Speaker
Description
Electron Cyclotron Emission (ECE) is a widely used diagnostic technique in tokamaks as a 1D measurement of electron temperature along a line of sight, with high spatial and temporal resolution. The low-field side (LFS) ECE in TCV uses heterodyne radiometry to downconvert the mm-wave emission (centered around 80 GHz) to an intermediate frequency (IF) signal (2-20 GHz), which is then split into 24, 750-MHz wide channels using bandpass filters of varying frequency before acquisition. This contribution will describe an alternative, fast-acquisition method, which consists of directly acquiring the IF signals and using software-based FFT methods to emulate the physical LFS ECE radiometer. This is done using an analog-to-digital (ADC) converter with an ultra-fast sampling rate of 32 GS/s and an analog front-end bandwidth of 10 GHz, short of the theoretical Nyquist frequency of 16 GHz. The major strength of this method lies in the post-processing. With a digital radiometer, the number of channels, bandwidth, spatial resolution, and temporal resolution, among other parameters, can be varied at will in the analysis of a given shot. This method has been successfully benchmarked against the LFS ECE in TCV, and will be used alongside it for turbulence studies in particular. Methodology and applications on turbulence measurements will be presented.