The ITER toroidal field model coil project

214 A. Ulbricht et al. / Fusion Engineering and Design 73 (2005) 189–327
Fig. 4.9. Energising both coils to the maximum current of 49.5 kA in the TFMC and 11.3 kA in the LCT coil with a LCT coil winding operation
temperature of 4.5 K.
found during the evaluation phase and is included in
Section 4.5.2.
After a high voltage discharge from 6.3 kA, the recooling
energy was 403 kJ, which is 75% of the stored
energy (Fig. 4.11). In this case the efficiency of the
energy extraction is poor because the time constant of
the discharge circuit (∼27 ms) is much lower than the
time constant of the structure (radial plates and case
∼100 ms).
4.3.2.2. Simultaneous operation at two temperature
levels, 3 and 4.5 K. At the temperature level of 4.5 K,
the LCT coil could be energised up to 11.3 kA only,
but according to the test program an operation up to
16 kA was required and for this a cooling temperature
of the LCT coil winding down to 3.5 K was necessary.
Steady state operation up to 16 kA was performed
without problems at 3.5 K but two quenches occurred
in the LCT coil during cycling current operation of
the TFMC. It was found that the temperature margin
was too small and as a consequence the operation
temperature was reduced to 3 K for the further test
runs. For an operation at reduced temperature (3 K),
the 500 W refrigerator was used as mentioned above
and explained in [53]. The operation in this mode is
not automated and it was therefore only possible dur-
ing daytime with operators present. The consequence
was that the cool down from 4.5 to 3.5 K, respectively,
3 K as seen in Fig. 4.12 had to be repeated every morning.
In Fig. 4.13, temperature, coil current and heat
load profile during the test at the rated coil current of
70 kA in the TFMC and 16 kA in the LCT is shown.
The cooling conditions are listed also in Table 4.4. In
Fig. 4.14, the re-cooling after a safety discharge from
the same coil current level can be seen including the
energy required for the re-cooling. Only 2–3% of the
stored energy was transferred to the cryogenic system
after all the safety discharges and quenches of both
coils together and could be handled without problems.
Most of the energy (97–98%) could be extracted and
transferred to the dump resistor. The cooling requirements
of the TFMC winding versus the coil current are
shown in Fig. 4.15. In this diagram, it can be clearly
seen that there is an additional heat load to the resistive
and standby losses, which is explained in Section 6.1.3
as AC losses in the radial plates caused by the ripple of
the current.
4.3.2.3. Handling of TCS measurement and safety discharge.
In preparation of the TCS measurements a feasible
heating scenario had to be investigated with the
following constraints: