The ITER toroidal field model coil project

204 A. Ulbricht et al. / Fusion Engineering and Design 73 (2005) 189–327
bonded to the ground insulation of the coil so that the
insulation was electrically tight in case of a vacuum
breakdown and passing through the Paschen minimum
pressure.
3.7.2. Temperature sensors
Three types of temperature sensors were used to
monitor the temperature of the coolant of the coil,
the case and the ICS. Due to the high magnetic field
the cheaper TVO sensors could not be used in certain
positions. For measuring the helium temperature, 13
CERNOX sensors (11 for the winding and 2 for the
ICS) were placed directly in the helium flow inside
the cooling pipes at the inlet and outlet points of the
flow scheme. However, 31 TVO sensors were installed
for monitoring and controlling the cool down process.
They were positioned on the surface of the coil
case, the surface of the ICS and on cooling pipes.
Additional 4 Pt100 sensors were used to monitor the
hot spots of the coil case and the ICS during cool
down.
3.7.3. Strain gauges, rosettes and displacement
transducers
The Lorentz forces deformed the overall and crosssectional
shape of the coil case and the ICS. Thirtyfour
individual strain gauges and 11 rosettes were
installed to measure the surface strains at the main
symmetry planes of TFMC, at the highly stressed
wedges of the ICS and at the contact areas of TFMC,
ICS and LCT. Twenty-four displacement transducers
monitored the elongation of the joint area connecting
adjacent double pancakes of the winding and
the overall distortion of the shape of TFMC and the
change of mutual position (details are presented in
Section 8).
3.7.4. Flow rate and pressure drop sensors
The helium flow rate was measured by Venturi tube
flowmeters Pancake DP1.1 and pancake DP1.2 were
provided with individual Venturi flowmeters and pairs
of capillaries for pressure drop measurements, because
these were the pancakes foreseen for the heat slug injection
to investigate the operation limits of the TFMC.
There were another six Venturi flowmeters installed at
the inlet points of the remaining double pancakes and
bus bars.
3.7.5. Magnetic field sensors
In the geometrical center of TFMC, a pair of Hall
probes and pick-up coils were installed to measure the
magnetic field of the coil.
3.7.6. Heaters at the inlet pipes of the DP’s 1.1
and 1.2
In order to make it possible to heat the helium flowing
into the two pancakes adjacent to the LCT coil the
corresponding inlet pipes were equipped with resistive
heaters with a maximum power of 1000 W.
3.8. Summary
The specific manufacturing technology for the ITER
TF coil design was successfully developed by the construction
of the ITER TFMC. The main effort was
put in the fabrication of the radial plates and the specific
manufacturing technologies related to heat treatment
and the brittleness of the Nb3Sn conductor. The
milling of the groves as well as radial plate flatness
within the small tolerances was a challenging task,
which was solved. The “wind–react–insulate–transfer”
method was the solution for handling the sensitive
conductor without causing any degradation. Tolerance
problems between the reacted conductor spiral
and the groove of the radial plate were solved. All
joints had to be fabricated with the reacted conductor.
This was no problem with the applied joint technology.
Soldering and EB welding techniques were
used joining the special prepared conductor end of
the pancakes with each other. The insulation system
was based on fibreglass–Kapton tapes wrapping with
a three step vacuum impregnation including the fixture
of the winding pack in the thick-walled stainless
steel coil case. The assembling of the TFMC
with the inter-coil structure, which was manufactured
by another company, was performed at the
TOSKA site. The coil was equipped with an electrical,
thermal-hydraulic, and mechanical instrumentation,
which was integrated in the manufacturing steps
of the TFMC.
The whole manufacturing process was accompanied
by quality assurance procedures guaranteeing the quality
of the product in respect of its electrical, thermalhydraulics
and mechanical properties.
The manufacturing of the TFMC was a coordinated
task under the leadership of EFDA between the indus-