Decades of global, government-sponsored research in fusion science have established the tokamak-based reactor as the highest performing approach to fusion. In the past, tokamaks have had to be enormous in size to produce net energy from fusion. Commonwealth Fusion Systems (CFS) is using revolutionary superconducting magnets developed in collaboration with MIT to construct smaller and lower-cost tokamak fusion systems.
     CFS is currently developing a tokamak device called SPARC. The company is working to demonstrate the critical fusion energy milestone of producing more output power than input power for the first time in a device that can scale up to commercial power plant size. However, this achievement will only be possible if the plasma doesn’t melt the device.
     Researchers from CFS and Oak Ridge National Laboratory (ORNL) have collaborated on fusion boundary research through a series of projects. These projects include ORNL Strategic Partnership Projects and Laboratory Directed Research and Development projects, work under the Innovation Network for Fusion Energy (INFUSE) program, and other work in partnership with General Atomics.
     Throughout this collaboration, ORNL has developed the simulation capabilities that are necessary to address critical and time-sensitive design issues for the SPARC tokamak.
     The study was published in Nuclear Fusion. It evaluated actuator configurations, in particular those used to control neutral gas flowing in and out of the tokamak.
     A power-producing fusion plasma reactor must reach a temperature at its center hotter than the core of the Sun. At the same time, it must maintain a temperature at the edge of the plasma that is cool enough to avoid vaporizing the fusion device.
     New studies have found that using louvers at the bottom of the fusion device create local conditions that can reduce the temperature of the edge plasma. The louvers permit the hot plasma to “detach” from the walls of the device, spreading out the heat.
     In order to predict the actuators’ ability to control the plasma, ORNL developed new methods to execute a major simulation code, SOLPS-ITER, in a dynamic, time-dependent manner, focused on the actuator design.
     The SOLPS-ITER code models plasma and neutral transport in the boundary region of fusion devices. It has been used to design plasma-facing components for many tokamaks, including the multinational ITER device under construction in France.
     This new dynamic simulation goes beyond standard steady-state models and was developed in a staged manner. First, it considered only plasma transport for predictive control. Next, the response of neutral particles to louver actuators was added. Finally, a fully coupled dynamic model was developed.
     The CFS team used this information from their simulation to zero in on the simplest and least expensive actuator and diagnostics options from a large number of options. This effort enables fusion energy scientists to better control tokamak devices.
     The results of this study indicate a new path for handling this extreme heat, bringing researchers one step closer to a commercial fusion energy source. The study utilized a new simulation capability that accelerates work on whole-device modeling and helps inform researchers about the systems that will control the SPARC plasma.
In addition to the SPARC tokamak project, CFS is working on its successor, the ARC power plant, to supply power to the electric grid.

Commonwealth Fusion Systems