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

will be later supplied from outside. The NBI ports as well as
the port for the diagnostic injector need to be protected
against energetic particles by graphite tiles right from the
beginning on. Due to the spatial constraints these areas need
a sophisticated design. Design studies for both areas have
been started.
3.5.4 Cryo-pumps
Ten cryo-pumps are located behind the target plates and
allow increasing the pumping capacity for hydrogen and
deuterium up to 75 m 3 /s during high-density plasma discharges.
The cryo-pumps are composed of a cryo-panel
cooled with single phase helium, a Chevron baffle cooled with
liquid nitrogen and an additional water cooled baffle. Fabrication
of the cryo-pumps is well advanced (see figure 11).
Figure 11: Main parts of a cryo-pump unit
The cryo-pumps will be installed only after the first operation
phase. Hence fabrication activities were slowed down
and are now only continued in the Garching workshops on a
fill in basis. According to the original design the two pumping
units behind a divertor target would be integrated as one unit
together with the interconnecting cryo-line during assembly
of the plasma vessel. This would have allowed performing a
cold leak-test of the whole unit outside W7-X before assembly.
Since the pumping units shall now be assembled at a
later stage the cryo-line must be separated to allow insertion
of the units into the plasma vessel through a port opening
and joining the cryo-line inside the plasma vessel.
3.5.5 Control coils
Ten control coils will be installed behind the baffle plates.
These coils will be used to correct small field errors at the
plasma edge, to optimize the position and extent of the islands
and dynamically sweep the power across the target plate.
Wendelstein 7-X
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The coils are supplied by the company BNG. Each coil is
made of eight turns of a hollow copper conductor and is
water cooled. By the end of 2007 all ten coils have been
manufactured and six coils have been tested and accepted
(see figure 12). The first two coils have been delivered to
Greifswald and will be used for assembly trials and a test of
the power supply units.
Figure 12: Functional test of a control coil with integrated current leads
3.5.6 Supply lines inside the plasma vessel
Cooling of the in-vessel components is provided from the
main water system through 80 supply ports in the different
W7-X modules. The interface between the supply lines and
the cooling loops inside the plasma vessel is realised by
plug-ins. The water cooling loops inside the plasma vessel
comprise a very complex network with a total length of
about 4000 m. Routing of the water pipes has to consider the
3D-shape of the plasma vessel, pass around a high number
of port openings for diagnostics and heating systems, take
into account the restricted space behind the wall protection
panels, and identify appropriate attachment points. In addition,
the design of the cooling circuits has to consider many
interfaces with the diagnostics and heating systems. The
detail design of the pipe work is supported by manufacture
and trial assembly of full-scale prototypes of the cooling
loops. First prototype loops have been manufactured by IPP.
Assembly trials are performed in a wooden mock-up of the
plasma vessel which was moved from Greifswald to
Garching.
3.6 Refrigeration System
The refrigeration system has an equivalent peak power of
7 kW at 4.5 K to supply the magnet system the thermal
shields, the current leads and the cryo-pumps with helium
at different temperatures and pressures. Linde Kryotechnik
AG is in charge of the delivery of the helium refrigerator.