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Complex Plasmas as a Model for the
Quark-Gluon-Plasma Liquid
Markus H. Thoma Max-Planck-Institute for
Extraterrestrial Physics

1. Strongly Coupled Plasmas
2. Complex Plasmas
3. Applications to the Quark-Gluon Plasma

Supported by DLR (BMBF)
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Strongly Coupled Plasmas
Plasma ionized gas, 99 of visible matter in
Universe Plasmas generated by high temperatures,
electric fields, or radiation

• Classifications
• Non-relativistic relativistic plasmas (pair
  plasmas, QGP)
• Classical quantum plasmas (white dwarfs, QGP)
• Ideal strongly coupled plasmas (complex
  plasmas, QGP)

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Coulomb coupling parameter
Q charge of plasma particles d inter particle
distance T plasma temperature Ideal plasmas G
ltlt 1 (most plasmas G lt 10-3) Strongly coupled
plasmas G gt O (1) Examples ion component in
white dwarfs, high-density plasmas at
GSI Non-perturbative description, e.g.,
molecular dynamics One-component plasma, pure
Coulomb interaction (repulsive) G gt 172 g
Coulomb crystal
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Debye screening g Yukawa systems Additional
parameter k d/lD
Liquid phase G gt O (1) Purely repulsive
interaction g no gas-liquid transition, only
supercritical fluid
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2. Complex Plasmas
Dusty or complex plasmas multi component
plasmas containing ions, electrons, neutral gas,
and microparticles, e.g., dust Example low
temperature neon plasma in a dc- or rf discharge
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• Injection of microparticles with diameter
• 1 10 mm
• High electron mobility g microparticles
• collect electrons on surface g large
• negative charge Q 103 105 e
• Inter particle distance about 200 mm
• g G gtgt 1 g plasma crystal (predicted 1986,
  discovered 1994 at MPE)
• Observation illumination by laser sheet and
  recorded by CCD camera

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• Melting of plasma crystal by
• pressure reduction
• less neutral gas friction
• gtemperature increase
• gdecrease of Coulomb
• coupling parameter G Q2/(dT)

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Quantitive analysis of equation of state and
determination of G pair correlation function

• Crystal long range order
• sharp peaks at the nearest
• neighbors, next to nearest
• neighbors and so on
• Liquid short range order (incompressibility)
• gonly one clear peak corresponding to inter
  particle distance plus one or
• two broad and small peaks
• Gas no order gno clear peaks

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Gravity has strong influence on microparticles
gmicrogravity experiments
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Applications of complex plasmas 1. Model system
for phase transitions, crystallization, dynamical
behavior of liquids and plasmas on the
microscopic level 2. Astrophysics comets,
interstellar plasmas, star and planet formation,
planetary rings, 3. Technology
plasma coating and etching, e.g. microchip
production, problem dust contamination

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3. Applications to the Quark-Gluon Plasma

• Estimate of interaction parameter
• C 4/3 (quarks), C 3 (gluons)
• T 200 MeV g aS 0.3 - 0.5
• d 0.5 fm
• Ultrarelativistic plasma magnetic interaction as
  important as electric
• G 1.5 6 g QGP Liquid?
• RHIC data (hydrodynamical description
• with small viscosity, fast thermalization)
• indicate QGP Liquid
• Attractive and repulsive interaction g
• gas-liquid transition at a temperature
• of a few hundred MeV

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Static structure function (Fourier transform of
pair correlation function) g experimental and
theoretical analysis of liquids
Hard Thermal Loop approximation (T gtgt Tc)

• interacting gas
• QCD lattice simulations g QGP liquid?

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• Strongly coupled plasmas g cross section
  enhancement
• Reason Coulomb radius, rC Q2/E, larger than
  Debye screening length
• lD 1/mD g modification of Coulomb scattering
  theory
• g enhancement of ion-microparticle interaction
  (ion drag force)
• QGP rC /lD 1 5 g parton cross section
  enhancement by factor 2 9
• small mean free path l (corresponding to small
  viscostity h l) and fast
• thermalization.
• Additional cross section enhancement by
  non-linear and non-perturbative
• effects
• Implication enhancement of collisional
• energy loss,
• suppression of radiative energy loss by
• LPM effect (formation time)
• g jet quenching

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Conclusions

• Strongly coupled plasmas are of increasing
  importance in
• fundamental research as well as technology
• QGP and complex plasmas are important examples
  of strongly
• coupled plasmas
• QGP is the most challenging strongly coupled
  plasma
• Complex plasmas can easily be studied and used
  as a model
• for the QGP (phase transitions, correlation
  functions, cross sections, )
• RHIC and ISS provide very important information
  on strongly coupled
• plasmas