Some results on the evolution of microstructure for pulsed beam irradiation

Abstract

Studies relating to the development of microstructure using pulsed electron and cyclotron beams are very useful in understanding damage effects in pulsed fusion reactors. In this paper we give some exact results to link the evolution of micro-structure during pulsing with that during continuous irradiation, since the effects in the latter case are relatively well understood. Two pulsing time regimes are considered: pulsing times (a) smaller and (b) larger. than microstructural evolution time constants. In both these cases the adiabatic approximation can be used to decouple the point defect variables from the microstructural variables. In case (a) for pulsed electron irradiation and for relatively small pulsing times in cyclotron irradiation the evolution of the microstructure can be exactly simulated by continuous irradiation using an appropriately determined dose rate. A similar analysis is made for case (b) and several effects encountered in continuous irradiation are shown to manifest themselves in pulsed irradiation. A general formalism is developed to determine the equivalent continuous irradiation parameters like dosc rate which will simulate the microstructural development under pulsing. Our treatment is semiquantitative and is based on the analysis of the trajectories in the phase space. The results presented provide a simple practical approach for interpreting and understanding experimental observations.