In many ways, a fusion reactor is passively safe; most off-normal events within such a device produce a naturally occurring behavior that leads to the calm shutdown of the fusion reaction without operator intervention. One outlier off-normal event is the formation of a relativistic electron beam, which is a very high-energy electron beam capable of causing significant damage to reactor walls.
A concept to passively disperse these high-energy electrons before they build up a large beam is to perturb their orbits by applying a magnetic field. To make this response passive, a conducting coil can be installed inside the reactor. Without any power supply connection, this coil is energized by the initial relativistic electrons during early formation of the beam. The resulting magnetic field then disturbs the electron orbits, causing them to be lost before the beam reaches appreciable energy levels.
In this newly published work from Alexander Battey and colleagues, they unveil a new modeling tool for designing these coils. Taking into account the vacuum vessel of the device, the appropriate positioning and winding path of the coil can be determined. Furthermore, the expected effect on relativistic electron beams is simulated, ensuring that the optimum coil has been designed.
Over the next few years, we will see these coils installed in both the DIII-D tokamak and the SPARC tokamak of Commonwealth Fusion Systems. Experimental demonstration in research devices is an important step to designing a Fusion Pilot Plant and the reactors that follow.
This work was led by Columbia University with co-authors from the Plasma Science and Fusion Center at MIT, General Atomics, and Commonwealth Fusion Systems.
A.F. Battey, et al., Nuclear Fusion 64, 016010 (2024), https://dx.doi.org/10.1088/1741-4326/ad0bcf