The spatial structure of electron temperature fluctuations observed by ECE imaging in the Large Helical Device*

Electron Cyclotron Emission Imaging (ECEI) is a powerful tool for obtaining the spatial structure of MHD or other instabilities. In the Large Helical Device (LHD), the ECEI system in V-band and Q-band has been developed for low magnetic field (1.0 - 1.375 T) experiments [1, 2]. The system has 192 (8-vertical × 24-radial) channels, providing a two-dimensional structure of electron temperature and its fluctuations. Fluctuations of ECE signal associated with energetic particle-driven GAM and MHD modes are successfully obtained in LHD plasma. By analyzing 2D images, the time evolution of the spatial structure of fluctuations can be obtained. In the presentation, we will introduce the ECEI system on LHD and discuss the spatial structure dynamics of electron temperature fluctuations extracted from ECEI images with observations of other diagnostics, such as magnetic probes.

[1] H. Tsuchiya et al., Plasma Fusion Res. 13, 3402063 (2018)  [2] Y. Goto et al., JINST 17 C01016 (2022)