‘Louvers’ on fusion device should exhaust gases as hot as a star

Commonwealth Fusion Systems (CFS) is developing a tokamak device called SPARC. The company aims 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 is only 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, including ORNL Strategic Partnership Projects and Laboratory Directed Research and Development projects, work under the Innovation Network for Fusion Energy (INFUSE), and other work in partnership with General Atomics.

Throughout this collaboration, ORNL has developed simulation capabilities required to address critical and time-sensitive design issues for the SPARC tokamak.

The study, appearing in Nuclear Fusion, evaluated actuator configurations, in particular those used to control neutral gas flowing in and out of the tokamak.

A power-producing fusion plasma 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 plasma edge that is cool enough to avoid vaporizing the fusion device.

New studies have found that using louvers at the bottom of the fusion device, like those found on the air ducts of a home, create local conditions that can reduce the temperature of the edge plasma. Specifically, the louvers allow the hot plasma to “detach” from the walls of the device, spreading out the heat.

To predict the actuators’ ability to control the plasma, ORNL developed new methods to run 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 and has been used to design plasma-facing components for many tokamaks, including the multinational ITER device under construction in France.

This new dynamic simulation capability goes beyond standard steady-state models and was developed in a staged manner, first considering only plasma transport for predictive control, then the response of neutral particles to louver actuators, then finally a fully coupled dynamic model.

The CFS team then used this information to zero in on the simplest and least expensive actuator and diagnostics options from a large number of candidates. This work enables fusion energy scientists to better control tokamak devices.

The results of this study show a new path for handling this extreme heat, bringing researchers one step closer to a fusion energy source. The study used a new simulation capability that advances work on whole-device modeling and helps inform researchers about the systems that will control the SPARC plasma.

In addition to the SPARC tokamak, CFS is planning its successor, the ARC power plant, to put power on the electric grid.