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![Page 1: Waves and solitons in complex plasma and the MPE - UoL team D. Samsonov The University of Liverpool, Liverpool, UK.](https://reader036.fdocuments.us/reader036/viewer/2022062407/56649e905503460f94b94eb1/html5/thumbnails/1.jpg)
Waves and solitons in complex plasma
and the MPE - UoL team
D. SamsonovThe University of Liverpool, Liverpool, UK
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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 plasmasMain features of complex plasmas
• low oscillation frequency (1 - 100Hz) due to high mass
• low damping rate (~1 - 100s-1) compared to colloids
• 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.
• large interparticle spacing (30µm - 1mm)
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Laboratory experiments (2D)• argon, 1-2 Pa, 1.5-2 sccm
• 2-100 W ccrf-discharge
• 8.9m 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 simulation3D 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 mixedPRE 68, 035401, (2003)
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Dust-thermal waves
PRL 94, 045001, (2005)
• analogous to sound
waves in gases• due to pressure term• dominates at high
temperature
• vDT=(kBT/md)1/2
• =2 in 2D case• =5/3 in 3D case
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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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Experiment
Molecular dynamicssimulation
Shock (velocity vector map)Shock (velocity vector map)
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Space experiments
• PKE-Nefedov
• PKE-3
• PKE-3+
• PKE-4
• PKE-….
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Role of Gravity
Observation on Earth Observation under µg
Side view of a complex plasma
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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
Q=1600-2200e
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