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Dusty Plasmas in the Laboratory and Space

VIEWS: 5 PAGES: 32

									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
                                                     D
    charged                                                                          -
                                                    -                +
  • 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               Man-made

•   Solar nebula          • Microelectronic
•   planetary rings         processing
•   interstellar medium   • rocket exhaust
•   comet tails           • fusion devices
•   noctilucent clouds
•   lightning
                 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




                     Cassini-
                     Huygens
                     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
                        eVS           repulsion
            kTe
I e  ene          exp kT   a 2
                                                       a
            me          e
            kTi    eVS 
I i  eni         1 
                            a 2            Q = (4eoa) VS
            mi         kTi 
                            
                                    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,
                                   1
Phys. Rev. Lett. 75, 838 (1995)
                                  0.5


                                   0
                                        0    20        40        60    80     100       120
                                                       Diameter (micron)
                                    2


                                  1.5
                                                                            Graphite

                                    1


                                  0.5                        Glass


                                    0
                                        0   20    40        60   80   100   120   140    160
                                                   Electron Energy (eV)
Devices for producing
   dusty plasmas
RF Dusty Plasma Devices
Device for studying                                        GAS IN


the trapping of dust   PLASMA COLUMN        FIREROD
                                                           ANODE
    in a dc glow                                            DISK


      discharge             B

                                GAS IN
                                      ROTATING DUST
                                        DISPENSER
                                                                     VIDEO
                   HOT PLATE                                PUMP    CAMERA
                                              CONFINED
                                             DUST GRAINS




                                         Equipotential profiles
                                         of an anode double
                                         layer
                                   anode
          DUST IN A GLOW DISCHARGE


QE                        B                    N2
                                       Anode
        Anode Glow
          Plasma
                              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 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 Crystals – a new
  area for plasma physics research
Dusty Plasma




               DUST
RF Dusty Plasma Device

								
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