Controlled thermonuclear reactor first wall sputtering and wall life estimates

Abstract

Equations and graphs are developed for rapid estimation of sputtering rates at the first wall of controlled thermonuclear reactors (CTR). High-energy particle sputtering yield data and potential particle fluxes are presently not readily available for most materials and many reactor designs, thus the equations were set up to provide rapid estimation of sputtering effects when data become available. Limiting wall sputtering-yield-particle-flux products were determined according to the equation ΣSμφμ < Kd(t′)/t′, where Sμ and φμ are the sputtering yield (atoms/particle) and flux (particles/cm2 sec) of bombarding species μ, d(t′) is the allowable wall thickness removal (in cm) in t′ years, and K is a material constant. K varied little (from 1.36×1015 to 3.28×1015) for the wall materials considered (V, Mo, Nb, Ta, Zr, stainless steel, and Al2O3), so that a conservative estimate for the limiting sputtering-yield-particle-flux product is 1015 times the allowable sputtering rate in cm/yr. The sputtering yield in molecules per particle given for compounds such as Al2O3 must be multiplied by the number of atoms in the molecule to satisfy this relationship. Use of the equations to estimate wall sputtering of pulsed (high-β) and steady-state (low-β) reactors indicated that sputtering rates will be sufficiently high that they cannot be ignored. Factors reducing sputtering erosion rates, such as surface roughness, impurity effects, and sputtered material redeposition, are discussed.