Dust particle charging in sheath
The charging and the screening of spherical dust particles in sheaths near the wall were studied using computer simulation. The three-dimensional PIC/MCC method and molecular dynamics method were applied to describe plasma particles motion and interaction with macroscopic dust grain. Calculations we...
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irk-123456789-819532015-05-23T03:01:54Z Dust particle charging in sheath Gavrysh, G.O. Kravchenko, O.Yu. Lisitchenko, T.E. Низкотемпературная плазма и плазменные технологии The charging and the screening of spherical dust particles in sheaths near the wall were studied using computer simulation. The three-dimensional PIC/MCC method and molecular dynamics method were applied to describe plasma particles motion and interaction with macroscopic dust grain. Calculations were carried out at different neutral gas pressures and wall potentials. Values of the charge of the dust particles and spatial distributions of plasma parameters are obtained by modelling. The results have shown that the charge of the dust particles in the sheath, as well as the spatial distribution of the ions and electrons near the dust particles, depend strongly on the wall potential. It is shown that for large negative values of the wall potential the negative charge of a dust particle decreases due to the decline of the electron density in its vicinity. In addition, the flow of energy of the ions on the surface of dust particles is increased due to better focusing effect of the dust particle field on ions. Зарядка и экранирование сферических пылевых частиц в приэлектродных слоях вблизи стенки были изучены с помощью компьютерного моделирования. Трехмерный PIC/MCC-метод и метод молекулярной динамики были применены для описания движения частиц плазмы и взаимодействия их с макроскопической пылинкой. Расчеты проводились при различных значениях давления нейтрального газа и потенциала стенки. Значения заряда пылевых частиц и пространственные распределения параметров плазмы получены при помощи моделирования. Результаты показали, что заряд пылевых частиц в приэлектродном слое, а также пространственные распределения ионов и электронов вблизи пылевых частиц сильно зависят от потенциала стенки. Показано, что при больших значениях потенциала стенки отрицательный заряд пылевой частицы уменьшается в связи с уменьшением плотности электронов в ее окрестности. Кроме того, поток энергии ионов на поверхность пылевой частицы увеличивается за счет лучшего фокусирующего действия поля пылевых частиц на ионы. Зарядка і екранування сферичних пилових частинок у приелектродних шарах поблизу стінки були вивчені за допомогою комп'ютерного моделювання. Тривимірний PIC/MCC-метод і метод молекулярної динаміки були застосовані для опису руху частинок плазми та взаємодії їх з макроскопічною пилинкою. Розрахунки проводились при різних значеннях тиску нейтрального газу і потенціалу стінки. Значення заряду пилових частинок і просторові розподіли параметрів плазми отримані за допомогою моделювання. Результати показали, що заряд пилових частинок у приелектродному шарі, а також просторові розподіли іонів і електронів поблизу пилових частинок сильно залежать від потенціалу стінки. Показано, що при великих значеннях потенціалу стінки негативний заряд пилової частинки зменшується в зв'язку зі зменшенням концентрації електронів поблизу неї. Крім того, потік енергії іонів на поверхню пилової частинки збільшується за рахунок кращої фокусуючої дії поля пилових частинок на іони. 2014 Article Dust particle charging in sheath / G.O. Gavrysh, O.Yu. Kravchenko, T.E. Lisitchenko // Вопросы атомной науки и техники. — 2014. — № 6. — С. 160-163. — Бібліогр.: 6 назв. — англ. 1562-6016 PACS: 52.27.Lw. http://dspace.nbuv.gov.ua/handle/123456789/81953 en Вопросы атомной науки и техники Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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Низкотемпературная плазма и плазменные технологии Низкотемпературная плазма и плазменные технологии |
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Низкотемпературная плазма и плазменные технологии Низкотемпературная плазма и плазменные технологии Gavrysh, G.O. Kravchenko, O.Yu. Lisitchenko, T.E. Dust particle charging in sheath Вопросы атомной науки и техники |
| description |
The charging and the screening of spherical dust particles in sheaths near the wall were studied using computer simulation. The three-dimensional PIC/MCC method and molecular dynamics method were applied to describe plasma particles motion and interaction with macroscopic dust grain. Calculations were carried out at different neutral gas pressures and wall potentials. Values of the charge of the dust particles and spatial distributions of plasma parameters are obtained by modelling. The results have shown that the charge of the dust particles in the sheath, as well as the spatial distribution of the ions and electrons near the dust particles, depend strongly on the wall potential. It is shown that for large negative values of the wall potential the negative charge of a dust particle decreases due to the decline of the electron density in its vicinity. In addition, the flow of energy of the ions on the surface of dust particles is increased due to better focusing effect of the dust particle field on ions. |
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Article |
| author |
Gavrysh, G.O. Kravchenko, O.Yu. Lisitchenko, T.E. |
| author_facet |
Gavrysh, G.O. Kravchenko, O.Yu. Lisitchenko, T.E. |
| author_sort |
Gavrysh, G.O. |
| title |
Dust particle charging in sheath |
| title_short |
Dust particle charging in sheath |
| title_full |
Dust particle charging in sheath |
| title_fullStr |
Dust particle charging in sheath |
| title_full_unstemmed |
Dust particle charging in sheath |
| title_sort |
dust particle charging in sheath |
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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2014 |
| topic_facet |
Низкотемпературная плазма и плазменные технологии |
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http://dspace.nbuv.gov.ua/handle/123456789/81953 |
| citation_txt |
Dust particle charging in sheath / G.O. Gavrysh, O.Yu. Kravchenko, T.E. Lisitchenko // Вопросы атомной науки и техники. — 2014. — № 6. — С. 160-163. — Бібліогр.: 6 назв. — англ. |
| series |
Вопросы атомной науки и техники |
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AT gavryshgo dustparticlecharginginsheath AT kravchenkooyu dustparticlecharginginsheath AT lisitchenkote dustparticlecharginginsheath |
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2025-07-06T07:44:48Z |
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2025-07-06T07:44:48Z |
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| fulltext |
ISSN 1562-6016. ВАНТ. 2014. №6(94) 163
DUST PARTICLE CHARGING IN SHEATH
G.O. Gavrysh, O. Yu. Kravchenko, T.E. Lisitchenko
Taras Shevchenko National University of Kyiv, Ukraine
E-mail: kay@univ.kiev.ua
The charging and the screening of spherical dust particles in sheaths near the wall were studied using computer
simulation. The three-dimensional PIC/MCC method and molecular dynamics method were applied to describe
plasma particles motion and interaction with macroscopic dust grain. Calculations were carried out at different
neutral gas pressures and wall potentials. Values of the charge of the dust particles and spatial distributions of
plasma parameters are obtained by modelling. The results have shown that the charge of the dust particles in the
sheath, as well as the spatial distribution of the ions and electrons near the dust particles, depend strongly on the
wall potential. It is shown that for large negative values of the wall potential the negative charge of a dust particle
decreases due to the decline of the electron density in its vicinity. In addition, the flow of energy of the ions on the
surface of dust particles is increased due to better focusing effect of the dust particle field on ions.
PACS: 52.27.Lw.
INTRODUCTION
The problem of the charging and screening of dust
particles immersed in plasma is one of the basic
problems of dusty-plasma physics. The grain charge,
together with the electric potential distribution around
the grain, determines electric interactions between dust
particles. These grain-grain interactions are responsible
for a number of collective phenomena, such as
formation of ordered (crystal-like) structures and phase
transitions. Various approximate models and PIC/MCC
computer simulations have been used previously to
calculate the particle charge [1-4]. These studies were
carried out for spherical dust particles immersed in
uniform equilibrium plasma. However, most of the
dusty plasma experiments were done in the sheath
region close to the wall in a gas discharge plasma. The
presence of the electric field and ion flow in the sheath
plays an important role in the dust particle charging.
Hereupon, the investigation of dust particle charging
and screening in sheath is an actual problem.
MODEL AND SIMULATION METHOD
We consider a spherical dust particle in the sheath,
which occurs at the plasma boundary with a flat
conductive wall. Wall potential w is given and does not
change over time. It is assumed that at the initial time
the dust particle is uncharged, the plasma consists of
electrons and ions and is homogeneous. Over time, the
sheath is formed near the wall, and the dust particle
acquires a certain charge qd. In our calculations the dust
particle radius was Rd=5 m, the distance of the dust
particles from the wall was L = 10
-4
m, the pressure of
the neutral gas was varied from 0…5 Torr. At the
sheath edge densities of plasma particles (electrons and
ions) were n0=10
17
m
-3
. Electron flow in this point is
assumed to be thermal, but the ion flow velocity is
assumed to have ion sound velocity. The mass of the
neutral gas atoms and ions was equal to hydrogen to
reduce computational time, but the elementary cross-
sections were equal to argon. The electron and ion
temperatures were assumed to be Te=1 eV and
Ti=0.03 eV
respectively. The length of the
computational area cube is L= 210
-4
m, that is much
greater than electron Debye length. The simulation time
is =510
-8
s that exceeds the time at which the ion flies
the length L .
The three-dimensional PIC/MCC method is applied
for solving this task [5]. In order to accurately resolve
close-range interactions between dust grains and plasma
particles, the PIC model has been combined with a
molecular dynamic MD algorithm. In the resulting
particle-particle particle-mesh (P3M) model, the long-
range interaction of the dust grains with charged
particles of the background plasma is treated according
to the PIC formalism. For particles which are closer to
the dust grain than a Debye length their interaction force
is computed according to a direct particle-particle MD
scheme using the exact electrostatic potential [6]. The
interaction between plasma particles and neutral gas
was simulated using Monte-Carlo method for describing
of elementary processes, such as elastic, excitation,
ionization, charge exchange processes. If an electron or
ion in its motion crossed the particle surface, it was
thought that it recombines and its charge is transferred
to the dust particle.
RESULTS
Simulations results were obtained for various wall
potentials w and neutral gas pressures p. Typical results
of the computer simulations are shown in Figs. 1-4.
Temporal dependences of a dust particle charge are
presented in Fig. 1. Fig. 1,a corresponds to the wall
potential w=–9 V, and Fig. 1,b corresponds to w= –16 V.
Different curves in the figures correspond to different
values of the gas pressure, indicated in the figure. As
can be seen in Fig. 1,a, charge of a dust particle
increases monotonically with time for all values of the
gas pressure and tends to some constant values. The
charge of dust particle is increased in magnitude with
increasing gas pressure.
In the case of w= –16 V, after the initial increase of
dust particle charge, there is a further reduction of it. In
addition, there is a non-monotonic dependence of the
charge on the gas pressure. Note, that the charge of a
dust particle in this case is much smaller in absolute
value than in the case of w=-9 V.
Fig. 2 demonstrates spatial distributions of ion (a)
and electron (b) density along a line that passes through
the center of the dust particle parallel to the axis y in
the case of the wall potential w=-9 V. Note, that dust
particle is located at the point y= 10
-4
m. The forming of
peaks is observed for the ion density behind the dust
particle towards the wall. Moreover, the peaks decrease
with increasing gas pressure. The formation of these
peaks occurs due to ion focusing by the field of the dust
particle and the formation of an ion cloud behind the
dust particle. In addition, the ion density minimum is
formed in the vicinity of the dust particle in all variants
of calculations.
0,0 4,0x10
-9
8,0x10
-9
-8000
-6000
-4000
-2000
0
q
d
/e
t, s
p=0
p=1 Torr
p=5 Torr
a
0,0 5,0x10
-9
1,0x10
-8
1,5x10
-8
-3000
-2000
-1000
0
q
d
/e
t, s
p=0
p=1 torr
p=5 Torr
b
Fig. 1. Temporal dependences of the dust particle
charge for case of w=-9 V
(a) and w=-16 V
(b) and
different gas pressures, represented on the figure
Fig. 2,b shows corresponding spatial distributions of
electron density along the specified direction. It can be
seen that near the wall (at y= 210
-4
m) the electrons are
practically absent. Additionally, maxima of the electron
density are much smaller than maxima of ion density
behind the dust particle. Therefore, a region of large
positive charge is formed behind the dust particle
towards the wall.
Fig. 3 shows the spatial distributions of the ion (a)
and the electron (b) densities in the case of the wall
potential w=-16 V. In these cases, the focusing of ions
is not observed behind the dust particle. The reasons for
this is that at the increasing negative wall potential ions
gain greater velocity and are less deflected when they
move in the field of the dust particle.
Feature of spatial electron distributions in these
cases is that between the dust particle and the wall
electrons are practically absent. This leads to a
substantial reduction of the electron current on the dust
particle, whereby negative charge of the dust particle
reduces greatly (see Fig. 1,b).
0,0 5,0x10
-5
1,0x10
-4
1,5x10
-4
2,0x10
-4
0
20
40
60
n
i
y, m
p=0
p=1 Torr
p=5 Torr
a
5,0x10
-5
1,0x10
-4
1,5x10
-4
2,0x10
-4
0
5
10
15
20
n
e
y, m
p=0
p=1 Torr
p=5 Torr
b
Fig. 2. Spatial distributions of ion density (a) and
electron density (b) along y-axis for w=-9 V and
different values of neutral gas pressures
Fig. 4 shows the spatial distributions of the electric
field potential along axes y for specified previously
cases. In the presented calculations for w=-9 V (see
Fig. 4,a) distributions of electric potential are almost
identical at different gas pressures. Near the dust
particle potential well is formed, due to a high negative
charge of the dust particle. In the case of w= –16 V
potential well is small in the vicinity of the dust
particles, since the charge of dust particles in these cases
is much smaller. However, in this case, the gas pressure
stronger influences on the spatial distributions of
electric potential. With increasing gas pressure the
thickness of the sheath (region of sharp change of the
potential) decreases and the electron density increases
near the dust particle. This leads to an increase of the
electron current on the surface of dust and to an increase
of its charge in magnitude.
We now analyse the energy flow to the dust particle
due to electron and ion fluxes to the surface. It is
assumed in our model that the kinetic energy of plasma
particles is transferred to dust particle entirely in
collisions.
0,0 5,0x10
-5
1,0x10
-4
1,5x10
-4
2,0x10
-4
0
5
10
15
20
n
i
y, m
p=0
p=5 Torr
a
0,0 5,0x10
-5
1,0x10
-4
1,5x10
-4
2,0x10
-4
0
5
10
15
20
25
n
e
y, m
p=0
p=5 Torr
b
Fig. 3. Spatial distributions of ion density (a) and
electron density (b) along y-axis for w= -16 V and
different values of neutral gas pressures
0,0 1,0x10
-4
2,0x10
-4
-10
-8
-6
-4
-2
0
w
, V
y, m
p=0
p=1 Torr
p=5 Torr
a
0,0 5,0x10
-5
1,0x10
-4
1,5x10
-4
2,0x10
-4
-15
-10
-5
0
, V
y, m
p=0
p=1 torr
p=5 torr
b
Fig. 4. Spatial distributions of electric potential along
y-axis for 9w V (a )and for 16w V (b)
Fig. 5,a shows time dependences of the energy flux
of ions to the surface of the dust particles in the absence
of neutral particles in the sheath (p=0) for two values of
the wall potential. It can be seen that with the increasing
of the negative wall potential, the energy flux of ions on
the dust particle is reduced. Similar dependences of ion
energy fluxes are shown in Fig. 5,b for the neutral gas
pressure p=5 Torr. The increasing of the ion energy
flow with a decrease of the negative potential of the
wall is observed in this case also. This result is
explained by the more effective focusing action of the
dust particle field on ions in the case of w=-9 V
0,0 4,0x10
-9
8,0x10
-9
0,0
2,0x10
11
4,0x10
11
6,0x10
11
i
t, s
w
=-9 V
w
=-16 V
a
0,00E+000 4,00E-009 8,00E-009
0,0
2,0x10
-9
4,0x10
-9
i
t,s
w
=-9 V
w
=-16 V
b
Fig. 5. Temporal dependences of the ion energy flow to
dust particle for case p=0 (a) and p=5 Torr (b) and
different wall potentials, represented in figure
Comparison of energy fluxes of ions at the same
potential wall, but different pressures, shows a decrease
of this flows with increasing pressure. The reason for
this is the influence of collisions between ions and
neutral atoms (elastic collisions and charge exchange
processes) on ion fluxes on the dust particle.
CONCLUSIONS
This paper covers the charging and screening of dust
particles in the sheath. The charges of dust grains and
spatial distributions of plasma particles around them
were obtained at different neutral gas pressures and wall
potentials. The formation of the ion clouds behind dust
particles owing to focusing of ion flows was observed at
low wall potentials. The dust particle charge decreases
in magnitude with increasing of negative wall potential.
Simulation results also showed the formation of the
potential minimum near the dust particle in case of low
wall potential.
The ion energy flows on dust particles in sheaths
were calculated. They increase with decreasing of gas
pressure due to the influence of ion - atom collisions on
the ion flux onto dust particles. It is also shown that the
ion energy flow increases with decreasing of the wall
negative potential, which is a consequence of improving
of the focusing action of the dust particle field.
REFERENCES
1. I.L. Semenov, A.G. Zagorodny, I.V. Krivtsun // Phys.
Plasmas. 2012, v. 9, p. 043703.
2. I.H. Hutchinson // Plasma Phys. Controlled Fusion.
2003, v. 45, p. 1477.
3. S.A. Khrapak, B.A. Klumov, and G.E. Morfill
// Phys. Rev. Lett. 2008, v. 100, p. 225003.
4. L. G. D’yachkov, O.F. Petrov, V.E. Fortov, Contrib.
// Plasma Phys. 2009, v. 49, p. 134-147.
5. C.K. Birdsall //IEEE Trans. Plasma Sci. 1999, v. 1,
p. 65-85.
6. G.O. Gavrysh, O.Yu. Kravchenko, T.E. Lisitchenko,
I. Koval // Problems of Atomic Science and Technology.
2012, № 1, p. 243-245.
Article received 23.10.2014
ЗАРЯДКА ПЫЛЕВОЙ ЧАСТИЦЫ В ПРИЭЛЕКТРОДНОМ ШАРЕ
Г.О. Гавриш, О.Ю. Кравченко, Т.Е. Лиситченко
Зарядка и экранирование сферических пылевых частиц в приэлектродных слоях вблизи стенки были
изучены с помощью компьютерного моделирования. Трехмерный PIC/MCC-метод и метод молекулярной
динамики были применены для описания движения частиц плазмы и взаимодействия их с
макроскопической пылинкой. Расчеты проводились при различных значениях давления нейтрального газа и
потенциала стенки. Значения заряда пылевых частиц и пространственные распределения параметров плазмы
получены при помощи моделирования. Результаты показали, что заряд пылевых частиц в приэлектродном
слое, а также пространственные распределения ионов и электронов вблизи пылевых частиц сильно зависят
от потенциала стенки. Показано, что при больших значениях потенциала стенки отрицательный заряд
пылевой частицы уменьшается в связи с уменьшением плотности электронов в ее окрестности. Кроме того,
поток энергии ионов на поверхность пылевой частицы увеличивается за счет лучшего фокусирующего
действия поля пылевых частиц на ионы.
ЗАРЯДКА ПИЛОВОЇ ЧАСТИНКИ В ПРИЕЛЕКТРОДНОМУ ШАРІ
Г.О. Гавриш, О.Ю. Кравченко, Т.Е. Лиситченко
Зарядка і екранування сферичних пилових частинок у приелектродних шарах поблизу стінки були
вивчені за допомогою комп'ютерного моделювання. Тривимірний PIC/MCC-метод і метод молекулярної
динаміки були застосовані для опису руху частинок плазми та взаємодії їх з макроскопічною пилинкою.
Розрахунки проводились при різних значеннях тиску нейтрального газу і потенціалу стінки. Значення заряду
пилових частинок і просторові розподіли параметрів плазми отримані за допомогою моделювання.
Результати показали, що заряд пилових частинок у приелектродному шарі, а також просторові розподіли
іонів і електронів поблизу пилових частинок сильно залежать від потенціалу стінки. Показано, що при
великих значеннях потенціалу стінки негативний заряд пилової частинки зменшується в зв'язку зі
зменшенням концентрації електронів поблизу неї. Крім того, потік енергії іонів на поверхню пилової
частинки збільшується за рахунок кращої фокусуючої дії поля пилових частинок на іони.
|