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