2024 EPS Hannes Alfvén Prize

Long citation

Professors Tünde Fülöp and Per Helander have significantly advanced plasma theory through a number of fundamental contributions. Their research spans many topics including runaway electrons, kinetic instabilities and transport processes in magnetized plasmas. By pinpointing key physical mechanisms, they have catalyzed innovative developments in experimental devices for nuclear fusion applications.

Professor Tünde Fülöp has been a leader in the field of disruptions and relativistic “runaway” electrons associated with these events. She has systematically explored the physics of runaway electrons in tokamaks and beyond, and conducted unprecedented modelling efforts applicable to both existing experiments and future devices. As part of this endeavour, Professor Fülöp has investigated various facets of the problem, including runaway-electron-driven electromagnetic instabilities, the impact of different collision types, radiation reaction effects, and the role of partially ionized impurities on runaway electron dynamics. Additionally, she has evaluated and optimized disruption mitigation strategies involving external magnetic perturbations and massive material injection. Furthermore, Professor Fülöp has played a crucial role in overseeing the development of several open-source, state-of-the-art runaway modelling tools and synthetic diagnostics. These tools have gained widespread use in the scientific community, reflecting her commitment to advancing collective knowledge in the field.

Professor Per Helander has obtained seminal results in the theory of stellarator plasmas by systematically exploring the question of how the properties of magnetically confined plasmas depend on the geometry of the magnetic field. In most such plasmas, turbulent transport caused by micro-instabilities arising from plasma density and temperature gradients poses a significant challenge. Professor Helander foresaw a crucial development, the absence of the most important density-gradient-driven instability in certain types of magnetic fields. This prediction is believed to underpin the remarkable record plasma performance achieved in the Wendelstein 7-X stellarator. In addressing long-standing concerns about neoclassical impurity accumulation in stellarators, professor Helander demonstrated a possible route to avoiding it in collisionality regimes relevant to reactors. Furthermore, he identified important differences between stellarators and tokamaks concerning plasma rotation. On large scales, it is relatively slow in stellarators and governed by neoclassical processes even in the presence of turbulent transport, and on small scales zonal flows behave differently. These and other revelations have shaped the general understanding of stellarator plasmas and the burgeoning field of stellarator optimization.