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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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