Speaker
Description
With the era of burning fusion plasmas approaching, the importance of a thorough understanding of fast-ion physics has never been greater [1]. Burning plasmas are characterised by being predominantly self-heated through the transfer of energy from the fast alpha particles born in fusion reactions to the bulk plasma via collisions. Thus, fast ions will form an integral part of future burning fusion reactor plasmas. Furthermore, fast ions have been found to drive instabilities in the plasma, thus deteriorating mainly their own confinement [2,3]. On the other hand, they are also thought to generate zonal flows, which reduce turbulent transport, and thereby improve the plasma confinement [4]. Measurements of fast-ion distribution functions are essential to enhance the knowledge basis on their role in fusion plasmas. However, reconstructions of fast-ion distribution functions from diagnostic data can only be achieved by solving an ill-posed inverse problem. In this talk, we will give an overview of the efforts made to date in reconstructing the fast-ion distribution function in tokamaks, both in velocity space parametrised locally in (R,z), and in the global orbit space. In addition to this, we will discuss the possibility to determine the distribution function of lost energetic particles by inversion of scintillator-based loss detector measurements. In the process, we will examine the role previous and currents efforts can play in future burning plasmas, including which types of physical constraints and theoretical models are available to serve as prior information in such scenarios.
References:
[1]: Salewski M. et al 2025 Nucl. Fusion 65 043002
[2]: Heidbrink W. W. And White R. B. 2020 Phys. Plasmas 27 030901
[3]: Todo Y. 2019 Review of Modern Plasma Physics 3 1
[4]: Mazzi S. et al 2022 Nature 18 776-782
