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Dusty plasmas in basic science, astronomy, industry & fusion. John Goree The Univ. of Iowa. The growth of dusty plasmas as a field of research. Outline. What is dust? Formation of dust Fusion Industry Astronomy Dust charge Forces acting on dust Some physics experiments:

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    1. Dusty plasmas in basic science, astronomy, industry & fusion John Goree The Univ. of Iowa

    2. The growth of dusty plasmas as a field of research

    3. Outline • What is dust? • Formation of dust • Fusion • Industry • Astronomy • Dust charge • Forces acting on dust • Some physics experiments: • Voids under microgravity conditions • Strongly-coupled vs. Weakly-coupled Plasmas • Waves & Instabilities • Shear flow • Wakes

    4. What is dust? Astronomy: “dust” Semiconductor industry “particulates” or “particles” M16 pillar Credit: NASA, HST, J. Hester & P. Scowen (ASU) G.S. Selwyn, Plasma Sources Sci. Tehcnol. 3, 340 (1994) “Dust” = small particles of solid matter, 10 nm – 1 mm, usually dielectric

    5. What is dust? Safety Issues for fusion Radiological • Dust: • activated • retains tritium • ITER safety limit: 350 kg Tungsten dust Fire & chemical explosion • Hydrogen: • stored in dust • released during accidental exposure to: • air • steam • ITER safety limit: 6 kg dust allowed on hot surfaces Phil Sharpe Fusion Safety Program, Idaho National Laboratory Dust in Fusion Plasmas Workshop 2005

    6. Formation of dust • What is dust? • Formation of dust • Fusion • Industry • Astronomy • Dust charge • Forces acting on dust • Some physics experiments: • Voids under microgravity conditions • Strongly-coupled vs. Weakly-coupled Plasmas • Waves & Instabilities • Shear flow • Wakes

    7. Formation • What’s the source of dust in a plasma? • Produced on surfaces • Flaking of deposited films • Bubbles & blistering of surfaces • Produced in the gas phase • Nucleation • Coagulation • Purchased from vendor

    8. Formation: tokamaks Fusion: various shapes of dust collected from the Tore Supra tokamak • Composition is mainly: • carbon • constituents of stainless steel Phil Sharpe Fusion Safety Program, Idaho National Laboratory Dust in Fusion Plasmas Workshop 2005

    9. Formation: tokamaks 2 mm Tungsten dust formation: flaking from He bubbles Divertor Plasma Simulator NAGDIS-II Surface Temp.: 2200 K Flux: 8.3×1022 m-2s-1 Ion Energy: 15 eV Time: 104 s N. Ohno, S. Takamura, Dai. Nishijima “Formation and Transport of Dust in the Divertor Plasma Simulators” Dust in Fusion Plasmas Workshop 2005

    10. Formation: tokamaks Observation of High Z Dust in TRIAM-1M by Fast Framing Camera, 4500 fps Dust High Z dust is emitted from the Mo poloidal limiter. N. Ohno, S. Takamura, Dai. Nishijima “Formation and Transport of Dust in the Divertor Plasma Simulators” Dust in Fusion Plasmas Workshop 2005 Poloidal Limiter

    11. A lesson from the semiconductor industry Particles were always there, but you didn’t know it until you used the rightdiagnostics: camera imaging in-situ electron microscopy ex-situ G.S. Selwyn, Plasma Sources Sci. Tehcnol. 3, 340 (1994)

    12. Formation: gas phase • Gas-phase formation in astrophysics: • Vapor flowing outward from a carbon star cools & nucleates Þ dust • Dust grains then grow by “coagulation” M16 pillar, Credit: NASA, HST, J. Hester & P. Scowen (ASU)

    13. Formation: gas phase • Gas-phase formation G. Praburam and J. Goree Astrophys. J 1995

    14. Formation: gas phase • Cauliflower particles grow in the gas phase: intact fractured Gary Selwyn, IBM, 1989 Ganguly et al., J. Vac. Sci. Technol. 1993

    15. Formation: gas phase 300 nm Particles grown by sputtering tungsten Coagulated particles consisting of 3+ cauliflowers D. Samsonov and J. Goree J. Vac. Sci. Technol. A 1999

    16. Formation: gas phase Particles grown by sputtering graphite D. Samsonov and J. Goree J. Vac. Sci. Technol. A 1999

    17. Formation: gas phase Particles grown by sputtering aluminum D. Samsonov and J. Goree J. Vac. Sci. Technol. A 1999

    18. Formation: purchased from vendor • Polymer microspheres: • melamine-formaldehyde • diameter 8.09 ± 0.18 mm • used in basic science experiments • introduced into plasma with a “salt shaker”

    19. Outline • What is dust? • Formation of dust • Fusion • Industry • Astronomy • Dust charge • Forces acting on dust • Some physics experiments: • Voids under microgravity conditions • Strongly-coupled vs. Weakly-coupled Plasmas • Waves & Instabilities • Shear flow • Wakes

    20. Charging: mechanisms Ielectron collection + Iion collection + Ielectron emission Ielectron collection + Iion collection H+ H+ e- e- + _ e- • Electron emission • secondary emission due to e- impact • photoemission • thermionic • Þpositive charge Charging by collecting electrons and ions only Þnegative charge Goree, Plasma Sources Sci. Technol. 1994

    21. Charging: mechanisms H+ e- • Equilibrium: • Itotal = 0 at the “floating potential” V: • Q = CV • C = 4pe0a • is capacitance of sphere of radius a a e- surface potentialV Particles immersed in a plasma collect currents: Itotal = Ielectron collection + Iion collection + Ielectronemission Each of these currents depends on the potential V of the particle Goree, Plasma Sources Sci. Technol. 1994

    22. Charging: mechanisms Ielectron collection + Iion collection H+ e- _ • Charging by collecting electrons & ions only • Consider a particle that is suddenly exposed to plasma: • Initially it collects electrons more rapidly than ions, due to higher vte • Eventually it reaches equilibrium “floating potential”: • Hydrogen, Ti = Te • V = -2.5 kTe • Example: • Parameters: • Te= 1 eV • a = 1 mm • Charge: Q = - 1737 e Goree, Plasma Sources Sci. Technol. 1994

    23. Forces • What is dust? • Formation of dust • Fusion • Industry • Astronomy • Pure physics • Dust charge • Forces acting on dust • Some pure physics experiments: • Strongly-coupled vs. Weakly-coupled Plasmas • Waves & Instabilities • Shear flow • Wakes

    24. Forces Forces acting on a particle CoulombQEµa ¬ provides levitation Lorentz Q v´ B µa ¬ tiny except in astronomy Ion dragµ a2¬ big for high-density plasmas Radiation pressureµ a2¬ if a laser beam hits particle Gas dragµa2¬ requires gas Thermophoretic force µa2¬ requires gas Gravityµa3¬ tiny unless a > 0.1 mm

    25. Ion drag force Momentum is imparted to the dust particle _ _ Orbit force: Ion orbit is deflected Collection force: Ion strikes particle

    26. Ion drag force • Void is due to • ion drag • Dust (laser light scattering from a horizontal laser sheet) • Glow • Plasma: • RF parallel-plate • glow discharge • argon gas • Dust: • nm size • carbon • grown by sputtering graphite target D. Samsonov and J. Goree Instabilities in a Dusty Plasma with Ion Drag and Ionization Physical Review E Vol. 59, 1047-1058, 1999

    27. Ion drag force • Void is due to • ion drag • Dust (laser light scattering from a horizontal laser sheet) • Glow • Plasma: • RF parallel-plate • glow discharge • argon gas • Dust: • nm size • carbon • grown by sputtering graphite target D. Samsonov and J. Goree Instabilities in a Dusty Plasma with Ion Drag and Ionization Physical Review E Vol. 59, 1047-1058, 1999

    28. Ion drag force How ion drag produces a void: Ionization source Positive plasma potl Outward ion flow dust void J. Goree, G. E. Morfill, V. N. Tsytovich and S. V. Vladimirov, Theory of Dust Voids in Plasmas, Physical Review E Vol. 59, 7055-7067, 1999

    29. Ion drag force Collection force from OML model Orbit force from Rosenbluth potential • Ion drag force • Two contributions: • Orbit force (this is the usual drag force for Coulomb collisions, except that lnL is problematic) • Collection force (ions actually strike the particle) • Depends on ion velocity ui • Force µni µ V µ V2 µ V-2 Te / Ti = 60, mi = 40 amu, lD = 130 mm Ion drag is normalized by 4 p ni a2 Te / (Ti/Te)0.5 J. Goree, G. E. Morfill, V. N. Tsytovich and S. V. Vladimirov, Theory of Dust Voids in Plasmas, Physical Review E Vol. 59, 7055-7067, 1999 E. C. Whipple, Rep. Prog. Phys. 44, 1198 (1981)

    30. Ion drag force • Ion drag force • Fusion edge plasma parameters: • Te = Ti, deuterium mass Te / Ti = 1, mi = 2 amu, lD = 13 mm Ion drag is normalized by 4 p ni a2 Te / (Ti/Te)0.5 Data computed March 2005 using the same code as in J. Goree, G. E. Morfill, V. N. Tsytovich and S. V. Vladimirov, Theory of Dust Voids in Plasmas, Physical Review E Vol. 59, 7055-7067, 1999

    31. Gas drag force Stokes-flow regime • molecular-flow regime • Epstein: • Ngasgas atom: number density • mgasmass • cgasmean thermal speed • V velocity of particle with respect to the gas • d dimensionless, ranges from 1.0 to 1.442 • P. Epstein, Phys. Rev. 23, 710 (1924). • M. J. Baines, I. P. Williams, and A. S. Asebiomo, Mon. Not. R. Astron. Soc. 130, 63 (1965). Gas drag

    32. Radiation pressure force transparent microsphere incident laser momentum imparted to microsphere Radiation pressure B. Liu, V. Nosenko, J. Goree and L. Boufendi, Phys. Plasmas (2003).

    33. Physics experiments • What is dust? • Formation of dust • Fusion • Industry • Astronomy • Pure physics • Dust charge • Forces acting on dust • Some physics experiments: • Microgravity conditions • Strongly-coupled vs. Weakly-coupled Plasmas • Waves & Instabilities • Shear flow • Wakes

    34. Physics experiments Remainder of this talk: All experiments performed with polymer microspheres

    35. Microgravity conditions electrode Equipotential Contours (RF glow discharge) 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

    36. Microgravity conditions To obtain a 3D dust suspension, use zero g conditions: Parabolic flights, NASA KC-135

    37. Microgravity conditions Parabolic flights, NASA KC-135

    38. Microgravity conditions Parabolic flights, NASA KC-135 video

    39. Strongly-coupled vs. weakly-coupled plasmas “strongly coupled” dusty plasma: Q big star interior: r small pure-ion plasma: T small G > 1 plasma is like a solid or a liquid G << 1 plasma is like a gas Coulomb coupling parameter:

    40. Physics experiments Next: Waves in a weakly-coupled dusty plasma

    41. Dust acoustic wave experiment: Kiel Univ. camera plasma column probes dust tray RF-discharge anodicplasma Parameter: gas: Argon p = 1.0 .. 2.5 Pa ni = 1015 m-3 B = 20 .. 80 mT Anode: UA = 50 .. 100 V IA = 3 .. 12 mA dust: MF-spheres d = 1 µm nd = 0.5 .. 3 x 1011 m-3 particles anode 3 cm Courtesy Alexander Piel, Kiel University, Germany, 2005 41 Dusty Plasma Research, A. Piel, 2005

    42. Dust acoustic wave experiment: Kiel Univ. 15 mm Time lapse 1:10 p = 2.5 Pa IA = 10 mA B = 20 mT Courtesy Alexander Piel, Kiel University, Germany, 2005 42 Dusty Plasma Research, A. Piel, 2005

    43. Physics experiments Next: Shear flow in a strongly-coupled dusty plasma (plasma crystal).

    44. Shear flow in a 2D dusty plasma • two Ar+ laser beams: • 0.61 mm width • rastered into vertical sheets

    45. Shear flow in a strongly-coupled dusty plasma undisturbed monolayer Ar+ laser pushes particles Transport: radiation pressure medium power: plastic deformation, flow highpower: melting the lattice low power: slow deformation, rotation

    46. Zoom-in view Shear flow in a strongly-coupled dusty plasma A 2D liquid, observed at an atomistic level

    47. Video data: Shear flow in a strongly-coupled dusty plasma particle’s x,y position measured in each video frame Data recorded: x & v for each particle i.e., a kinetic approach Next step in analysis: convert to a continuum approach, by spatial averaging

    48. Velocity profiles Shear flow in a strongly-coupled dusty plasma

    49. Navier-Stokes equation v fluid velocity r areal mass density (2D) p pressure (2D) n = h / r kinematic viscosity (2D) z second viscosity (2D) nE gas drag

    50. Navier-Stokes equation • Our experiment: • 2D • ¶/¶t = 0 • ¶/¶x = 0 • vy = 0 Navier-Stokes equation reduces to: Þ nkinematic viscosity nEgas drag coefficient