One of the most challenging problems with potential fusion reactors is how the plasma is confined. The plasma is contained by a magnetic field which keeps it away from the machine walls. The combination of two sets of magnetic coils – known as toroidal and poloidal field coils – creates a field in both vertical and horizontal directions, acting as a magnetic ‘cage’ to hold and shape the plasma. Over many years, fusion scientists have been perfecting the magnetic containers that hold the hot plasma while they apply the energy needed to sustain the fusion reaction.
The most successful design, the tokamak, uses a toroidal or donut-shaped chamber surrounded by strong electromagnets. The main components in a tokamak are the magnet system, external heating and drive system and the divertor system. The magnet system is used to generate the magnetic field used to confine the plasma. The external heating system, which can consist of ohmic, RF, and neutral beam heating, raises the plasma temperature to a level needed to initiate fusion reactions.
The divertor must be designed to withstand not only normal operations but also events known as disruptions. These disruptions generate hundreds of thousands of amps of eddy currents within milliseconds that in turn create high Lorentz forces. Such forces determine the size and strength of the support plates, the connections and the actively cooled plasma-facing armour.
Opera has been used extensively in the design of tokamaks, with simulations of both normal operations and disruptions. Forces can be calculated during the disruption and passed to the stress solver for instant design feedback.
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Courtesy Sandia National Labs