dynamic phenomena in complex plasmas n.f. cramer, s.v. vladimirov, a.a. samarian and b.w. james
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The University of Sydney. Dynamic Phenomena in Complex Plasmas N.F. Cramer, S.V. Vladimirov, A.A. Samarian and B.W. James School of Physics, University of Sydney, Australia. Dusty Plasmas at the University of Sydney. N. Cramer, S. Vladimirov, S. Maiorov (Theoretical Physics): - PowerPoint PPT PresentationTRANSCRIPT
Dynamic Phenomena in Complex Plasmas
N.F. Cramer, S.V. Vladimirov, A.A. Samarian and B.W. James
School of Physics, University of Sydney,Australia
The University of Sydney
N. Cramer, S. Vladimirov, S. Maiorov (Theoretical Physics):
Theory of Laboratory and Astrophysical Dusty Plasmas
B. James, A. Samarian, F. Cheung, W. Tsang (Applied and Plasma Physics):
Dusty Plasma Experiments
M. Wardle (Research Centre for Theoretical Astrophysics):
Charged Dust in Interstellar Clouds
Collaborators: N. Prior, O. Vaulina, O. Ishihara, V. Tsytovich,
F. Verheest, J. Sakai, M. Hellberg.
Dusty Plasmas at the University of Sydney
Dynamic Phenomena: Self-excited motionsOscillationsWavesVortex motions
Rotation of Fine Dust Clusters in Axial Magnetic Field
Laser Excited Oscillations in Vertically Aligned Structures
Dust Grains as Diagnostic Tool for Sheath Measurement in RF-Discharge Plasma
Potential energy of a dust grain with variable (solid lines) and constant charge (dashed lines) in the plasma sheath
Dynamics of Single Particle
Charging dynamics of the macroparticle of mg=105mp with and without an ion flow.The time step is =3.410-10s.Total simulation time is t0=190 and =6.5 x 10-8s.The asymptotic charge is
(a) Z =842 in the absence of the ion flow, M2=0(b) Z=1067 for M2=0.6 and(c) Z=1146 for M2=2.4
Contour plots of the ion density, for three values of the speed of the ion flow (one is subsonic with M2=0.6, and two supersonic, with M2=1.2 and M2=2.4).
A strong ion focus is formed at the distance of a fraction of the electron Debye length behind the dust grain
Instabilities of Dust Particle Arrangements
(Presentation of S Vladimirov et al.)
Rotation of Dust Coulomb Clusters in Axial Magnetic Field
(Presentation of Cheung et al.)
Laser Excited Oscillations in Vertically Aligned Structures
(Poster of Prior et al.)
Dynamics of Few Particles
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Laser Driven Oscillations of Few Particles Structures (Poster of Prior et al.)
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Instability of a string of 3 particles (paper of Vladimirov)
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Rotational motion
Various kinds of dust grain self-excited motion have been observed :
Vertical oscillations in mono-layer dust structure,
Complex wave motions in multi-layer structures,
Vortex motion caused by an introduction of an additional electrode,
Rotation and oscillation in non symmetrical electrode configurations.
Dynamics of Many Interacting Particles
Vibrational Modes of dust grain arrays
Vibrations in simple versions of lattices of dust grains embedded in the sheath region near a horizontal electrode. Understanding the modes provide useful diagnostics and aid in analysing critical phenomena and phase transitions in such systems
Horizontal vibrations of dust grains within one layer lead to acoustic-type modes. Vertical vibrations of dust grains in the layer lead to optical-mode-like dispersive waves
(Vladimirov, Shevchenko, and Cramer, 1997-1998)
Vibrations of a one-dimensional horizontal chain of grains of equal masses M and constant charge Q
For a mono-layer structure, the dust particles begin to oscillate spontaneously in the vertical direction when the pressure is decreased below a critical value.
Vertical Oscillation
30 mTorr and 100 W
30 mTorr and 35 W
30 mTorr and 15 W
The amplitude of the oscillation is several millimetres and the frequency is greater than 10Hz. When the rf input power is decreased, the amplitude increases.
For pressures below 35mTorr, the amplitude increases dramatically. This increase is greater for lower rf powers.
Vertical Oscillation
0
0,2
0,4
0,6
0,8
1
10 15 20 25 30 35 40
Pressure (mTorr)
Am
p (
mm
)
P=20 W
P=35 W
P=50 W
P=65 W
P=80 W
P=100 W
P=120 W
Carbon Particles (2.1±0.1m in diameter)
Second, consider two vertically ordered one-dimensional horizontal chains of grains with constant charges
ion flow
negatively charged electrode
The effect of the wake behind each grain in the Mach cone (Vladimirov and Nambu, 1995; Vladimirov and Ishihara 1996-
1998)
-----------> ion
-----------> flow
-----------> to the
----------->electrode
----------->
e
l e
c
t r
o d
e
There are two modes of oscillations:
Modes of vibrations
12
0
M
4Q2
Mr03
1 r0
D
exp
r0
D
sin2 kr0
2
22
0 1 2
M
4Q2
Mr03
1 r0
D
exp
r0
D
sin2 kr0
2
Modes of a chain of rod-like particles
Longitudinal compressive waves in 3-D structure (side)
We observed that density waves which travel downwards with a wavelength l=3mm and a period T=4x10-2s, were generated by decreasing the input power or pressure, and by increasing the number of dust particles in the structure
dp= 6.13 m,
P= 60 W, p= 30 mTorr
1sec1sec 2sec2sec
3sec3sec
Heartbeat Oscillation & Surface Waves
Wav
elen
gth
=6
mm
Vel
ocit
y v=
1.5m
s-1
0
6
0
5
PeaksPeaks
0.02
sec
0
.04s
ec
0.0
6sec
0
.08s
ec
1sec
2se
c
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Surface Waves
Wavelength =6mmVelocity v=1.5ms-1
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Void surface waves
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Rotational Motion
Illustration of Dust Vortex
Pin Electrode
(Top view)
Powered electrode
Groundedelectrode
DustVortex
Pin electrode
Side View Top View
Groundedelectrode
Pin electrode
Dust Vortex
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Vortex Motion