Waves and solitons in complex plasma

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Waves and solitons in complex plasma
D. Samsonov The University of Liverpool,
Liverpool, UK

• and the MPE - UoL team

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Complex plasmas in basics science
- linear and nonlinear waves - solitons - Mach
cones (wakes) - shock waves - phase
transitions - transport properties - nonlinear
phenomena - model systems
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Main features of complex plasmas

• low oscillation frequency (1 - 100Hz) due to high
  mass

• low damping rate (1 - 100s-1) compared to
  colloids

• large interparticle spacing (30µm - 1mm)

• can be in gaseous, liquid or crystalline states

• dynamics can be studied at the kinetic level
  with a video camera (or observed by
  the naked eye)
• can be used as a macroscopic model system for
  studying waves, shocks, solitons, etc.

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Laboratory experiments (2D)

• argon, 1-2 Pa, 1.5-2 sccm
• 2-100 W ccrf-discharge
• 8.9mm plastic microspheres
• monolayer hexagonal
• lattice
• 0.2-1mm grain separation
• green laser illumination
• top view video camera

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Data analysis

• particle identification
• particle tracking - yields velocity
• Voronoi analysis - number density
• averaging in bins - kinetic temperature

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3D molecular dynamics simulation

• Particles interact via Yukawa potential
• Particles are strongly confined vertically
• Particles are weakly confined horizontally
• No plasma, damping due to neutral friction
• Equations of motion are solved
• Particles are seeded randomly
• Code is run to equilibrate the resulting
  monolayer
• Excitation is applied

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Phase states

• solid hexagonal crystal lattice
• long range correlation
• liquid some order
• short range correlation
• gas grains move fast
• grain position are uncorrelated

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Linear waves

• Wave modes in a monolayer lattice
• Compressional (longitudinal) - acoustic
• Shear (transverse) - acoustic
• Vertical (transverse) - optical

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Lattice waves

• phonon spectra
• short wavelength -
• anisitropic
• long wavelength -
• isotropic
• compressional mode
• shear mode
• wave polarization
• longitudinal
• transverse
• mixed

PRE 68, 035401, (2003)
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Dust-thermal waves

• analogous to sound
• waves in gases
• due to pressure term
• dominates at high
• temperature
• vDT(gkBT/md)1/2
• g2 in 2D case
• g5/3 in 3D case

PRL 94, 045001, (2005)
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Vertical wave packets
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Vertical wave packets

• top view
• stripes move left
• packet moves right
• inverse optical
• dispersion
• Vgr 4 mm/s
• Vph -290 mm/s
• CDL 35 mm/s

PRE 71, 026410, (2005)
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Solitons
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Solitons

• localized (solitary) wave
• soliton parameter
• AL2 const
• damping due to friction
• dissipative solitons
• described by the KdV
• equation
• weak nonlinearity
• weak dispersion
• multiple solitons
• are possible

PRL 88, 095004, (2002)
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Shock waves
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Number density
Kinetic temperature
Flow velocity
Defect density
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Shock (velocity vector map)
Experiment
Molecular dynamics simulation
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Space experiments

• PKE-Nefedov
• PKE-3
• PKE-3
• PKE-4
• PKE-.

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Role of Gravity
Side view of a complex plasma
Observation on Earth
Observation under µg
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Waves in a 3D complex plasma
Electrode voltage modulation excites waves
frequency is varied dispersion is measured fit
with DAW and DLW
theory grain charge is
determined Q1600-2200e
Phys. Plasmas 10, 1, (2003)
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PK4 experiment
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Plans for future experiments

• obtain large monolayer crystals
• reduce damping rate
• linear waves in binary mixtures
• vertical waves
• solitons and their interaction
• shocks and their interaction

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Summary

• complex plasmas model real systems
• at the kinetic level (basic physics)
• dynamics can be studied
• linear waves
• solitons
• shocks
• other dynamic phenomena