The ITER toroidal field model coil project

222 A. Ulbricht et al. / Fusion Engineering and Design 73 (2005) 189–327
• Use of SE-Cu in the contact area and in the room
temperature region to reduce the Joule heating.
• Use of clamp contact between the cold end of the
current lead and the bus bar connection.
• Implementation of the so-called “cold gas return”
circuit, which allows to operate the first segment of
the heat exchanger with a higher mass flow rate than
the rest of the heat exchanger.
• Integration of a water cooled flexible jumper cable at
the room temperature end of the current lead to connect
the current lead to the water cooled aluminium
bus bars of the TOSKA facility.
The electrical insulation system of the current lead
is described in detail in [10].InFig. 4.22, a photograph
of the two 80 kA current leads installed in their cryostat
extensions during assembly in the TOSKA facility is
presented. Fig. 4.21 shows an illustrative drawing of
the helium-cooled heat exchanger, including the cold
end clamp contact to the superconducting bus bar and
Fig. 4.22. Photograph of the 80 kA current leads installed in their
cryostat extensions during assembly in the TOSKA facility (1, cryostat
extension; 2, current lead; 3, flexible copper bus bars; 4, bus bar
type 1; 5, bus bar type 2).
the screw connection to the flexible copper bus bars.
Due to the vertical installation of the current leads, the
superconducting bus bar has to be divided in two parts
(bus bars 1 and 2) for assembly reasons having a clamp
contact in between. The cooling scheme is illustrated
in Fig. 4.23.
4.4.2. Overall performance of the current leads
during TFMC operation
As the first aim of the TFMC experiment was to
reach the nominal current of 80 kA, the current leads
were not operated in an optimum way. This was due
to the fact that the experimental optimised operation
parameters of the leads were unknown because no separate
test was possible due to time constraints.
During Phase 1 of the TFMC experiment, and especially
at its end, some parameter studies were made to
find the minimum helium mass flow rates and to identify
the reasons for the higher heat load introduced in
the BB-1/2 system.
4.4.3. Electrical resistances of the clamp contacts
The voltage taps used for quench detection were
used to determine the resistances of the bus bar (+) and
(−) systems. Each of them consisted of one full joint
and two half joints of which one was the clamp contact
to the current lead (Fig. 4.23). Each of the clamped
joints was manufactured in a different way: for joint 2,
indium wires were arranged in the longitudinal direction
and pressed flat by tightening of clamping bolts for
Fig. 4.23. Cooling scheme of the 80 kA current lead bus bar system
(bus bar I = bus bar 1; bus bar II = bus bar 2).