Abstract
The automatic controller developed for MHD instability control on FTU via the real time (RT) EC launcher [1, 2] is based on the a-priori estimate of the instabilities location and on the fast elaboration of the stream of diagnostic data. A fast data acquisition system, based on existing standard FTU diagnostics, collects thermal and magnetic signals by a 12-channels ECE polychromator [3] and by a set of 22 Mirnov coils respectively. Moreover, the EC time waveform from directional couplers along the transmission line is acquired as well. This set of signals is processed in a timescale significantly shorter than the typical time step of the controller (1ms). RT elaboration algorithms aim at supplying the controller [4] with reliable information about the existence and the spatial location of the instability and about the actual ECRH deposition layer in plasma. The main algorithms blocks are ECE-ECE, ECE-Mirnov and ECE-ECRH cross-correlation, and SVD (Singular Value Decomposition) of Mirnov signals. The capabilities of effective detection, false positive resilience, and mode discrimination will be discussed through the application to actual plasma data.
Highlights
The automatic controller developed for MHD instability control on FTU via the real time (RT) EC launcher [1, 2] is based on the a-priori estimate of the instabilities location and on the fast elaboration of the stream of diagnostic data
The EC time waveform is acquired as well from directional couplers (ECH) along the transmission line ; when modulating the EC power, an estimate of the EC absorption layer can be evaluated, which is complementary to the a-priori estimate evaluated by the RT ray-tracing code [5]
The RT evaluation of the actual plasma surface where the EC power is absorbed is performed via a lock-in technique, that is by modulating the RF power sources, and cross-correlating the thermal fluctuations (ECE) with signals (ECH) coming from two directional couplers placed along the transmission waveguides
Summary
The automatic controller developed for MHD instability control on FTU via the real time (RT) EC launcher [1, 2] is based on the a-priori estimate of the instabilities location and on the fast elaboration of the stream of diagnostic data. The EC time waveform is acquired as well from directional couplers (ECH) along the transmission line ; when modulating the EC power, an estimate of the EC absorption layer (rDEP) can be evaluated, which is complementary to the a-priori estimate evaluated by the RT ray-tracing code [5] The crosscorrelation profiles are referred to the FTU major radius and to a plasma surface (labelled as r in the following) and processed to evaluate whether one or more instabilities are occurring and where instabilities are located into the plasma (rMHD); in case of modulated injection of EC power the estimates of rDEP can be evaluated through ECE-ECH cross-correlation.
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