Observation of Electron-Temperature Fluctuations Triggered by Supersonic Gas Puffing in the LHD

Abstract

Non-local transport and electron temperature fluctuations triggered by supersonic gas puffing (SSGP) in high-temperature helical plasmas in the Large Helical Device (LHD) are reported. After a short-pulse SSGP, the core electron temperature increased while the edge electron temperature decreased. SSGP triggered a longer core temperature increase than that triggered by a small impurity pellet injection. The temperature profile, which was relatively flat inside the half minor radius before SSGP, became parabolic after non-local transport was triggered. Fluctuations were excited in the electron temperature signals around the half minor radius. The frequency of these fluctuations increased from ∼ 400 Hz to ∼ 1 kHz within ∼ 0.1 s and the amplitude decreased correspondingly. The temperature fluctuations inside and outside of the half minor radius had opposite phases. Magnetic fluctuations resonating near the half minor radius were observed simultaneously with the electron temperature fluctuations.