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Optically-Excited Waves in 3D Dusty Plasmas

Optically-Excited Waves in 3D Dusty Plasmas. John Goree The University of Iowa. plasma = electrons + ions. small particle of solid matter. absorbs electrons and ions. becomes negatively charged. Debye shielding. What is a dusty plasma?. Solar system Rings of Saturn Comet tails.

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Optically-Excited Waves in 3D Dusty Plasmas

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  1. Optically-Excited Waves in 3D Dusty Plasmas John Goree The University of Iowa

  2. plasma = electrons + ions small particle of solid matter • absorbs electrons and ions • becomes negatively charged • Debye shielding What is a dusty plasma?

  3. Solar system • Rings of Saturn • Comet tails • Manufacturing • Particle contamination • (Si wafer processing) • Nanomaterial synthesis • Fundamental science • Coulomb crystals • Waves Who cares about dusty plasmas?

  4. Forces Acting on a Particle Coulomb QE Gravity mg • Other forces: • Gas drag • Ion drag • Thermophoresis • Radiation Pressure

  5. electrode Equipotential contours electrode Without gravity, particles fill 3-D volume positive potential QE With gravity, particles sediment to high-field region Þ2-D layer mg electrode electrode Electrostatic trapping of particles

  6. polymer microspheres 8 mm diameter Particles • separation a» 0.5 mm • charge Q» - 104e

  7. Comparison to Colloidal Suspensions Same: • Coulomb repulsion • Crystals Different: • Dusty plasma has much lower damping rate Þ wave propagation is easier

  8. Experiments described in this talk • 2D physics: Ground-based • 3D physics: Flight

  9. triangular lattice with hexagonal symmetry 2D lattice Yukawa inter-particle potential

  10. Two modesin a lattice

  11. Dispersion relationsin 2D triangular lattice Q=0, Wang et al. PRL 2001

  12. Setup

  13. Scanning mirror scanning mirror Ar laser beam

  14. 4mm k Laser incident here Longitudinal wave f = 1.8 Hz

  15. = compression + shear 4mm Random particle motion No Laser! Nunomura et al. PRL 2002

  16. & sinusoidally-excited waves Phonon spectrum Nunomura et al. PRL 2002

  17. Machcones

  18. C = U Sin m U m Machconeangle

  19. Lateral wake Transverse Wake Ship’swake

  20. air plasma crystal m water Wake pattern is determined bydispersion relation Mach cone Lateral & transverse wakes • Has both features: • Mach Cone • Lateral & transverse wakes

  21. Machconeexcitation V/CL = 1.17

  22. Mach cone + lateral wakes Nosenko et al. PRL 2002

  23. Microgravity • 3D physics

  24. 1996-1998 Sounding rockets Morfill et al., PRL 1999 • 2001 – 2002 • ISS - PKE Predecessor microgravity experiments

  25. Laser sheets for illuminating particles Cameras for imaging particles PKE vacuum chamber

  26. Flight hardware concept for optically-excited waves in 3D dusty plasmas imaging cameras diode laser (for imaging) cw Nd-YAG laser (manipulation) galvanometer scanning mirror shown in a mid-deck locker: plasma chamber & optics not shown: gas/vacuum, power, data

  27. dusty.physics.uiowa.edu

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