dusty plasmas in the laboratory and space
DESCRIPTION
April 2003 APS Meeting Philadelphia, PA. Dusty Plasmas in the Laboratory and Space. Bob Merlino. Outline. Introduction – what is a dusty plasma and where are they found the charging of dust in a plasma devices for producing dusty plasmas waves in dusty plasmas. plasma = electrons + ions. - PowerPoint PPT PresentationTRANSCRIPT
Dusty Plasmas in the Laboratory and Space
Bob Merlino
April 2003 APS Meeting Philadelphia, PA
Outline
1) Introduction – what is a dusty plasma and where are they found
2) the charging of dust in a plasma
3) devices for producing dusty plasmas
4) waves in dusty plasmas
plasma = electrons + ions Plasma
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What is a dusty plasma?
D
• Debye shielding
small particle of solid matter
• becomes negatively charged
• absorbs electrons and ions
Dusty Plasma in the Universe
Dust represents much of the solid matter in the universe and this component often coexists with the ionized matter forming a dusty plasma.
Importance of Charged Dust
the dust acquires an electrical charge and thus is subject to electromagnetic as well as gravitational forces
the charged dust particles participate in the collective plasma processes
DUSTY PLASMAS
• Solar nebula• planetary rings• interstellar medium• comet tails• noctilucent clouds• lightning
• Microelectronic processing
• rocket exhaust• fusion devices
Natural Man-made
Our solar system accumulated out
of a dense cloud of gas and dust, forming everything that is now part of our world.
Rosette Nebula
Noctilucent Clouds (NLC)
• Occur in the summer polar mesosphere (~ 82 km)• 50 nm ice crystals• Associated with unusual radar echoes and reductions in the local ionospheric density
An early temperature measurement in a dusty plasma.
A flame is a very weakly ionized plasma that contains soot particles.
Comet Hale-Bopp
Spokes in Saturn’s B Ring
Voyager 2Nov. 1980
Cassini-HuygensJuly 2004
Semiconductor Processing System
PUMP
gas
13.56 MHz
substrate
EqE
mg
dust
silane (SiH4) + Ar + O2 SiO2 particles
Semiconductor Manufacturing
dustSi
Physics TodayAugust 1994
Dust Charging Processes
• electron and ion collection• secondary emission• UV induced photoelectron emission
Total current to a grain = 0
I = Ie + Ii + Isec + Ipe = 0
electronrepulsion
ion enhancement
The Charge on a Dust Grain
In typical lab plasmas Isec = Ipe = 0
Electron thermal speed >> ion thermal speed so the grainscharge to a negative potential VS relative to the plasma, untilthe condition Ie = Ii is achieved.
a
2
2
1
exp
akT
eV
m
kTenI
akT
eV
m
kTenI
i
S
i
iii
e
S
e
eee
Q = (4oa) VS
Typical Lab Plasma
For T e = Ti = T in a hydrogen plasma
VS = 2.5 (kT/e)
If T 1 eV and a = 1 m,
Q 2000 e
Mass m 5 1012 mp
Dust Charge Measurements
0
0.5
1
1.5
2
0 20 40 60 80 100 120
Diameter (micron)2
0
0.5
1
1.5
0 20 40 60 80 100 120 140 160
Electron Energy (eV)
Glass
Graphite
Walch, Horanyi, & Robertson,Phys. Rev. Lett. 75, 838 (1995)
Devices for producing dusty plasmas
RF Dusty Plasma Devices
PUMP
ANODE DISK
FIREROD
ROTATING DUST DISPENSER
PLASMA COLUMN
HOT PLATE
B
VIDEO CAMERA
CONFINED DUST GRAINS
GAS IN
GAS IN
Equipotential profiles of an anode double layer
anode
Device for studyingthe trapping of dust
in a dc glow discharge
DUST IN A GLOW DISCHARGE
N2
Vacuumvessel
PS
+
BAnode
Dust Tray
Anode Glow Plasma
Dust: kaolin (aluminum silicate)
E
mg
QE
wavefronts
Dust Acoustic Wave Image
dust mass
DA Dispersion relation
Monochromatic plane wave solutions for Te = Ti = T
1
1d
dDA Z
m
kTCf
where = ndo/n+o
0
4
8
12
16
0 50 100 150 200 (s-1)
Dust Acoustic WaveDispersion Relation
theory
Shocks in Dusty Plasma
Shocks in Dusty Plasma- results
Shocks in dusty plasmas Conclusions
• Ion acoustic compress-ional pulses are observed to steepen as they travel through a dusty plasma
• Relevant to astrophysical contexts where density disturbances travel through dust clouds
Conclusions and Outlook• Only recently have we begun to explore the
behavior of dusty plasmas in the laboratory-charging mechanisms, waves
• Technological applications of dusty plasmas are now being exploited
-ceramic deposition – composites
-growth of nanosize particles -diamond growth and deposition on metals
• Dusty plasmas in space are usually embedded in magnetic fields. This aspect of dusty plasmas has yet to be studied in the lab
R = Mv/QB >> typical lab plasmas
• Dusty plasmas may form strongly coupled systems known as Coulomb CrystalsCoulomb Crystals – a new area for plasma physics research
Dusty Plasma
DUST
RF Dusty Plasma Device