Integrated package of electron cyclotron emission imaging data processing and forward modeling in OMFIT.

An Electron Cyclotron Emission Imaging (ECEI) data analysis module has been developed for the OMFIT platform to accommodate the needs of users at the DIII-D tokamak for physics applications. The user can easily access the ECEI spatial observation windows in the plasma that are calculated based on the automatically retrieved hardware setup and available DIII-D equilibria, perform spectral analysis, and obtain 2D electron temperature fluctuation images. The module provides a powerful data post-processing package for extracting important physics parameters from the 2D measurements, including the radial structure and poloidal mode number of Alfven eigenmodes, as well as the frequency-vs-wavenumber dispersion relationship of broadband MHD. The module propagates characterized synthetic fluctuations for the user, so one can perform forward modeling tasks with simple analytical fluctuations.

Radio frequency measurements of energetic-particle-driven emission using the ion cyclotron emission diagnostic on the DIII-D tokamak.

The Ion Cyclotron Emission (ICE) diagnostic on the DIII-D tokamak consists of two outboard midplane systems. In the first system, straps of an ion cyclotron range of frequencies antenna are configured as receiving antennas. For the second system, dedicated magnetic probes incorporated into the outer wall of carbon tiles have recently been restored. These systems collected a large set of radio frequency measurements in the 2015-2018 experimental campaigns by digitizing signals at 200 MSamples/s for ∼5 s per discharge. Each shot typically yields 32 GB of data; techniques for successful handling and analysis of this challengingly large dataset are discussed. The raw voltage fluctuations (<0.2 V and <1 mW) are analyzed in frequency space via fast Fourier transforms. Signals can be analyzed between 1 and 200 MHz with appropriate filtering and aliasing; this frequency range is limited by DC breaks used to provide 5 kV DC isolation. These high-frequency signals are driven by energetic ions and electrons. In particular, energetic-ion-driven ICE occurs at harmonics of the ion cyclotron frequency, enabling the frequency to be mapped to lab space via equilibrium reconstruction. In many DIII-D plasmas, ICE is emitted from the radial center of the plasma.