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Published byPrimrose Burns Modified over 8 years ago
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Optically-Excited Waves in 3D Dusty Plasmas John Goree The University of Iowa
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plasma = electrons + ions What is a dusty plasma? Debye shielding small particle of solid matter becomes negatively charged absorbs electrons and ions
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Solar system Rings of Saturn Comet tails Fundamental science Coulomb crystals Waves Manufacturing Particle contamination (Si wafer processing) Nanomaterial synthesis Who cares about dusty plasmas?
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Forces Acting on a Particle Coulomb QE Other forces: Gas drag Ion drag Thermophoresis Radiation Pressure Gravity mg
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Electrostatic trapping of particles Equipotential contours electrode positive potential electrode With gravity, particles sediment to high-field region 2-D layer Without gravity, particles fill 3-D volume QE mg
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polymer microspheres 8 m diameter Particles separation a 0.5 mm charge Q - 10 4 e
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Same: Coulomb repulsion Crystals Different: Dusty plasma has much lower damping rate wave propagation is easier Comparison to Colloidal Suspensions
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2D physics: Ground-based 3D physics: Flight Experiments described in this talk
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triangular lattice with hexagonal symmetry 2D lattice Yukawa inter-particle potential
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Two modes in a lattice
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Dispersion relations in 2D triangular lattice Wang et al. PRL 2001 =0,
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Setup
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scanning mirror Scanning mirror Ar laser beam
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Longitudinal wave 4mm k Laser incident here f = 1.8 Hz
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Random particle motion No Laser! = compression + shear 4mm Nunomura et al. PRL 2002
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Phonon spectrum & sinusoidally-excited waves Nunomura et al. PRL 2002
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Mach cones
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Mach cone angle C = U Sin U
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Lateral wake Transverse Wake Ship’s wake
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water air Wake pattern is determined by dispersion relation Mach cone Lateral & transverse wakes Has both features: Mach Cone Lateral & transverse wakes plasma crystal
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Mach cone excitation V/C L = 1.17
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Mach cone + lateral wakes Nosenko et al. PRL 2002
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3D physics Microgravity
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Predecessor microgravity experiments 1996-1998 Sounding rockets Morfill et al., PRL 1999 2001 – 2002 ISS - PKE
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PKE vacuum chamber Cameras for imaging particles Laser sheets for illuminating particles
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imaging cameras cw Nd-YAG laser (manipulation) galvanometer scanning mirror diode laser (for imaging) shown in a mid-deck locker:plasma chamber & optics not shown: gas/vacuum, power, data Flight hardware concept for optically-excited waves in 3D dusty plasmas
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