X-ray deposition in inertial fusion graphite and silicon-carbide first walls

First wall protection against X-rays and debris coming from the pellet explosion is a critical design issue in inertial confinement fusion reactors. In the present communication, energy deposition of typical target X-ray in silicon-carbide and graphite is shown to occur over distances of the order of the first wall thickness for hard X-ray (γ-ray) target spectra, and the resulting maximum instantaneous temperature rise is negligible. It is also shown that, for photons with energies above 1 keV, large fraction of the target photon yield is deposited behind the first wall. Based on these results, it is concluded that target X-ray (γ-ray), which represent serious design constraint with metallic first walls, may be of less concern with first walls made of silicon-carbide or graphite. Consequently, the first wall protection scheme, based on silicon-carbide or graphite, needs to deal with potential first wall damage due to target debris only