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

diameter (instead of originally 73 mm) and a surface curvature
radius of 350 mm (instead of 1100 mm) are loaded with
the same stresses and strains as the full sized ones by applying
only 10 % of the compression force. The scaling is based
on extensive FE calculations. With the BAM equipment,
experiments can be performed much cheaper and quicker as
with the full size samples which were necessary during the
development phase. An additional advantage of the BAM
test bed is its suitability for experiments in liquid helium.
However, for achieving completely realistic environment
conditions, the equipment needs to be upgraded for vacuum
operation at 5 K and 80 K. The tests performed so far did
not completely confirm the previous full scale tests at KRP
which were done in vacuum at 80 K. Surprisingly, no stick
slip occurred during tests in LN 2 up to 15000 load cycles,
but stick slip was immediately present at the experiments in
LHe and ceased after about 50 cycles. This behaviour was
the same for MoS 2 -sprayed and -burnished counter-sides. In
order to clarify this issue tests in vacuum at these temperatures
would be necessary, however, the complete test program
is not yet finally decided. Systematic pad and counterside
MoS 2 layer ageing experiments were started in order to
estimate possible impact of the long exposure to air during
W7-X assembly. In order to reduce such ageing risks, in the
assembly as well as the torus hall the air humidity is kept
below 50 %. NSE pad and counter-side layer application
was supervised, and non-conformities were evaluated as
well as corresponding decisions prepared. In this context a
specification for tolerable defect sizes of sliding surfaces
was created.
4.2.2 Coil quench experiment
Detailed preparation of the intended experiment to mechanically
excite a non-planar coil by hitting it in cryogenic environment
under self-field magnetic load was started after
general consent for such an experiment was achieved within
IPP, with CEA Saclay, and with the coil manufacturer BNG.
The basic experimental procedure was decided, and preparatory
experiments were started. The real mechanical quench
experiment in Saclay is planned for autumn 2008 within an
available time window of the coil test schedule.
4.2.3 Materials
The material data base was maintained and continuously
supplemented as an ongoing activity. Cryogenic tensile tests
of welds and weld influence zones of cold- and warm-hardened
aluminium alloy conductor jacket material were done.
Orthotropic mechanical characteristics (stress-strain as well
as thermal contraction) of fibre-glass epoxy samples of the
bus-bar weld joint insulation were determined at liquid
helium temperature. Microstructure investigations and cryogenic
tensile tests were performed on a new Al-bronze alloy
for NSE/PSE/CE pad material, and further low temperature
Wendelstein 7-X
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pulling tests on high-quality steel (1.4429 ESU) for highly
loaded NSE pad frames. All these cryogenic tests were carried
out at the FZK. Collection and classification of coil
housing cast defects was almost completed.
4.3 Instrumentation
New strain gauge sensors with reduced temperature dependence
in cryogenic environment were introduced together
with copper plated steel compensation blocks for mechanical
structure instrumentation. This system was tested on
the non-planar coil AAB12 in Saclay and showed good
agreement with predictions from FE-calculations. Instrumentation
of the CSS with these sensors has started. The
extreme mechanical loads on the complex, non-linear magnet
structure necessitate its monitoring during operation. This
information about the mechanical behaviour has also to be
gathered for adaptation of the finite element models to the
as-built material and geometry characteristics in order to
define operational limits of the machine and evaluate possible
abnormal behaviour. An adequate structure instrumentation
concept, based on mechanical analysis results, was
defined. The complete mechanical measurement system
relies upon strain gauges which, besides measuring stress
and strain, will also be used in combination with specially
developed equipment to indicate component deformations
and relative movements. Collision monitoring in critical
areas of ports and the coil header regions will be done
with single contact foils. A strain gauge system including
the corresponding data acquisition equipment was adapted
for dynamic measurements which is required for the
mechanical quench experiment. Much work was also spent
on collection, analysis, and interpretation of strain measurement
results of the CEA Saclay coil tests. This study finally
confirmed the functionality of the pre-existing strain gauges
on the non-planar coils. The suitability of the already assembled
PLC strain gauges, or necessity to exchange them, is
still under discussion, corresponding investigations are
ongoing.
5 Design and Configuration
The subdivision ”Design and Configuration” was established
in summer 2007 to adapt the organisation of the W7-X
project to the increasing assembly activities. In order to support
these activities it was considered necessary to establish
the department ”Configuration Management”. The purpose
of this department was to speedily implement component
changes caused by design changes and to properly keep
track of fabrication errors. In the past some of these tasks
where taken care of within the department System Coordination.
The number of components within the cryostat, the
complexity of their arrangement and the multitude of relative
movements possible in the various operational modes