Plasma–Wall Interaction

At a glance

As part of the “Plasma–Wall Interaction” topic, Jülich researchers develop and analyse new materials that can withstand the extreme conditions in fusion reactors. They investigate both the physical and chemical processes that take place at the interface between plasma and wall materials as well as the effects of plasma impurities caused by the erosion of wall components, which can lead to plasma quenching.

In addition, the Jülich teams design, build, and operate diagnostic systems to better understand the processes at the plasma edge. Their work is supported by theoretical models, including machine learning and artificial intelligence.

Challenges

The materials that line the inner walls of a fusion reactor have to withstand extreme conditions, including high temperatures, intense neutron radiation, and constant bombardment by high-energy plasma particles. These conditions cause erosion, wear, and structural damage. The erosion of the wall materials in turn leads to plasma impurities that affect the efficiency and stability of the fusion reactions. The inner walls of a fusion reactor must also be able to dissipate immense amounts of heat without being damaged.

In addition, the findings from experimental studies and small test facilities form the basis for large fusion reactors such as ITER and future commercial fusion power plants.

Solutions

Jülich researchers are developing and testing new highly resistant materials, and are investigating the erosion mechanisms of material damage caused by plasma–wall interactions. They use novel diagnostic systems to determine in detail the interactions between plasma particles and wall materials. In this way, they can track down sources of erosion and impurities in the main chamber. As a result, impurities can be minimized and more suitable materials identified.

To remove impurities from the plasma, the Jülich fusion experts designed a “tungsten divertor”. This component is used, for example, to cool and separate helium atoms from the plasma, which are produced during the fusion reaction. Since the component is deliberately exposed to the plasma, which has a temperature of more than 100 million °C, it must be extremely heat-resistant and have an efficient cooling system.

New types of alloys or high-tech composite materials are being tested for this purpose, such as fabrics made of microscopic tungsten fibres woven into yarns and embedded in a matrix of chemically deposited tungsten.

In addition, the Jülich researchers are investigating ways to efficiently recover the tritium fuel absorbed in the walls of the facility, which is essential for the ongoing operation and subsequent decommissioning of fusion facilities. They also conduct research into the effect of neutron radiation on various materials and design new materials that are more resistant to neutron damage. The Jülich High-Temperature Materials Laboratory, which is unique worldwide, provides the necessary infrastructure for this.

To gain a better theoretical understanding, the scientists model the plasma flow conditions, heat transfer, and thermal load on the wall systems. They conduct detailed laboratory experiments and develop advanced simulation models to better understand and control the interactions. At the same time, they create forecasts for the behaviour of the plasma and the materials used in future fusion reactors, and use state-of-the-art supercomputers, machine learning, and artificial intelligence. Together with the Jülich Supercomputing Centre (JSC), the numerical tools are adapted and further developed for various scenarios of plasma–wall interactions.