Dynamics of the modulated electron beam in the inhomogeneous plasma barrier: one-dimentional simulation using PIC method

Evolution of the modulated electron beam moving through the plasma barrier was studied via computer simulation using PIC method. Inhomogeneous plasma barrier with parameters corresponding to experimental conditions [1-2] was studied. Dependencies of the maximal signal amplitude and coordinate of thi...

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Published in:Вопросы атомной науки и техники
Date:2008
Main Authors: Anisimov, I.O., Soloviova, M.J.
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Language:English
Published: Національний науковий центр «Харківський фізико-технічний інститут» НАН України 2008
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Cite this:Dynamics of the modulated electron beam in the inhomogeneous plasma barrier: one-dimentional simulation using PIC method / I.O. Anisimov, M.J. Soloviova // Вопросы атомной науки и техники. — 2008. — № 4. — С. 209-213. — Бібліогр.: 12 назв. — англ.

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Digital Library of Periodicals of National Academy of Sciences of Ukraine
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spelling Anisimov, I.O.
Soloviova, M.J.
2017-01-04T20:42:51Z
2017-01-04T20:42:51Z
2008
Dynamics of the modulated electron beam in the inhomogeneous plasma barrier: one-dimentional simulation using PIC method / I.O. Anisimov, M.J. Soloviova // Вопросы атомной науки и техники. — 2008. — № 4. — С. 209-213. — Бібліогр.: 12 назв. — англ.
1562-6016
https://nasplib.isofts.kiev.ua/handle/123456789/110592
PACS: 52.35Mw, 52.40Mj
Evolution of the modulated electron beam moving through the plasma barrier was studied via computer simulation using PIC method. Inhomogeneous plasma barrier with parameters corresponding to experimental conditions [1-2] was studied. Dependencies of the maximal signal amplitude and coordinate of this maximum at the modulation frequency upon the initial beam modulation depth were obtained. Simulation results were compared with experimental results and outcomes of the previous simulations.
Досліджено еволюцію модульованого електронного пучка в плазмовому бар’єрі шляхом комп’ютерного моделювання методом крупних частинок. Розглядається неоднорідний плазмовий бар’єр, що відповідає умовам лабораторного експерименту. Отримано залежності максимального значення амплітуди сигналу на частоті модуляції та положення даного максимуму від початкової глибини модуляції. Результати моделювання співставлено з експериментальними даними та результатами попередніх моделювань.
Исследуется эволюция модулированного электронного пучка в плазменном барьере с помощью компьютерного моделирования методом крупных частиц. Рассматривается неоднородный плазменный барьер, соответствующий условиям лабораторного эксперимента. Получены зависимости максимальной амплитуды сигнала на частоте модуляции и положения данного максимума от начальной глубины модуляции. Результаты моделирования сопоставлены с экспериментальными данными и результатами предшествующих моделирований.
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
Вопросы атомной науки и техники
Нелинейные процессы в плазменных средах
Dynamics of the modulated electron beam in the inhomogeneous plasma barrier: one-dimentional simulation using PIC method
Динаміка модульованого електронного пучка в неоднорідному плазмовому бар’єрі: одновимірне моделювання методом частинок
Динамика модулированного электронного пучка в неоднородном плазменном барьере: одномерное моделирование методом частиц
Article
published earlier
institution Digital Library of Periodicals of National Academy of Sciences of Ukraine
collection DSpace DC
title Dynamics of the modulated electron beam in the inhomogeneous plasma barrier: one-dimentional simulation using PIC method
spellingShingle Dynamics of the modulated electron beam in the inhomogeneous plasma barrier: one-dimentional simulation using PIC method
Anisimov, I.O.
Soloviova, M.J.
Нелинейные процессы в плазменных средах
title_short Dynamics of the modulated electron beam in the inhomogeneous plasma barrier: one-dimentional simulation using PIC method
title_full Dynamics of the modulated electron beam in the inhomogeneous plasma barrier: one-dimentional simulation using PIC method
title_fullStr Dynamics of the modulated electron beam in the inhomogeneous plasma barrier: one-dimentional simulation using PIC method
title_full_unstemmed Dynamics of the modulated electron beam in the inhomogeneous plasma barrier: one-dimentional simulation using PIC method
title_sort dynamics of the modulated electron beam in the inhomogeneous plasma barrier: one-dimentional simulation using pic method
author Anisimov, I.O.
Soloviova, M.J.
author_facet Anisimov, I.O.
Soloviova, M.J.
topic Нелинейные процессы в плазменных средах
topic_facet Нелинейные процессы в плазменных средах
publishDate 2008
language English
container_title Вопросы атомной науки и техники
publisher Національний науковий центр «Харківський фізико-технічний інститут» НАН України
format Article
title_alt Динаміка модульованого електронного пучка в неоднорідному плазмовому бар’єрі: одновимірне моделювання методом частинок
Динамика модулированного электронного пучка в неоднородном плазменном барьере: одномерное моделирование методом частиц
description Evolution of the modulated electron beam moving through the plasma barrier was studied via computer simulation using PIC method. Inhomogeneous plasma barrier with parameters corresponding to experimental conditions [1-2] was studied. Dependencies of the maximal signal amplitude and coordinate of this maximum at the modulation frequency upon the initial beam modulation depth were obtained. Simulation results were compared with experimental results and outcomes of the previous simulations. Досліджено еволюцію модульованого електронного пучка в плазмовому бар’єрі шляхом комп’ютерного моделювання методом крупних частинок. Розглядається неоднорідний плазмовий бар’єр, що відповідає умовам лабораторного експерименту. Отримано залежності максимального значення амплітуди сигналу на частоті модуляції та положення даного максимуму від початкової глибини модуляції. Результати моделювання співставлено з експериментальними даними та результатами попередніх моделювань. Исследуется эволюция модулированного электронного пучка в плазменном барьере с помощью компьютерного моделирования методом крупных частиц. Рассматривается неоднородный плазменный барьер, соответствующий условиям лабораторного эксперимента. Получены зависимости максимальной амплитуды сигнала на частоте модуляции и положения данного максимума от начальной глубины модуляции. Результаты моделирования сопоставлены с экспериментальными данными и результатами предшествующих моделирований.
issn 1562-6016
url https://nasplib.isofts.kiev.ua/handle/123456789/110592
citation_txt Dynamics of the modulated electron beam in the inhomogeneous plasma barrier: one-dimentional simulation using PIC method / I.O. Anisimov, M.J. Soloviova // Вопросы атомной науки и техники. — 2008. — № 4. — С. 209-213. — Бібліогр.: 12 назв. — англ.
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fulltext НЕЛИНЕЙНЫЕ ПРОЦЕССЫ В ПЛАЗМЕННЫХ СРЕДАХ DYNAMICS OF THE MODULATED ELECTRON BEAM IN THE INHOMOGENEOUS PLASMA BARRIER: ONE-DIMENTIONAL SIMULATION USING PIC METHOD I.O. Anisimov, M.J. Soloviova Taras Shevchenko National University of Kyiv, Radio Physics Faculty, Kyiv, Ukraine E-mail: ioa@univ.kiev.ua Evolution of the modulated electron beam moving through the plasma barrier was studied via computer simula- tion using PIC method. Inhomogeneous plasma barrier with parameters corresponding to experimental conditions [1-2] was studied. Dependencies of the maximal signal amplitude and coordinate of this maximum at the modulation frequency upon the initial beam modulation depth were obtained. Simulation results were compared with experi- mental results and outcomes of the previous simulations. PACS: 52.35Mw, 52.40Mj 1. INTRODUCTION Problem of the modulated electron beam’s dynamics in plasma is of interest in various branches of plasma electronics such as electron beams’ using as emitters of electromagnetic waves in ionosphere [3-4], transillumi- nation of the plasma barriers for electromagnetic waves using electron beams [1-2, 5], inhomogeneous plasma diagnostics via transition radiation of electron beams and electron bunches [6] etc. ___________________________________________________________ ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 2008. № 4. Серия: Плазменная электроника и новые методы ускорения (6), с.209-213. 209 Evolution of the modulated electron beam in super- critical plasma barrier was studied experimentally in [2,7]. It was found out that signal at the modulation fre- quency reached its maximum inside the barrier, and magnitude of this maximum was directly proportional to the initial beam modulation depth. These results were explained in [8] by the concurrence between non- resonant (signal) and resonant (noise) modes of the beam-plasma system. But calculations presented in [8] correspond to the initial problem, whereas results of experiments [2, 7] correspond to the boundary problem. Consequently it was impossible to compare results of experiment and simulation. Evolution of the linear space-charge waves (SCW) of electron beam in the barrier with parabolic plasma density profile was studied theoretically in [2]. Effect of mutual transformation of SCW in the inhomogeneous plasma was obtained. In our previous works [9-10] evolution of the modu- lated electron beam in plasma for the initial-boundary problem was studied via computer simulation using PIC method [11-12]. But homogeneous plasma barrier in [9- 10] doesn’t correspond to the experimental one that is close to Gaussian shape [1-2, 7]. In this paper dynamics of the modulated electron beam moving through the barrier with Gaussian plasma density profile is studied via computer simulation using PIC method. Initial-boundary problem is solved, and results obtained are compared with results of experi- ments and previous simulations. 2. MODEL DESCRIPTION, SIMULATION METHOD AND PARAMETERS Warm isotropic collisionless plasma with initial Gaussian density profile is studied. Simulation is carried out via particle-in-cell method using modified program package PDP1 [11-12]. 1D region between two electrodes is simulated. Inte- relectrode space is filled with fully ionized hydrogen plasma. Initial plasma density profile is obtained by the approximation of experimental axial plasma density profile [1-2, 7] by Gaussian function. So initial electron and ion plasma density is set as 2 0 0( ) exp 2m x xn x n n ⎡ ⎤−⎛ ⎞= + −⎢ ⎜ ⎟Δ⎝ ⎠⎢ ⎥⎣ ⎦ ⎥ , (1) where n0 is the plasma density for x→∞, n0 + nm is the peak plasma density inside the barrier at x=x0, and Δ is half-width of the plasma density profile. Simulation parameters are presented in table. Simulation parameters n0 5.5·1010 cm-3 nm 2.04·1011 cm-3 x0 10 cm Δ 3.87 cm Simulation region length 20 cm Plasma electrons' thermal velocity 6⋅107 cm/s Plasma ions' thermal velocity 2,33⋅106 cm/s Beam electrons velocity 2⋅109 cm/s Electron beam modulation frequency 2.77 GHz Electron beam modulation depth 0.01…0.3 with the step 0.01 Simulation time step 10-13 s Electron beam is injected into plasma barrier from the left electrode. It moves to the right one. Electrodes absorb both plasma and beam particles. Initially electron beam is density-modulated: 0( ) (1 cos )t m tρ = ρ + ω , (2) where m is the modulation depth. Modulation frequency was selected in the range ωp(n0)<ω<ωp(n0+nm), where ωp(n) is electron plasma frequency corresponding to the plasma density n. So two local plasma resonance regions are presented inside the barrier at the modulation frequency. The simulation was carried out during the time in- terval of approximately 200 electron plasma periods or 5 ion plasma periods. During this time electron beam reached the opposite electrode and quasi-stationary re- gime was settled. 3. SIMULATION RESULTS 210 3.1. SPATIAL EVOLUTION OF SPECTRA OF ELECTRON BEAM DENSITY AND ELECTRIC FIELD STRENGTH FOR SMALL INITIAL DEPTH OF THE BEAM MODULATION All dependencies demonstrated in this section corre- spond to the initial modulation depth m = 0.05. Space-time distributions of the beam electrons' den- sity and electric field strength were obtained from simu- lation. Than temporal fast Furrier transformation was carried out. Fig.1 demonstrates the spatial evolution of spectra of electron beam density (a) and electric field strength (b). Arrows mark the modulation frequency. One can see from Fig.1,a that only the modulation frequency is pre- sented nearby the injector in the spectra of the electron beam density. During the beam motion inside the barrier in the region of plasma density increase the beam ex- cites oscillations at the local plasma frequency accord- ing to Cherenkov mechanism. As long as plasma den- sity depends on coordinate, local plasma frequency change up to coordinate too (in Fig.1,b it is noticeable near the modulation frequency). For the given frequency Cherenkov resonance conditions are not satisfied along the beam trajectory after the vicinity of the first plasma resonance point. So electric field in this region is de- creased, but corresponding oscillations in the spectrum of beam modes remain (see bottom of Fig.1,a). Conse- quently oscillations with the wide band of frequencies are presented in the beam density spectrum along with the modulation frequency. During the beam motion inside the barrier in the re- gion of plasma density decrease the oscillations pre- sented in the beam density spectrum excite the intensive electric fields in corresponding regions of local plasma resonance (top of Fig.1,b). At the same time the modulation of the beam at corresponding frequencies is increased (top of Fig.1,b). The largest length of resonant beam-plasma interac- tion is obtained near the maximum of plasma density, and this length is decreased at the periphery. Therefore maximal growth of the electric field of characteristic oscillations is observed in the region of maximal plasma density (Fig.1,b). Signal at the modulation frequency is noticeable at the whole simulation region both in spectra of electron beam density perturbation and electric field strength (Fig.1,a,b). Fig.2 presents the spatial evolution of spectra of electron beam density at the modulation frequency (a), electric field strength at the modulation frequency (b) and at the doubled modulation frequency (c). Similarly to the previous simulation [9-10], inside the barrier spectral amplitude of the electron beam den- sity at the modulation frequency reaches the maximum value (Fig.2,a). Spatial evolution of the electric field strength spectrum at the modulation frequency (fig.2,b) doesn’t demonstrate a maximum. Dependence of the field amplitude at the modulation frequency on coordi- nate contains a lot of fluctuations with considerable am- plitudes. a b Fig.1. Spatial evolution of spectra of electron beam density (a) and electric field strength (b). Arrows mark the signal modulation frequency The largest values of the field at the modulation fre- quency are reached in the regions of local plasma reso- nance at the edges of the barrier. High level of fluctua- tions is caused by presence of the wide-band oscillations in the electron beam spectrum. These fluctuations arise according to the mechanism of polarization beam- plasma instability (part of them are excited according to Cherenkov mechanism in local plasma resonance region as it was mentioned above). These fluctuations form the homogeneous gray background in the left side of Fig.1,b bounded by the frequency of local plasma resonance. But at the doubled modulation frequency (Fig.2,c) there are no oscillations at the local plasma frequency as well as strong fluctuations. That’s why spatial de- pendence of the signal at this frequency has the clear maximum, and it‘s position coincides with the position of the maximum in Fig.2,a. Notice that only a weak local peak is presented at this point in Fig.2,b. a b c Fig.2. Spatial evolution of spectra of electron beam density at the modulation frequency (a), electric field strength at the modulation frequency (b) and at the doubled modulation frequency (c) The position of the signal maximum at the modula- tion frequency (Fig.2,a,c) corresponds to x ≈ 11 cm. It is situated in the region where amplitude of the electric field strength at resonant frequencies grows considerably (Fig.1,b). So concurrence between resonant modes and signal at the modulation frequency takes place. As a re- sult restriction of the signal amplitude occurs as it was described in [8]. But the shape of plasma barrier density profile determines the position where this effect takes place for the parameters of our simulation. Notice that for homogeneous plasma density in the barrier [8] this coordinate is determined by the start of non-linear stage of the beam-plasma instability for the resonant mode. 3.2. SPATIAL EVOLUTION OF SPECTRA OF ELECTRON BEAM DENSITY AND ELECTRIC FIELD STRENGTH FOR LARGE INITIAL DEPTH OF THE BEAM MODULATION All dependencies discussed in this section correspond to the initial modulation depth m=0.28. They were ob- tained in the same way as in the previous section. Spatial evolution of spectra of electron beam density and electric field strength doesn’t differ drastically from the case of small initial depth of the beam modulation. а b c Fig.3. Spatial evolution of spectra of electron beam density at the modulation frequency (a), electric field strength at the modulation frequency (b) and at the doubled modulation frequency (c) Just as in previous case maximal growth of the field of the characteristic oscillations is observed in the range of maximal plasma density – in the middle of the barrier. In contrast to the case of small initial beam modula- tion depth, position of the maximal amplitude of the signal at the modulation frequency doesn’t coincide with the region of the maximal growth of the field of characteristic oscillations (Fig.3,a). From comparison Fig.2,a,c and Fig.3,a,c one can conclude that in this case distance from injector to maximum of the signal ampli- tude at the modulation frequency is much smaller than in the case of small initial beam modulation depth. So maximum of the signal at the modulation frequency is reached due to the non-linear saturation of its instability. Furthermore in Fig.3,a,c oscillations of the signal ampli- tude at the modulation frequency are observed. These oscillations are not observed in the case of small initial beam modulation depth (compare with Fig.2,a,с). But similar oscillations take place for strong beams in the homogeneous supercritical plasma [10]. Spatial evolution of spectra of electric field strength at the modulation frequency (Fig.3,b) doesn’t demon- strate any local maximums (contrary to Fig.2,b). This effect can be explained both by considerable removal of this maximum to injector and by its closeness to the first region of the local plasma resonance. 211 212 3.3. INFLUENCE OF THE INITIAL BEAM MODULATION DEPTH ON THE MAXIMAL SIGNAL AMPLITUDE AT THE MODULATION FREQUENCY AND POSITION OF THIS MAXIMUM Fig.4 presents dependencies of maximal signal am- plitude (a) and coordinate of this maximum (b) at the modulation frequency upon the initial beam modulation depth. Two characteristic regions of the initial beam modulation depth can be marked out from Fig.4. а b Fig.4. The dependencies of maximal signal amplitude (a) and coordinate of this maximum (b) at the modula- tion frequency on the initial beam modulation depth For initial modulation depths m≤0.1 the signal maximal amplitude is reached due to the concurrence of the signal at the modulation frequency with the reso- nant modes. Electric field of the resonant modes traps beam electrons, and as a result modulation at the signal frequency is suppressed. These processes occur just after electron beam passing through the plasma density maximum. That’s why maximal signal position remains constant in this range of initial modulation depths (Fig.4,b). For initial modulation depths m≥0.1 formation of the signal amplitude maximum at the modulation fre- quency is caused by the non-linear saturation of insta- bility. As a result maximum amplitude of the signal becomes approximately constant (Fig.4,a), and its posi- tion gradually moves to the injector (Fig.4,b). CONCLUSIONS Evolution of the modulated electron beam moving through the inhomogeneous plasma barrier was studied via computer simulation for 1D model using PIC method. 1. Spectrum of characteristic oscillations of the beam-plasma system competitive with the signal at the modulation frequency varies in space and depends on the barrier shape. The amplitude of these oscillations rises steeply in the region of plasma density decrease along the beam trajectory. Upper harmonics of charac- teristic oscillations of the beam-plasma system are pre- sented in this region. 2. Concurrence between resonant modes and signal at the modulation frequency takes place for small initial modulation depths (m≤0.1). This effect moves to restriction of the signal amplitude at the modulation frequency, as it was observed earlier in case of homogeneous barriers [9-10]. But now the shape of plasma barrier density profile determines the position, where maximal signal amplitude at the modulation frequency is reached. 3. For large initial modulation depths (m≥0.1) the signal amplitude maximum at the modulation frequency is reached as a result of beam-plasma instability satura- tion at this frequency. Oscillations of the signal ampli- tude at the modulation frequency are observed. In gen- eral the beam dynamics doesn’t differ from the case of homogeneous barriers [9-10]. REFERENCES 1. I.A. Anisimov, S.M. Levitsky, O.V. Opanasenko, L.I. Romanyuk. Experimental observation of the plasma wave barrier transillumination via electron beam // JTPh. 1991, v.61, №3, p.59-63. 2. I.O. Anisimov, I.Yu. Kotlyarov, S.M. Levitsky, O.V. Opanasenko, D.B. Palets, L.I. Romanyuk. The investigation of the transillumination of the plasma barriers for electromagnetic waves using electron beams. 2. Evolution of the space charge waves in the barrier // Ukr. Fiz. Zhurn. 1996, v.41, №3, p.164-170. 3. M. Starodubtsev, C. Krafft, P. Thevenet, A. Kos- trov. Whistler wave emission by a modulated elec- tron beam through transition radiation // Physics of Plasmas. 1999, v.6, №5, p.1427-1434. 4. I.A. Anisimov, S.M. Levitsky. On the possibility of observation of transition radiation in active beam- plasma experiments in upper atmosphere and space // Fizika plazmy. 1994, v.20, №9, p.824-827 (in Russian) 5. I.A. Anisimov, S.M. Levitsky. Electromagnetic waves transfer through dense plasma layer via electron flow // JTPh. 1989, v.59, N.7, p.50-54 (in Russian) 6. I.O. Anisimov. Transition radiation of the modu- lated electron beam for diagnostics of plasma for- mations // Ukr. Fiz. Zhurn. 1996, v.41, №9, p.798- 801 (in Ukrainian). 7. I.O. Anisimov, N.O. Bojko, S.V. Dovbakh, D.B. Palets, L.I.Romanyuk. The influence of the initial modulation depth of the electron beam on its evolution in plasma // Ukr. Fiz. Zhurn. 2000, v.45, №11, p.1318-1323 (in Ukrainian) 8. I.O. Anisimov, S.V. Dovbakh, S.M. Levitsky, G.V. Lizunov, H.V. Podladchikova. Concurrence of modes in the signals' transport through the plasma wave barriers via electron beams // Kyiv University Bulletin. Radiophisics and Electronics. 2000, №2, p.10-17 (in Ukrainian). 9. I.O. Anisimov, M.J. Kiyanchuk. Evolution of the modulated electron beam in supercritical plasma: simulation of initial-boundary problem // Problems of Atomic Science and Technology. Series «Plasma electronics and new acceleration methods». 2006, №5, p.24-27. 11. Ch.K. Birdsall, A.B. Langdon // Plasma Physics, via Computer Simulation. McGraw-Hill Book Com- pany, 1985. 12. I.O. Anisimov, D.V. Sasyuk, T.V. Siversky. Modi- fied package PDP1 for beam-plasma systems’ simu- lation // Dynamical system modelling and stability investigation. Thesis of conference reports. Kyiv, 2003, p.257. 10. I.O. Anisimov, M.J. Kiyanchuk. Evolution of the modulated electron beam in plasma for different modes of beam-plasma turbulence // Ukr. Fiz. Zhurn. 2008, v.53, №4, p.382-388. Статья поступила в редакцию 08.05.2008 г. ДИНАМИКА МОДУЛИРОВАННОГО ЭЛЕКТРОННОГО ПУЧКА В НЕОДНОРОДНОМ ПЛАЗМЕННОМ БАРЬЕРЕ: ОДНОМЕРНОЕ МОДЕЛИРОВАНИЕ МЕТОДОМ ЧАСТИЦ И.А. Анисимов, М.И. Соловьёва Исследуется эволюция модулированного электронного пучка в плазменном барьере с помощью компьютерного моделирования методом крупных частиц. Рассматривается неоднородный плазменный барьер, соответствующий условиям лабораторного эксперимента. Получены зависимости максимальной амплитуды сигнала на частоте модуляции и положения данного максимума от начальной глубины модуляции. Результаты моделирования сопоставлены с экспериментальными данными и результатами предшествующих моделирований. ДИНАМІКА МОДУЛЬОВАНОГО ЕЛЕКТРОННОГО ПУЧКА В НЕОДНОРІДНОМУ ПЛАЗМОВОМУ БАР’ЄРІ: ОДНОВИМІРНЕ МОДЕЛЮВАННЯ МЕТОДОМ ЧАСТИНОК І.О. Анісімов, М.І. Соловйова Досліджено еволюцію модульованого електронного пучка в плазмовому бар’єрі шляхом комп’ютерного моделювання методом крупних частинок. Розглядається неоднорідний плазмовий бар’єр, що відповідає умовам лабораторного експерименту. Отримано залежності максимального значення амплітуди сигналу на частоті модуляції та положення даного максимуму від початкової глибини модуляції. Результати моделювання співставлено з експериментальними даними та результатами попередніх моделювань. 213 Simulation parameters