Electron temperature fluctuations in DIII-D divertor

For the first time electron temperature (T_e) fluctuations have been measured using a novel probe-based T_e fluctuation diagnostic with a bandwidth of 100 kHz in different regions of a tokamak divertor, revealing comparable levels and spectral characteristics to T_e fluctuations in the outboard scrape-off layer (SOL) under low density attached L-mode conditions. In most cases the relative T_e fluctuation levels in the divertor were between 0.2 – 0.6, comparable to those in the outboard midplane SOL. T_e fluctuation spectra had measurable energy up to the bandwidth of the diagnostics (100 kHz) and were rather similar in both regions at low density, while frequency roll-off was faster in the outboard midplane SOL at higher density. In the private flux near the divertor leg the maximum of T_e fluctuation energy is shifted towards lower energies compared to the adjacent SOL. The data suggests that turbulence originating upstream propagates to the divertor SOL under attached conditions. This new diagnostic provides a critical tool for validation of turbulence theory and codes in a diverted plasma configuration.