increases which is accompanied by a decrease of a number of electrons at large energies (  ts  ) and their increase at small energies (  ts  ). CONCLUSIONS Thus, we have shown that the EEPF in dusty glow and afterglow plasmas can be described analytically. The results of analytical studies presented here are in a good agreement with numerical and experimental re- sults on dusty plasma of previous authors. It has been shown that dust particles affect essentially the EEPF in glow and afterglow plasmas, decreasing the number of electrons at energies larger than the dust surface poten- tial, while increasing their number at energies smaller than the dust surface potential. ACKNOWLEDGEMENTS This work was supported by the State Fund for Fun- damental Research of Ukraine. REFERENCES 1. A. Bouchoule. Dusty Plasmas: Physics, Chemistry, and Technological Impacts in Plasma Processing. New York: “Wiley”. 1999. 2. S.V. Vladimirov and K. Ostrikov // Phys. Rep. 2004, v. 393, p. 175. 3. I. Denysenko, M.Y. Yu, K. Ostrikov, N.A. Azarenkov, and L. Stenflo // Phys. Plasmas. 2004, v. 11, p. 4959. 4. I. Denysenko, K. Ostrikov, M.Y. Yu, and N.A. Azarenkov // Phys. Rev. E. 2006, v. 74, p. 036402. 5. I. Denysenko, M.Y. Yu, L. Stenflo, S. Xu // Phys. Rev. E. 2005, v. 72, p. 016405. 6. L.M. Biberman, V.S. Vorobev, and I.T. Yakubov. Kinetics of Nonequilibrium Low-Temperature Plasma. Moscow: “Nauka”, 1982. 7. I.B. Denysenko, H. Kersten, and N.A. Azarenkov // Phys. Rev. E. 2015, v. 92, p. 033102. 8. I.B. Denysenko, H. Kersten, and N.A. Azarenkov // Phys. Plasmas. 2016, v. 23, p. 053704. 9. L. Elsgolts. Differential equations and the calculus of variations. Moscow: “Mir”, 1977. Article received 19.10.2016 ВЛИЯНИЕ ПЫЛЕВЫХ ЧАСТИЦ НА РАСПРЕДЕЛЕНИЕ ЭЛЕКТРОНОВ ПО ЭНЕРГИИ В ПЛАЗМЕ В РЕЖИМАХ СВЕЧЕНИЯ И ПОСЛЕСВЕЧЕНИЯ И.Б. Денисенко, Н.А. Азаренков, С. Ивко, Г. Бурмака, А. Глазков Из однородного уравнения Больцмана получены аналитические выражения для функции распределения электронов по энергии (ФРЭЭ) в пылевой плазме в режимах свечения и послесвечения. Для расчёта ФРЭЭ в режиме свечения при больших электронных энергиях применён квазиклассический подход. Для плазмы в режиме послесвечения аналитические выражения получены в предположении, что потери энергии электро- нов происходят в основном за счёт упругих электрон-нейтральных столкновений и благодаря осаждению электронов на пылевые частицы. Проанализировано влияние пылевых частиц на ФРЭЭ. ВПЛИВ ПИЛОВИХ ЧАСТИНОК НА РОЗПОДІЛ ЕЛЕКТРОНІВ ЗА ЕНЕРГІЄЮ В ПЛАЗМІ В РЕЖИМАХ СВІТІННЯ ТА ПІСЛЯСВІТІННЯ І.Б. Денисенко, М.О. Азарєнков, С. Івко, Г. Бурмака, А. Глазков З однорідного рівняння Больцмана отримано аналітичні вирази для функції розподілу електронів за енер- гією (ФРЕЕ) в запорошеної плазмi в режимах світіння та післясвітіння. Для розрахунку ФРЕЕ в режимі сві- тіння при великих електронних енергіях застосовано квазікласичний підхід. Для плазми в режимі післясві- тіння аналітичні вирази отримані в припущенні, що втрати енергії електронів відбуваються в основному за рахунок пружних електрон-нейтральних зіткнень та завдяки осадженню електронів на пилові частинки. Проаналізовано вплив пилових частинок на ФРЕЕ. http://scitation.aip.org/search?value1=I.+B.+Denysenko&option1=author&option912=resultCategory&value912=ResearchPublicationContent http://scitation.aip.org/search?value1=H.+Kersten&option1=author&option912=resultCategory&value912=ResearchPublicationContent http://scitation.aip.org/search?value1=N.+A.+Azarenkov&option1=author&option912=resultCategory&value912=ResearchPublicationContent https://archive.org/search.php?query=creator%3A%22L.+Elsgolts%22