Sophia Henneberg is the Norman Rasmussen Career Development Assistant Professor in the Department of Nuclear Science and Engineering at Massachusetts Institute of Technology. She received her Master’s degree at the University of Wisconsin-Madison, during her Fulbright year in 2012 and received her PhD in Physics from the University of York in 2016. Before coming to MIT Sophia was a permanent research scientist at the Max Planck Institute for Plasma Physics in Greifswald, Germany. During her time in Greifswald, she was the Principal Investigator of the Stellarator Optimization TSVV group which is a collaboration between several European research institutes. She was also the Stellarator Optimization Task Leader of the HILOADS collaboration, which was a US-German collaboration.
A new class of compact stellarator–tokamak hybrid devices offers the exciting potential to combine the advantages of both stellarators and tokamaks into a single system—providing improved stability (disruption avoidance), steady-state operation, and relatively simple coil configurations. Achieving this hybrid configuration requires adding just one type of stellarator coil to the high-field side, alongside conventional tokamak coils. This approach could also open the door to upgrading existing tokamak facilities.
One of the defining features in stellarator design is the feasibility of the magnetic coils—ultimately, these are the components that must be physically constructed. Traditionally, stellarator optimization has focused first on achieving desirable plasma properties, as this task is very challenging in its own right. However, developing strategies that improve coil geometry while simultaneously preserving key plasma characteristics is essential for advancing stellarator design.
The equilibrium and stability of a plasma are critical factors in the success of a fusion experiment, as they directly influence its confinement properties. Stability is typically assessed using Magnetohydrodynamic (MHD) models, which provide a fluid-like description of plasma behavior. If the plasma equilibrium is unstable, any optimization efforts become ineffective. Furthermore, certain instabilities can lead to severe damage or even total destruction of the fusion device, making it essential to prevent them under all circumstances.
The conventional approach to stellarator optimization is often referred to as the “two-stage approach.” In the first stage, the plasma boundary is optimized, with its geometry treated as the independent degree of freedom, in order to achieve key physics objectives such as optimal confinement and stability. The second stage focuses on optimizing the coil design, where the coil geometry is the independent variable. This step ensures that the coil configuration closely matches the desired plasma boundary while adhering to engineering constraints. However, the methods used for optimization, the way we define our independent degrees of freedom, and the expressions we choose for our target objectives can significantly impact the optimization outcome. Refining these approaches, therefore, is crucial for achieving more efficient and effective stellarator designs.