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Waves and solitons in complex plasma

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

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Waves and solitons in complex plasma

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  1. Waves and solitons in complex plasma D. Samsonov The University of Liverpool, Liverpool, UK and the MPE - UoL team

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

  3. 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 • dynamicscan 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.

  4. 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

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

  6. 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

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

  8. Linear waves Wave modes in a monolayer lattice: Compressional (longitudinal) - acoustic Shear (transverse) - acoustic Vertical (transverse) - optical

  9. Lattice waves • phonon spectra • short wavelength - • anisitropic • long wavelength - • isotropic • compressional mode • shear mode • wave polarization • longitudinal • transverse • mixed PRE 68, 035401, (2003)

  10. 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)

  11. Vertical wave packets

  12. 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)

  13. Solitons

  14. 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)

  15. Shock waves

  16. Number density Kinetic temperature Flow velocity Defect density

  17. Shock (velocity vector map) Experiment Molecular dynamics simulation

  18. Space experiments • PKE-Nefedov • PKE-3 • PKE-3+ • PKE-4 • PKE-….

  19. Role of Gravity Side view of a complex plasma Observation on Earth Observation under µg

  20. 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)

  21. PK4 experiment

  22. 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

  23. Summary • complex plasmasmodel real systems • at the kinetic level (basic physics) • dynamics can be studied • linear waves • solitons • shocks • other dynamic phenomena

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