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PRODID:UW-Madison-Physics-Events
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UID:UW-Physics-Event-2605
DTSTART:20120213T180500Z
DURATION:PT1H0M0S
DTSTAMP:20260413T014646Z
LAST-MODIFIED:20120207T231251Z
LOCATION:2241 Chamberlin
SUMMARY:Complex Plasma - A Potential Field for Interdisciplinary Resea
 rch Using Laboratory and Space Experiments\, Plasma Physics (Physics/E
 CE/NE 922) Seminar\, Dr. Uwe Kokopka\, Max Planck Institute for Extrat
 errestrial Physics\, Garching
DESCRIPTION:Dust particles\, embedded in a plasma\, are getting charge
 d due to a variety of mechanisms like electron-/ion- bombardment or se
 condary electron emission. At low densities the dust in the plasma can
  be treated as an impurity that mainly probes the background plasma wi
 thout significantly altering it. At higher densities a change from dus
 t in plasma to a "dusty plasma" takes place. The dust species begin to
  alter the overall behavior of the other plasma components\, and vice 
 versa\, so that the dust has to be treated as an integral component. B
 oth situations can be frequently observed in astrophysical and plasma 
 processing environments. At sufficient high dust densities\, the dynam
 ics of the whole system eventually become dominated by the dust specie
 s\, since most of the inertia in the system is bound to it. In this si
 tuation the charged dust particles are often treated similarly to a on
 e-component system of directly interacting charged particles that are 
 "somehow" screened by the background plasma. Due to the high particle 
 mass\, the time and spatial scales of the dynamics are shifted towards
  macroscopic scales. Typically\, very fast plasma dynamics such as wav
 es\, diffusion\, or gyro motion of particles can then be observed simp
 ly with the naked eye. This so-called "complex plasma"\, named in anal
 ogy to complex fluids (e.g. colloidal particles in a liquid suspension
 )\, also shows strongly coupled phenomena like crystallization that ar
 e least expected to be present in a plasma environment. All of this is
  visible on the fundamental\, "atomic" scale of single (dust) particle
 s for the systems that can consist of just a few or up-to billions of 
 particles. This makes complex plasmas a very attractive research field
  which heavily supports and strongly benefits from interdisciplinary r
 esearch efforts. The high mass of the dust particles that shifts the d
 ynamics towards macroscopic scales has a drawback however. In a typica
 l laboratory complex plasma setup the dust sediments\, forming compres
 sed layers close to the lower sheath boundaries where the weight of th
 e particles is compensated by the effect of the sheath/pre-sheath elec
 tric field. Only small/light particles (~ 1 um) can easily fill the bu
 lk of the plasma. Alternatively\, experiments in u-gravity must be per
 formed. Since the discovery in 1994 of the crystalline state of a comp
 lex plasma\, the "plasma crystal"\, by my colleague H. Thomas\, I have
  studied a variety of topics related to complex plasmas. I have looked
  at fundamental themes like single particle interaction\, instabilitie
 s and the role of a magnetic fields in a complex plasmas. Additionally
 \, I studied interdisciplinary topics such as crystallization and flow
  dynamics. Some experiments were aimed at applications for dust remova
 l\, or dust growth\, that have relevance to plasma processing and fusi
 on. Experiments on dust coagulation and runaway growth provided uninte
 nded yet significant results regarding the astrophysical question of p
 lanet formation. The presentation contains an introduction to fundamen
 tal complex plasma research. I will discuss the charging and "somehow"
  screening of microparticles in a plasma environment as well as the ro
 le of gravity. Examples of laboratory and u-gravity experiments will b
 e shown\, demonstrating the interdisciplinary potential of complex pla
 smas research. Also two experimental setups that I have designed and b
 uilt to perform the shown experiments will be introduced: a unique hig
 h magnetic field plasma facility and a flexible plasma device\, the "P
 lasmaLab"\, that is foreseen to be operated as part of a future experi
 ment aboard the international space station (ISS). 
URL:https://www.physics.wisc.edu/events/?id=2605
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