Inline ECE measurements for NTM control on ASDEX Upgrade

The successful use of a tokamak for generating fusion power requires an active control of magnetic instabilities, such as neoclassical tearing modes (NTMs). Commonly, the NTM location is determined using electron cyclotron emission (ECE) and this is used to apply electron cyclotron heating (ECH) on the NTM location. In this paper, an inline ECE set-up at ASDEX Upgrade is presented in which ECE is measured and ECH is applied via the same path. First results are presented and a means to interpret the measurement data is given. Amplitude and phase with respect to a reference magnetic signal are calculated. Based on the amplitude and phase, the time of mode crossing is determined and shown to compare well with real-time estimates of the mode crossing time. The ECH launcher and flux surface geometries at ASDEX Upgrade, which are optimized for current drive by a beam path that is tangential to the flux surface near deposition, make it difficult to identify the mode crossing without inline ECE launcher movement. Therefore, NTM control based on inline ECE requires launcher movement to determine and maintain a reliable estimate of the NTM location.