Design and Analysis of the ITER Vertical Stability Coils
Authors: Peter H. Titus, et. al.
Abstract:
The ITER vertical stability (VS) coils have been
developed through the preliminary design phase by
Princeton Plasma Physics Laboratory (PPPL). Final
design, prototyping and construction will be carried out
by the Chinese Participant Team contributing lab,
Institute of Plasma Physics, Chinese Academy of Sciences
(ASIPP). The VS coils are a part of the in-vessel coil
systems which include edge localized mode (ELM) coils
as well as the VS coils. An overview of the ELM coils is
provided in another paper at this conference. 15
The VS design employs four turns of stainless steel
jacketed mineral insulated copper (SSMIC) conductors
The mineral insulation is Magnesium Oxide (MgO).
Joule and nuclear heat is removed by water flowing at 3
m/s through the hollow copper conductor. A key element
in the design is that slightly elevated temperatures in the
conductor and its support spine during operation impose
compressive stresses that mitigate fatigue damage. Away
from joints, and break-outs, conductor thermal stresses
are low because of the axisymmetry of the winding (there
are no corner bends as in the ELM coils).The 120 degree
segment joint, and break-out or terminal regions are
designed with similar but imperfect constraint compared
with the ring coil portion of the VS. The support for the
break-out region is made from a high strength copper
alloy, CuCrZr. This is needed to conduct nuclear heat to
the actively cooled conductor and to the vessel wall. The
support "spine" for the ring coil portion of the VS is 316
stainless steel, held to the vessel with preloaded 718 bolts.
Lorentz loads resulting from normal operating loads,
disruption loads and loads from disruption currents in the
support spine shared with vessel, are applied to the VS
coil. The transmission of the Lorentz and thermal
expansion loads from the "spine" to the vessel rails is via
friction augmented with a restraining "lip" to ensure the
coil frictional slip is minimal and acceptable. Stresses in
the coil, joints, and break-outs are presented. These are
compared with static and fatigue allowables. Design for
fatigue is much less demanding than for the ELM coils. A
total of 30,000 cycles is required for VS design. Loads on
the vessel due to the thermal expansion of the coil and
spine are significant. Efforts to reduce these by reducing
the cross section of the spine have been made but the
vessel still must support loads resulting from restraint of
thermal expansion.
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Submitted to: Neuclear Technology Magazine (August 2012) TOFE 2012 Conference, Nashville, TN (August 27-31, 2012
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Download PPPL-4809 (pdf 274 KB 9 pp)
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