Runaway Electron Imaging Spectrometry (REIS) at the Frascati Tokamak Upgrade (FTU)

A portable Runaway Electron (RE) Imaging and Spectroscopy System (REIS) has been developed at the FTU for the measurement of synchrotron radiation spectra from runaway electrons in tokamaks. The camera is provided with a wide-angle optical system to collect RE synchrotron radiation from different portions of the plasma, two diametrically opposite poloidal cross sections corresponding respectively to the RE backward and forward emission. Part of the collected radiation is optically transmitted to two visible (Ocean Optics HR2000+) and one infrared (Ocean Optics NirQuest 256 High Resolution Near-Infrared) spectrometers through an incoherent bundle of fibres, with a spectral range that spans from 300 nm to 2000 nm. The Toshiba CCD color micro head camera captures the RE synchrotron radiation with a rate of 35 frames per second. The entire system is supervised and managed through a dedicated LabVIEW program that synchronizes, through an external time trigger, and acquires the data of the three spectrometers every 25ms (configurable down to 10ms). The paper gives an overview of REIS and its acquisition system and presents measurements performed in FTU runaway discharges.