IPP Annual Report 2007 - Max-Planck-Institut für Plasmaphysik ...

Tokamak Physics Division
Head: Prof. Dr. Sibylle Günter
Tokamak Edge Physics Group
Work in the group has balanced
the use of existing codes to understand
phenomena in the edge plasma
(or to identify discrepancies
between code and experiment),
and the improvement of the codes.
Current edge codes form an important
bridge between results
on present machines and divertor operation on ITER. The
present ITER divertor is based to a large extent on the results
of simulations with one of the existing edge codes, while a
number of edge codes are in use to understand present day
experimental results. To place the ITER predictions on a
firmer footing, an effort has been made to verify the existing
codes by careful code-code comparison, and then to validate
the codes against the experiment. This is done within the
framework of an ITPA DivSOL activity (DSOL-14), and
also as part of the activities of the EU Task Force on
Integrated Tokamak Modelling. In 2004, the results of the
EDGE2D-NIMBUS, B2-EIRENE (SOLPS5) comparison
for the D only case were reported together with some preliminary
results with drifts. During the 2007 JET edge modelling
campaign, these results were extended to D+C for
SOLPS, and some results for D and D+C for EDGE2D-
NIMBUS and EDGE2D-EIRENE were also obtained. One
of the major results was a renewed look at the atomic
physics being used in the edge codes. For one particular
case, the peak target electron temperature was found to
change by a factor of nearly 10 depending on the choice of
atomic physics (for hydrogen).
In-depth examination of earlier identified discrepancies
between SOLPS modelling and AUG experimental data was
continued. Three types of discrepancies – in the divertor
electron temperature T e , radial electric field E r and Mach
numbers of parallel ion flow in the main scrape-off layer
(SOL) M || – were linked together. A consistent picture of the
problems encountered by the code modelling has been confirmed.
The leading assumption about the origin of the discrepancies
is the neglect of kinetic effects in the parallel electron
heat transport from the SOL to divertor. Analysis of publications
related to the role of kinetic effects in the SOL reveals
a significant effect which they can have on the electron distribution
function near the target, resulting in higher parallel
electron heat flux and a large Debye sheath drop at the target.
Work has started on developing a kinetic treatment for the
edge plasma, with the intention of either coupling this to B2,
or to try to parameterize the results in some fashion for
inclusion in the fluid plasma code. In continuation of a project
on disruptions at JET, a series of modified pre-disruptive
Theoretical Plasma Physics
Head: Prof. Dr. Per Helander
The project “Theoretical Plasma Physics” is devoted
to first-principle based model developments
and combines the corresponding efforts of
the divisions Tokamak Physics and Stellarator
Theory, of the Junior Research Groups “Turbulence
in Magnetized Plasmas”, “Theory and Ab Initio
Simulation of Plasma Turbulence”, and “Computational
Material Science”, and the EURYI Research
Group “Zonal Flows”. It is headed by one theorist
on the board of scientific directors at a time.
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JET equilibria has been subjected
to thermal quench modelling
with the SOLPS package.
Development of version 6.0 of
the SOLPS package supporting
adaptive mesh refinement has
continued. Based on the current
implementation of the B2 fluid
code, approaches to implement a
generalized framework for the solution
of the fluid equations have
been studied. The main focus lies
on higher-order schemes for conservation laws on unstructured
quadrilateral meshes and efficient data structures enabling
later parallelization of core components of the code.
Other work included: (1) continuing activities associated
with the EFDA Task Force on Integrated Tokamak Modelling;
(2) maintenance, support, and further development of
the SOLPS code; (3) supporting the use of SOLPS at IPP to
(i) explore the differences between L- and H-mode edge profiles
in terms of the derived transport coefficients, (ii) explore
the impact of a killer gas puff on AUG, and (iii) explore the
process of detachment.
MHD Theory Group
Heat Transport in Magnetic Islands
Heat diffusion studies using a recently developed numerical
scheme were continued. For cylindrical geometry, heat diffusion
across magnetic islands and ergodic layers has been
studied in detail. The effect of the observed island temperature
flattening on the stability of Neoclassical Tearing Modes
was examined. It was found that the neoclassical island drive
is significantly stronger for realistic island parameters than
predicted by Fitzpatrick 1 .
A new code has been implemented which applies the numerical
scheme to toroidal geometries using straight field line
coordinates. First results for magnetic islands and ergodic
layers in realistic ASDEX Upgrade equilibria suggest that
cases with realistic heat diffusion anisotropies can be very
well resolved.
Fully Three-dimensional Resistive Wall Mode and Feedback
Stabilization Studies
The feedback stabilization of Resistive Wall Modes (RWMs)
has been studied in the presence of multiply connected wall
structures using the fully three dimensional CAS3D, STAR-
WALL, and OPTIM codes. The coupling of toroidal modes
in 3D has been taken into account. The codes have been
applied to an ITER and an ASDEX Upgrade like equilibrium
with β N =2.51 and β N =2.62, respectively. For both cases stable
solutions have been found.
1 R. Fitzpatrick, Physics of Plasmas 2, 825 (1995)