For fusion plasma-facing applications, the most essential properties are thermal conductivity, strength and ductility, thermal shock and thermal fatigue resistance, structural stability at elevated tem­perature, and stability of the properties under neu­tron irradiation. The advantages and disadvantages of tungsten for these conditions are manifold and opposed to each other as shown in Table 2. While the advantages of the material are mainly related to its high temperature-handling capability, the limitations are associated with manufacturing and handling at low temperatures (below ductile to brittle transition temperature, DBTT61-63), plasma com­patibility including neutron irradiation, and radio­logical issues.

However, with regard to other potential PFMs, for example, Be (see Chapter 4.19, Beryllium as a Plasma-Facing Material for Near-Term Fusion Devices), CFC (see Chapter 4.18, Carbon as a Fusion Plasma-Facing Material), and Mo, tungsten is still the most promising, offering an advantageous combination of physical properties and, therefore, has become the material of choice for ITER and DEMO. Since this decision was made, R&D efforts for investigating newly developed tungsten grades

Table 2 Features of W armor materials

Advantages Disadvantages

50 mm

(b)

and alloys that are able to overcome or at least miti­gate some of the above-mentioned disadvantages have significantly increased.