Transcript Dusty Plasmas in the Laboratory and Space

April 2003 APS Meeting Philadelphia, PA
Dusty Plasmas in the
Laboratory and Space
Bob Merlino
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
What is a dusty
plasma?
-
plasma = electrons + ions
Plasma
-
small particle
of solid matter
• absorbs
electrons and
ions
+
+
+
-
+
+
-
• becomes
negatively
charged
+
+
D
-
• Debye
shielding
-
+
+
-
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
Natural
•
•
•
•
•
•
Solar nebula
planetary rings
interstellar medium
comet tails
noctilucent clouds
lightning
Man-made
• Microelectronic
processing
• rocket exhaust
• fusion devices
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
A flame is a very weakly ionized plasma
that contains soot particles.
An early temperature measurement in a dusty plasma.
Comet Hale-Bopp
Spokes in Saturn’s B Ring
Voyager 2
Nov. 1980
CassiniHuygens
July 2004
Semiconductor Processing System
dust
silane (SiH4) + Ar + O2  SiO2 particles
Semiconductor Manufacturing
Si
dust
Physics Today
August 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
The Charge on a Dust Grain
In typical lab plasmas Isec = Ipe = 0
Electron thermal speed >> ion thermal speed so the grains
charge to a negative potential VS relative to the plasma, until
the condition Ie = Ii is achieved.
electron
repulsion


I e  ene
kTe
me
I i  eni
kTi
mi
eVS
 a 2
exp
 kTe 
 eVS 
1 
 a 2
kTi 

a
Q = (4eoa) VS
ion enhancement
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
2
1.5
Walch, Horanyi, & Robertson,
Phys. Rev. Lett. 75, 838 (1995)
1
0.5
0
0
20
40
60
80
100
120
Diameter (micron)
2
1.5
Graphite
1
Glass
0.5
0
0
20
40
60
80
100
Electron Energy (eV)
120
140
160
Devices for producing
dusty plasmas
RF Dusty Plasma Devices
Device for studying
the trapping of dust
in a dc glow
discharge
GAS IN
PLASMA COLUMN
FIREROD
ANODE
DISK
B
GAS IN
ROTATING DUST
DISPENSER
HOT PLATE
CONFINED
DUST GRAINS
PUMP
VIDEO
CAMERA
Equipotential profiles
of an anode double
layer
anode
DUST IN A GLOW DISCHARGE
B
QE
Anode
Anode Glow
Plasma
N2
E
Dust Tray
+
mg
PS
Vacuum
vessel
Dust: kaolin (aluminum silicate)
Dust Acoustic Wave Image
wavefronts
DA Dispersion relation
Monochromatic plane wave solutions
for Te = Ti = T
kT
1 
f  CDA 
Zd
md
1 
where  = ndo/n+o
dust mass
Dust Acoustic Wave
Dispersion Relation
theory
Shocks in Dusty Plasma
Shocks in Dusty Plasma- results
Shocks in dusty plasmas
Conclusions
• Ion acoustic compressional 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 Crystals – a new
area for plasma physics research
Dusty Plasma
DUST
RF Dusty Plasma Device