Kein Folientitel

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Edge plasma physics a bridge between several
disciplines
Ralf Schneider and K. Matyash, N. McTaggart, M.
Warrier, X. Bonnin, A. Runov, M. Borchardt, J.
Riemann, A. Mutzke, H. Leyh, D. Coster, W.
Eckstein, R. Dohmen and many other colleagues
from USA, Europe and Japan
Ralf Schneider
IPP-Teilinstitut Greifswald, EURATOM Association,
Wendelsteinstraße 1, D-17491 Greifswald, Germany
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Strongly non-linear parallel heat conduction by
Coulomb collisions
Extreme anisotropy
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Can we manage the power load at the
plates? Development of computational tools to
model this power loading.
Estimate of power load
!
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Carbon deposition in divertor regions of JET and
ASDEX UPGRADE
Major topics tritium codeposition
chemical erosion
JET
Paul Coad (JET)
ASDEX UPGRADE
Achim von Keudell (IPP, Garching)
V. Rohde (IPP, Garching)
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Internal Structure of Graphite
Granule sizes microns Void sizes 0.1
microns Crystallite sizes 50-100
Ångstroms Micro-void sizes 5-10 Ångstroms
Multi-scale problem in space (1cm to Ångstroms)
and time (pico-seconds to seconds)
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• - Hydrogen in perfect crystal graphite 960
  atoms
• - Brenner potential, Nordlund range interaction
• - Berendsen thermostat, 150K to 900K for 100ps
• - Periodic boundary conditions

Developed by Kai Nordlund, Accelarator
laboratory, University of Helsinki
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150K
900K
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Two diffusion channels
No diffusion across graphene layers (150K 900K)
Lévy flights?
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Non-Arrhenius temperature dependence
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?0 Jump attempt frequency (s-1) Em Migration
Energy (eV) T Trapped species temperature (K)

• Assume
• Poisson process (assigns real time to the jumps)
• The jumps are not correlated

BKL algorithm (residence time algorithm A.B.
Bortz, M.H. Kalos, J.L. Lebowitz, J. Comp. Phys.
17 (1975) 10 Theoretical foundations of dynamical
Monte Carlo simulations, K.A. Fichthorn and W.H.
Weinberg, J. Chem. Phys. 95 (2) (1991) 1090-1096
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K.L. Wilson et al., Trapping, detrapping and
release of implanted hydrogen isotopes, Nucl.
Fusion 1 31-50 Suppl. S 1991
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TRIM, TRIDYN much faster than MD (simplified
physics)

• very good match of physical
• sputtering
• dynamical changes of surface
• composition

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Model system for chemical sputtering methane
plasma (2DX3DV PICMCC multispecies) Collaboration
with IEP5, Bochum University (Ivonne Möller)
ne 1010 cm-3, nH2 9.21014 cm-3, nCH4
71014 cm-3, p 0.085 Torr (11 Pa)
ne 109-1010 cm-3 nn 1015 -1016 cm-3 fRF
13.56 MHz
potential
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Negative charge due to higher electron mobility
Levitation in strong sheath electric field
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electric thrusters exhaust velocity larger than
in conventional chemical systems --gt much lower
mass of propellant
stationary plasma thruster(electron closed drift
or Morozov type)
exhaust
anode (neutral propellant)
cathode
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• - secondary electrons emitted from the wall
  (BN, Al2O3, SiO2) probabilistic model - all
  collisions included- ion-wall sputtering TRIDYN
• geometrical scaling constant Knudsen (?/L) and
  Larmor (rL/L) parameters

• Computational model parameters
• - Geometrical reducing factor
  f0.2
• Grid points 50x40
• Cell size
  ?x3?D
• Time step ?t?p-1/3
• Weight of macroparticle
  wp105, wN107
• Number of macroparticles N105
• Number of time step to reach staedy state
  Nt105
• Computational time 30 hh on 2.5
  Ghz

electron density
Francesco Taccogna, University of Bari
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Francesco Taccogna, University of Bari
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B2-Eirene, UEDGE, Finite volume codes for mixed
conduction convection problems
- Neutral physics (momentum losses, volume
recombination, operational scenarios, geometry
optimization) - Impurities (radiation, flows)
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Inclusion of drifts and currents flows, radial
electric field
Radial electric field Closed field lines
neoclassical Open field lines SOL physics
Radial electric field shear layer close to
separatrix (flow pattern)
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Divertor
Plasma
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r
Enhancement of radial transport due to
contribution from parallel transport
Electron temperature
Rechester Rosenbluth, Physical Review Letters,
1978
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Kolmogorov length LK is a measure of field line
ergodicity
Typical value in W7-X LK 10 30 m
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Problem numerical diffusion induced by
interpolation on the interface
Solutions
1) Optimized mesh (finite-difference scheme)
2) Monte-Carlo combined with Interpolated Cell
Mapping
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High accuracy transformation of the perpendicular
coordinates of a particle (mapping between cuts)
needed! (bicubic spline interpolation)
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1
Mesh optimization
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Field line tracing code
Magnetic field configuration data file
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5
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Metric coefficients code
Triangulation code
Mesh data file
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Transport code
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Neighborhood array data file
Metric coefficients data file
Temperature solution
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T (eV)
Normalized field line length
Ergodic effects lead to 3D modulation of long
open field lines
Cascading of energy from ergodic to open field
lines
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Feeding fluxes determined by field line length
No power load problem for W7-X
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Complex multi-scale physics requires complex
computational tools