Speaker
Description
A divertor retarding field energy analyzer (RFEA), for time-resolved local ion temperature (Ti) measurements was tested in the lower divertor of the DIII-D tokamak using the Divertor Material Evaluation System (DiMES). Two more RFEAs embedded in the lower divertor tiles are also to be deployed during the upcoming Tungsten Tile Testing (T3) Campaign. DiMES tests have demonstrated high quality signals in most of the scrape-off layer (SOL) with significant signal distortion under low temperature conditions (electron temperature, Te < 5 eV) such as the private flux region and suggest a Ti/Te ratio ranging from 1-4. The dependencies of Ti, including distance to separatrix, input power, and election density, are investigated and compared with Te from the Langmuir probes. Furthermore, particle-in-cell (PIC) simulations with realistic probe geometry and experimental conditions are utilized to decipher the signal distortions caused by space charge and selective transmission inside the RFEA cavity. The PIC-based workflow has shown effectiveness to significantly improve the interpretability of the signal and facilitates detailed analysis for ion energy distribution function (IEDF) at the divertor surface, beyond the conventional Maxwellian assumptions for the incident ions.