Waves and solitons in complex plasma

and the MPE - UoL team

D. SamsonovThe University of Liverpool, Liverpool, UK

Complex plasmas in basics science

- linear and nonlinear waves- solitons - Mach cones (wakes)- shock waves - phase transitions- transport properties- nonlinear phenomena- model systems

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)

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

Data analysis

• particle identification

• particle tracking - yields velocity

• Voronoi analysis - number density

• averaging in bins - kinetic temperature

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

Phase states• solid: hexagonal crystal lattice

long range correlation

• liquid: some order

short range correlation

• gas: grains move fast

grain position are uncorrelated

Linear waves

Wave modes in a monolayer lattice:

Compressional (longitudinal) - acoustic

Shear (transverse) - acoustic

Vertical (transverse) - optical

Lattice waves

• phonon spectra• short wavelength - anisitropic• long wavelength - isotropic• compressional mode• shear mode• wave polarization longitudinal transverse mixedPRE 68, 035401, (2003)

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

Vertical wave packets

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)

Solitons

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)

Shock waves

Number density Kinetic temperature

Flow velocity Defect density

Experiment

Molecular dynamicssimulation

Shock (velocity vector map)Shock (velocity vector map)

Space experiments

• PKE-Nefedov

• PKE-3

• PKE-3+

• PKE-4

• PKE-….

Role of Gravity

Observation on Earth Observation under µg

Side view of a complex plasma

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)

PK4 experiment

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

Summary

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