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

flux across the separatrix due to classical ion B×B drifts:
strong influx at the top of the plasma, and outflux above the
X-point. The comparison of the experimental and simulation
data was facilitated via common, MDSplus-based databases
generated under the auspices of the ITPA Divertor and SOL
working group.
9.2 EURATOM Associations
The participation of scientists from EURATOM Associations
continued to stay at a high level as in previous years.
In response to the call for participation in the 2008 AUG
campaign more than 160 experimental proposals have been
submitted by 75 scientists. More than 50 % of them are
non-IPP scientists. Besides several proposals from DIII-D,
the majority of external proposals originate from scientists
of 14 different EU Associations. In total the execution of
more than 1400 discharges has been requested. The international
AUG Programme Committee met in December and
approved a prioritized programme of roughly 800 shots.
Besides IPP ten Associations are represented in this body.
Andrew Kirk a scientist from MAST will take over the
management of the AUG Task Force III “SOL & Divertor
physics and first wall materials”. In the following the most
important contributions from Associations made in 2007
are summarized.
DCU – University College Cork:
Progress made during 2007 in the context of the ongoing
collaboration between IPP and University College Cork is
summarized as follows: A significant effort was expended
on CLISTE reconstructions as part of the recalibration of
the MSE diagnostic in light of systematic corrections to
radial channel locations discovered in early 2007. These
involved analysis of discharges with maximal diagnostic
information on rational surface locations to validate q profiles
obtained with MSE.
CLISTE has been extended to improve the modelling of disrupting
plasmas and now can generate interpretive equilibria
(including halo currents) for plasmas as small as 20 cm in
radius resting on divertor structures. The predictive Garching
Equilibrium Code can now generate ITER equilibria in AUG
shotfile format and construction of a database is underway.
The study of TAE character and stability has been completed
from discharges performed during the 2006 experimental
campaign for cases with ICRH only and combined ICRH
and NBI. Using MSE data, the quality of current profile
reconstructions using TAE mode positions from ICRH-only
discharges and ICRH with beatwaves has been confirmed.
These results will be used to describe in detail the nature and
uses of TAE in ASDEX Upgrade. TAE were also observed
in discharges from the first period of the 2007 campaign, the
first using a full tungsten machine. TAE activity from these
discharges differs significantly from the previous campaign
and analysis of the data is in progress.
ASDEX Upgrade
22
ENEA – Consorzio RFX, Padova:
The ORBIT code has been used to study the fast ion
dynamics in AUG and thus to contribute to the analysis of
the fast ion loss diagnostic measurements (FILD). Several
improvements and corrections have been implemented in
the code in order to perform more realistic simulations to
be compared with experimental data. In particular, the use
of equilibria in straight field lines has been assessed; this has
allowed fast ion physics to be studied in the real D-shaped
geometry of the device instead of a circular approximation
with Boozer co-ordinates. The equilibrium quantities are
computed by the VMEC code and adapted to be accessible
by ORBIT. The main application of the code has been a
study of the fast ion losses induced by Neoclassical Tearing
Modes. The influence of the toroidal magnetic field ripple
has been studied as well. As a further improvement electric
field effects have been implemented to deal with rotating
NTMs. An algorithm to obtain stationary conditions has
been introduced by replacing the lost deuterons with new
ones belonging to the same space and velocity distribution,
which characterizes the ions injected by the NBI system.
Simulations with rotating modes have confirmed most of
the results performed with a stationary mode. It has been
observed that at higher mode rotation frequencies larger
losses occur. This partly agrees with the experimental data,
but further analysis is still needed. In addition, investigations
of the internal structure of TAE modes are reported in
section 6.4.
HAS – KFKI Budapest:
The triggering mechanism of type-III ELMs was investigated
in detail by linking the dynamics of pellet-triggered
ELMs to the pellet trajectory. In order to study the pelletinduced
perturbation which triggers the ELM, magnetic
pick-up coil signals were analysed in ohmic discharges.
Methane doped deuterium pellet experiments were carried
out to study the effect of doping on penetration and pellet
cloud properties. Pellets with methane content between 0.44
and 2.4 % were used.
The effect of pellet injection on target plasma radiation was
investigated by the multi-chord SXR and bolometer systems.
An increase of the total radiation during pellet injection was
observed showing radiation coming from the HFS where the
pellet is ablated. SXR investigations revealed a poloidally
symmetric decrease of the plasma emissivity propagating
inwards during pellet ablation (see section 6.7). Temperature
measurements indicate that the emissivity drop is caused by
the cooling of the plasma.
Further testing was done with a new Lithium ion source
with a surface twice that of the usual one. Although up to
6 mA ion current could be reached the long term reliability
of the source is still not sufficient. The possibility of density
fluctuation measurement using the AUG lithium beam diagnostic
was studied with a single channel observation system.