Wall, first

Under normal operating conditions the first wall must handle high plasma surface heat fluxes (Table 1), as well as volumetric heat loadings due to the penetrating neutron and electromagnetic radiation. The volumetric heat loading is dependent... 

Fig. 1. Schematic diagram of the proposed first wall for the ITER reactor.

As discussed in the introduction, disruptions cause the most severe thermomechanical loading experienced in a tokamak. In each of the 500 or so disruptions expected in ITER, approximately 10-20 MJ/m will be deposited onto the first wall in 0.01 to 3 seconds. Such a disruption will cause very high thermal stresses and significant material erosion (Section 4). As these events are transient in nature, the ability of the PFC to withstand the disruption depends on the material s ability to both conduct and to absorb the deposited heat, before reaching a temperature or stress limit. For comparative purposes, a disruption figure of merit takes this into account ... 

As discussed earlier, the first wall materials in next generation machines will receive from 0.005 to 30 displacements per atom. At the lower end of this range (<0.01 dpa) there are essentially no mechanical property changes expected in graphite materials. However, even at these low doses thermal conductivity and stored energy are of concern. For displacement levels >0.01 dpa other property... 

Groner, P., Gimzewski, J., and Veprek, S., Boron and Doped Boron First Wall Coatings by Plasma CVD, / Nucl. Mater., 103(l-3) 257-260(1981)... 

Table 1. Materials and heat loads for the major fusion machines world wide (see Section 1.3 for definitions of divertor and first wall)... 

Fusion Machine Country Fuel System First Wall Heat Load (MW/m2) First Wall Material Divertor or Limiter Heat Load (MW/m2) Divertor of Limiter Material... 

The crystal structure of beryllium carbide is cubic, density = 2.44 g/mL. The melting point is 2250—2400°C and the compound dissociates under vacuum at 2100°C (1). This compound is not used industrially, but Be2C is a potential first-wall material for fusion reactors, one on the very limited list of possible candidates (see Fusion energy). 

The Surface Chemistry of First-Wall Materials in Magnetic Fusion Devices... 

In addition to a spatial variation, the expected plasma flux and consequent plasma-wall interactions on first-wall components... 

---