An improved method to evaluate the ideal no-wall beta limit from resonant field amplification measurements in JET

摘要

Modelling the low-n, low frequency resonant field amplification (RFA) effects for JET plasmas, using the MHD code MARS-F, offers explanations to one of the recent observations made in experiments, namely a mismatch between the measured RFA threshold and the predicted no-wall beta limit according to ideal MHD calculations. The mismatch is minimized by applying a new way of determining the RFA threshold, based on evaluating the logarithmic derivative of the RFA amplitude as a function of the normalized plasma pressure. This improved method is shown, at least in theory, to be robust in predicting the no-wall beta limit for JET plasmas.