A heuristic model for the effects of real-time boronization

Boronization by solid boron injection (SBI) has been shown effective in improving operation of tokamaks and stellarators. However, a quantitative prediction of the amount of B required on nextstep fusion devices such as ITER or a Fusion Power Plant (FPP), while critical for tritium management, remains elusive. We propose a 0-D heuristic model to interpret and predict the

evolution of wall conditions in response to SBI. The model assumes that B introduced in the vessel passivates with plasma operation and that only non-passivated, “active”, B is responsible for wall improvements. The wall conditions are expressed in terms of observables such as brightness of impurity lines, radiative losses, neutral pressure or wall fueling, whose changes are assumed proportional to the variation of active B. DIII-D datasets featuring multiple series of plasmas with phases of B powder injection are reproduced reasonably well, allowing to estimate the growth/decay times of improvements associated with B injection. The decay timescales, expressing plasma operation as integrated heating power, are found in the range of 50-80 MJ for real-time boronization by powder injection.