Speaker
Description
The fusion plasma research group at the University of Milano-Bicocca has recently expanded its research to the physics of the tokamak edge, i.e. the region between the confined plasma core, where the field lines do not intersect any solid surface, and the plasma-facing components (PFCs). In this contribution, we present an overview of the group’s ongoing activities in this area, starting from the plasma core and moving outwards to the PFCs.
The outermost region of the plasma core is of crucial importance for determining the overall plasma confinement and, in turn, the achievable fusion power in the perspective of a fusion power plant (FPP). In the so-called high-confinement mode (H-mode) [1], currently considered the reference scenario for FPPs, the edge region exhibits a strong reduction of outward transport. At the ASDEX Upgrade (AUG) tokamak, we have correlated the power required to access H-mode with the microscopic shearing of turbulence driven by the E×B drift, itself linked to the ion heating [2]. This connection is currently being further investigated at the TCV tokamak through dedicated experiments, representing one of the first physics-based explanation of the H-mode power threshold.
Further outside, the separatrix, defining the boundary between the confined plasma and the Scrape-Off Layer (SOL), is a key interface region. We performed experiments at ASDEX Upgrade and TCV investigating the ion-to-electron temperature ratio, a critical parameter for confinement predictions, SOL heat flux calculations, and transport characterization, yet still poorly explored. Our results show that Ti/Te is mainly set by global electron and ion heat fluxes from the plasma core, while local effects play only a minor role [3].
Stepping further outward, the plasma-wall contact is usually localised in a dedicated region called the divertor. For reactor conditions, estimated peak heat loads on the divertor exceed material limits and therefore require effective mitigation. A key strategy is detachment, achieved by impurity injection, which radiates most of the heat and forms a recombining plasma layer in front of the PFCs, thus protecting them from direct exposure. In this contribution, we investigate the role of hydrogen molecules in this process and the bifurcating phenomena that arise during the transition to detachment [4].
Finally, to complete the overview, we will outline the group’s involvement in the design, development, and operation of edge diagnostics across different devices.
References:
[1] F. Wagner et al 1982 Phys. Rev. Lett. 49, 1408
[2] M. Cavedon et al 2020 Nucl. Fusion 60 066026
[3] M. Cavedon et al 2025 Nucl. Fusion 65 106007
[4] L Scotti et al 2024 Plasma Phys. Control. Fusion 66 075004
This work has been carried out within the framework of the EUROfusion Consortium, partially funded by the European Union via the Euratom Research and Training Programme (Grant Agreement No 101052200 — EUROfusion). The Swiss contribution to this work has been funded by the Swiss State Secretariat for Education, Research and Innovation (SERI). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union, the European Commission or SERI. Neither the European Union nor the European Commission nor SERI can be held responsible for them. This work was supported in part by the Swiss National Science Foundation.
