PhD defense Maria Morbey: Deuterium Dynamics in Lithium Layers: Retention and Release Under Fusion Relevant Plasmas

On 9 July 2025 Maria Morbey Affonso Demitrion Cunha will defend her thesis called 'Deuterium Dynamics in Lithium Layers: Retention and Release Under Fusion Relevant Plasmas'.

• 1e Promoter: dr. T.W. Morgan
• 2e Promoter:  prof. dr. N.J. Lopes Cardozo
• Co-promotor: dr. B. Tyburska-Pueschel

Summary

Nuclear fusion is the process that powers stars, including the Sun, where hydrogen iso-topes, deuterium and tritium, fuse to form helium and a neutron releasing immense energy. On Earth, generating energy through controlled nuclear fusion offers the promise of an inherently safe and sustainable energy source. One of the conditions required for efficient fusion reactions involve heating the fuel, deuterium and tritium, to temperatures exceeding 150 million ◦C. At these temperatures, the fuel consists of ionized particles in a state of plasma. The other two conditions are achieving a sufficiently high fuel density and ensuring that the charged particles are confined long enough to undergo fusion before escaping. The most mature method to achieve this confinement is through a magnetic cage. The leading concept for magnetic confinement fusion is called the tokamak.

Although the particles are confined by the magnetic field, due to diffusion and turbulence, eventually particles still escape their cage, and interact with the solid walls. The magnetic geometries can be chosen such that the impact of plasma-wall interactions on the plasma and wall is minimized, this is done by creating a so-called "diverted" plasma, which guides the escaping particles to a remote region of the wall called the divertor. This magnetic geometry increases the neutral pressure near the wall intersected by the plasma, which reduces the temperature of the ions reaching the wall. As a result, both the erosion by sputtering and the transport of eroded material from the wall to the plasma center are reduced. It also enables access to a regime of higher pumping efficiency of thermalized fusion by-products, which otherwise can dilute the plasma and reduce the fusion output. However, this magnetic geometry causes the plasma to interact with the wall in a very small region, known as the strike point, which means that the unabated power and particle density in this region are extremely high. To ensure the success of fusion reactors, the materials used in the divertor must be able to withstand these high heat and particle fluxes while minimizing their impact on the plasma itself. The material used for these plasma-facing surfaces must also demonstrate low erosion rates, the ability to handle heat loads without degrading, and acceptable impact on tritium inventory. Tritium is a radioactive material with a 12.3-year half-life, therefore it is not naturally occurring on Earth. To overcome this problem, it has long been envisioned that tritium will be produced within the fusion reactor in a component called the breeding blanket. To sustain a continuous reactor operation, it is vital to maintain the breeding ratio (rate of fusion reactions to the number of new tritium atoms produced) significantly above unity. Significant losses of tritium to the wall surfaces can adversely affect this ratio.