optically-excited waves in 3d dusty plasmas
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
The University of IowaThe University of Iowa
Optically-Excited Waves in 3D Dusty Plasmas
John Goree The University of Iowa
The University of IowaThe University of Iowa
plasma = electrons + ions Plasma
+
-
+
+
+
+
+
+
+
- -
-
-
--
-
+
-
What is a dusty plasma?
D
• Debye shielding
small particle of solid matter
• becomes negatively charged
• absorbs electrons and ions
The University of IowaThe University of Iowa
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?
The University of IowaThe University of Iowa
Forces Acting on a Particle
Coulomb
QE
Other forces:• Gas drag
• Ion drag• Thermophoresis• Radiation Pressure
Gravity
mg
The University of IowaThe University of Iowa
Electrostatic trapping of particles
Equipotentialcontours
electrode
electrode
positive
potential
electrode
electrode
With gravity, particles sediment to high-field region 2-D layer
Without gravity, particles fill 3-D volume
QE
mg
The University of IowaThe University of Iowa
polymer microspheres
8 m diameter
Particles
separation a 0.5 mm
charge Q - 104 e
The University of IowaThe University of Iowa
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-particlepotential
The University of IowaThe University of Iowa
Two modesin a lattice
The University of IowaThe University of Iowa
0 0.5 1 1.5 20
1
2
3
4
ka
/
0
Transverse mode
Longitudinal mode
=1.2, /0=0.39Dispersion relationsin 2D triangular lattice
Wang et al. PRL 2001
=0,
k
The University of IowaThe University of Iowa
Setup
The University of IowaThe University of Iowa
scanningmirror
Scanningmirror
Ar laser beam
The University of IowaThe University of Iowa
Longitudinal wave
4mm
k Laser incident here
f = 1.8 Hz
The University of IowaThe University of Iowa
Random particle motion
No Laser!
= compression + shear
4mm
Nunomura et al. PRL 2002
The University of IowaThe University of Iowa
Phonon spectrum
-6.0 -4.0 -2.0 0.0 2.0 4.0 6.0
6.0
4.0
2.0
0.0
Longitudinal mode6.0
4.0
2.0
0.0
k (mm-1)
f (H
z)f (
Hz)
ka/-2.0 -1.5 -1.0 0.5 0.0 0.5 1.0 1.5 2.0
/
0
3.0
2.0
1.0
0.0
4.0
/
0
3.0
2.0
1.0
0.0
4.0
5
10
15
En
erg y
den
s ity
/ k B
T (
10-
3m
m2s)
k
a
= 0°
Transverse mode
& sinusoidally-excited waves
Nunomura et al. PRL 2002
The University of IowaThe University of Iowa
Machcones
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Machconeangle
C = U Sin
U
k
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Lateral wakeTransverse Wake
Ship’swake
k
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water
air
Wake pattern is determined bydispersion relation
Mach cone
Lateral & transverse wakes
k
k
Has both features:• Mach Cone• Lateral & transverse wakes
plasma crystal
0 0.5 1 1.5 20
1
2
3
4
ka
/
0
Transverse mode
Longitudinal mode
=1.2, /0=0.39
The University of IowaThe University of Iowa
Machconeexcitation
V/CL = 1.17
The University of IowaThe University of Iowa
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
The University of IowaThe University of Iowa
PKE vacuum chamber
insulator
ground
plasm a&
particles
ground
ground
rf electrode
fieldof
view
dust dispenser
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
The University of IowaThe University of Iowa