U.S. Team Proposes New In-Situ Cleaning Method for Porous Tungsten Walls in Fusion Devices

Researchers from the U.S. Department of Energy's Princeton Plasma Physics Laboratory, Princeton University, and Pennsylvania State University have proposed an in-situ cleaning method for fusion system wall materials, which uses heating combined with neon plasma to remove contaminants from the surface of porous tungsten materials after components are installed and sealed within a vacuum chamber. The research findings have been published in *Nuclear Materials and Energy*.

Image credit: Kyle Palmer / PPPL Communications Department

Fusion system walls must withstand extreme temperatures. Liquid lithium is considered a promising wall protection material, which can be retained within porous tungsten wall tile structures much like water absorbed by a sponge. However, such porous tungsten materials are prone to residual impurities such as carbon, oxygen, and nitrogen during advanced manufacturing processes; when they come into contact with liquid lithium, carbon and oxygen may react to form solid substances that clog pores and impede liquid lithium flow. Even if the material is cleaned at the end of manufacturing, exposure to air during installation can lead to re-contamination.

In the experiments, researchers placed highly contaminated porous tungsten samples into the "Liquid Lithium Tokamak Experiment-Beta" (LTX-β) device at the Princeton Plasma Physics Laboratory. This device is used to study the effects of liquid lithium on plasma and plasma-facing materials. The samples first underwent neon glow discharge treatment inside the device, followed by heating to approximately 800 degrees Celsius. The experiments showed that the cleaning effect of heating combined with neon plasma was significantly superior to using plasma alone.

The researchers reported that the appearance of the treated samples changed from dark gray to metallic silver. Analysis results showed that the proportion of clean metallic tungsten on the sample surface increased from 0 to 87%, with a significant reduction in carbon content. Project lead Camilla Lopez Perez stated that this research provides a framework for cleaning porous tungsten components inside fusion systems, helping to reduce the limitations that material contamination imposes on liquid lithium applications.

The research team chose neon over gases such as helium because neon charged particles are heavier, making them more effective at dislodging impurities like carbon and oxygen. The team also upgraded the probe used to hold and measure samples, enabling it to accommodate thicker samples and concentrate the heating process more directly on the sample itself, thereby improving measurement accuracy.