Multiple electron cyclotron power deposition location tracking by break-in-slope analysis in TCV plasmas

Abstract

Modulation of the amplitude of externally injected electron cyclotron (EC) power is a frequent method used to determine the radial power deposition profile in fusion plasmas. There are many tools to analyze the plasma response to the power modulations under quasi-stationary conditions. This paper focuses on the unique ability of the break-in-slope (BIS) method to retrieve a quasi-instantaneous estimate of the power deposition profile at each power step in the modulation, an outcome particularly relevant to track the power deposition location under non-stationary conditions. Here, the BIS analysis method is applied to the signals of a fast and high radial resolution wire-chamber soft x-ray camera in the Tokamak à Configuration Variable (TCV) where the plasma magnetic configuration and thus the EC resonance location are varied during the plasma discharge. As a step to validate this technique before real-time control experiments, the time-varying EC power deposition location of a single beam is successfully monitored by off-line BIS analysis. Simultaneous tracking of deposition locations of two EC beams gives promising results.