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Radiation pressure and gas drag forces on a single particle and wave excitation in a dusty plasma

Radiation pressure and gas drag forces on a single particle and wave excitation in a dusty plasma. B. Liu, J. Goree, V. Nosenko, K. Avinash. plasma = electrons + ions. small particle of solid matter. absorbs electrons and ions. becomes negatively charged. Debye shielding.

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Radiation pressure and gas drag forces on a single particle and wave excitation in a dusty plasma

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  1. Radiation pressure and gas drag forces on a single particle and wave excitation in a dusty plasma B. Liu, J. Goree, V. Nosenko, K. Avinash

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

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

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

  5. Confinement of 2D monolayer • Interparticle interaction is repulsive Coulomb (Yukawa) • External confinement by curved electric sheath above lower electrode

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

  7. momentum imparted to microsphere Radiation Pressure Force incident laser intensity I transparent microsphere Force =0.97I rp2

  8. Setup Argon laser pushes particles in the monolayer

  9. Chopping chopped beam beam dump scanning mirror chops the beam Ar laser mirror

  10. laser beam • Accelerated by laser radiation pressure • Restored by confining potential Coulomb radiation pressure drag • Damped by gas drag Single-particle laser acceleration

  11. 2 mm Ar laser sheet Movie of particle accelerated by laser beam

  12. Equation of motion • Assumption: • The dominant forces are • Gravity • Vertical sheath electric field • Radiation pressure force • Drag force • Horizontal confining potential • One dimensional motion

  13. record particle’s orbit R R Gas drag coefficient R is an adjustable parameter to minimize the discrepancy between and . Calculation: radiation pressure, gas drag, confining potential

  14. Horizontal confining potential energy

  15. Radiationpressureforce

  16. Gas drag force

  17. Coefficients for radiation pressure and gas drag Radiation pressure q result: measurment0.94  0.11 ray optic theory0.97 Gas drag result: measurment1.26  0.13 Epstein theory 1 ~ 1.44 Epstein, Phys. Rev. 1924

  18. Laser sheet Application of radiation pressure force

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

  20. laser beam y x z Waves in one-dimensional dusty plasma chain • Longitudinal (along the chain) : acoustic • Transverse (perpendicular to the chain) : optical • The oscillation in • y direction ( horizontal confining potential) • z direction ( potential well formed by gravity and sheath )

  21. optical acoustic Optical mode in solid(two atom in primitive cell)

  22. Optical mode in one-dimensional chain • Assumptions: • One dimension, infinite in x direction • Parabolic confinement in y direction • Yukuwa interaction potential • Nearest neighbor interaction • No gas damping Optical: Acoustic:

  23. “Optical” branch Acoustic branch Dispersionrelation

  24. 22-particle chain Ashtray electrode z y x Formation of one-dimensional chain

  25. y x Bifurcation of chain • Potential gradient in x direction • Minimum potential energy requirement • Particle-particle interaction energy • Confining potential energy

  26. 1 2 Case 1 No bifurcation condition Case 2 Ux Uy x y Bifurcation condition

  27. Resonance frequency:x x = 0.07 Hz Single-particle laser acceleration

  28. Resonance frequency:y laser-excited resonance vibration laser sheet

  29. Resonance frequency:y Velocity autocorrelation function of random motion

  30. Excitation of optical mode Laser beam

  31. Excitation of optical mode Laser beam

  32. dusty.physics.uiowa.edu

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