Abstract
In COMPASS tokamak, the ordinary mode (O-mode) microwave reflectometry diagnostic has been equipped with an upgraded acquisition system and dedicated computational node running the Multi-Threaded Application Real-Time executor (MARTe). This upgrade aims at the deployment of a real-time (RT) plasma position reflectometry (PPR) diagnostic system for future application in closed-loop plasma position control experiments. The system is synchronized with COMPASS MARTe main controller slow cycle, running at 500 μs, and allows a maximum measurement delivery latency of 450 μs. The RT signal processing algorithms, used to reconstruct the O-mode density profiles are the most time consuming step in the control cycle. This is due to the computation of a large number of Fast Fourier Transforms (FFT) over long data arrays, produced for each reflectometry profile measurement. MARTe is a software control framework that allows the integration of external C/C++ libraries and code such as the FFTW3 C library, a highly optimized and performant implementation of the FFT algorithm into the real-time designs. The framework also provides a set of tools to handle the execution of parallel threads, which can be used to expedite the execution of computationally demanding signal processing algorithms. Herein, we present the processing architecture implemented for the multi-threaded reflectometry density profile reconstruction on MARTe framework, using the FTTW3 library. Consistent systematic results have shown that the implemented solution satisfies COMPASS slow control cycle maximum data latency requirement. Moreover, the obtained reduced latency opens the possibility to either increase the number of processed measurements, leading to a more robust plasma position estimate or even to provide multiple position measurements during each control cycle.