Theoretical Study of the Impedance Matching of the Ferrite Tuner System for ICRF Heating

A theoretical study on a ferrite stub tuner antenna system for ion cyclotron resonance frequency (ICRF) heating is discussed in this paper. High amounts of radio frequency power can be reflected at the antenna as a result of impedance mismatches arising from large changes in the plasma resistance during L- to H-mode transitions or edge localized modes. A fast-response ferrite stub tuner network has been proposed to mitigate these reflections by rapidly varying the impedance to match the rapid load changes on the ICRF antenna. This study numerically shows the influence relationship of the normalized mechanical length and the ratio of the ferrite part of two ferrite stubs on the regulating range of a biasing magnetic field of two stubs. A prematching stub can be used to reduce the standing-wave voltage on the ferrite tuners. The analysis of the ideal position and length of the prestub as well as the distance between the ferrite network and prestub are presented. Numerical simulations demonstrate that selecting ideal values for mechanical length and the ratio of the ferrite part of two ferrite stubs plays an important role in the impedance matching performance of the triple ferrite system during a large variation in plasma resistance.