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VACUUM VESSEL DESIGN | MAGNETIC FUSION ENERGY
FIGURE 2. The ADX vacuum vessel features a unique design with ve separate shells that FIGURE 3. Model geometry, at left, used
are bolted together. to determine the eddy currents in the ADX
vacuum vessel walls, at right.
simulation in COMSOL Multiphysics® magnetic model of the ADX, including 1.5 million amperes of current, stops
software to predict the magnetic elds, the vessel, plasma, and poloidal moving after 10 milliseconds, and loses
eddy currents, and Lorentz forces magnetic coils, which are needed to all of its current in a single millisecond.
resulting from a plasma disruption,” hold the plasma in its Rapidly changing magnetic elds
explains Doody. “The calculated loads equilibrium position. surrounding the disruptive plasma
are then applied to a separate structural produce eddy currents in the vacuum
model of the vessel in order to predict A worst-case scenario exists vessel shell. Lorentz forces are exerted
stress and displacement.” Figure 3 shows for plasma disruptions in vertical on the vessel when the eddy currents
the geometry for a cyclic symmetry displacement events (VDE), where cross both the poloidal magnetic elds,
the plasma drifts upward carrying and the stronger toroidal magnetic
FIGURE 4. At top, the geometry for the structural model of the ADX shows purple boundaries elds of the tokamak that con ne
where the structure is xed. Stress and displacement simulation results indicate the design the plasma.
requires reinforcement. At bottom, the model geometry shows an additional xed boundary
corresponding to a support block added to the ADX design. During a VDE, eddy currents are
larger in magnitude because of how
close the plasma gets to the vessel wall,
and VDE is therefore the test case of
choice in the computational model
of the ADX. Figure 3 shows the eddy
current distribution calculated from the
numerical model. A second model was
developed to determine the Lorentz
forces due to the toroidal magnetic
elds of the tokamak, where only
poloidal elds were included in the rst
model of the ADX.
ð STRENGTHENING THE
ADX VACUUM VESSEL
Plasma disruptions result in strong
Lorentz forces that act on the walls of
the ADX, particularly in the upper and
lower pockets of the vacuum vessel
during a VDE. In a structural model
of the ADX vessel, shown in Figure 4,
the top and bottom boundaries are
attached to the vessel cover and cannot
be displaced during simulation. Loads
corresponding to the Lorentz force
exerted on the vessel are applied to the
30 COMSOL NEWS 2016
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