Can magnetic islands in an FPP be automatically stabilized by RF condensation?

An experiment was recently conducted at DIII-D to study the “RF condensation” effect, in which EC power deposition and current drive are nonlinearly concentrated at the O-point of magnetic islands. This could lead to more efficient stabilization of large islands in future FPPs. A large n = 1 magnetic island was induced in a low-density plasma, locked at a phase where ECE measurements intersects the island O-point. Then, four gyrotrons were scanned over a range of poloidal launch angles (corresponding to radial deposition location) at full and half duty cycles. ECE and ECEI data were collected and used to determine the temperature perturbation inside the locked island for each poloidal launch angle. Here, we compare the results with predictions from the OCCAMI code, which computes nonlinear temperature perturbations for realistic EC heated islands. We also discuss how the results of this experiment can be applied to improve the OCCAMI code for future studies of this effect.