Transcript Slide 1
Waves and solitons in complex plasma D. Samsonov The University of Liverpool, Liverpool, UK and the MPE - UoL team 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 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. 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 Data analysis • • • • particle identification particle tracking - yields velocity Voronoi analysis - number density averaging in bins - kinetic temperature 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 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 mixed PRE 68, 035401, (2003) Dust-thermal waves • analogous to sound waves in gases • due to pressure term • dominates at high temperature • vDT=(gkBT/md)1/2 • g=2 in 2D case • g=5/3 in 3D case PRL 94, 045001, (2005) 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 Shock (velocity vector map) Experiment Molecular dynamics simulation Space experiments • PKE-Nefedov • PKE-3 • PKE-3+ • PKE-4 • PKE-…. Role of Gravity Side view of a complex plasma Observation on Earth Observation under µg 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