Turbulence Transition in Magnetically Confined Hydrogen and Deuterium Plasmas
T. Kinoshita, K. Tanaka, A. Ishizawa, H. Sakai, M. Nunami, Y. Ohtani, H. Yamada, Masahiko Sato, M. Nakata, T. Tokuzawa, Ryo Yasuhara, Y. Takemura, I. Yamada, H. Funaba, K. Ida, M. Yoshinuma, T. Tsujimura, R. Seki, K. Ichiguchi, C. Michael
Abstract
In this study, we discovered a turbulence transition in a large helical device. The turbulence level and turbulence-driven energy transport decrease to a specific transition density and increase above it. The ruling turbulences below and above the transition density were ion-temperature gradient (ITG) and resistive-interchange (RI) turbulences, consistent with the predictions of gyrokinetic theory and two-fluid MHD model, respectively. Isotope experiments on hydrogen (H) and deuterium (D) clarified the role of transitions. In the ITG regime, turbulence levels and energy transport were comparable in the H and D plasmas. In contrast, in the RI regime, they were clearly suppressed in the D plasma. The results provide crucial knowledge for understanding isotope effects and future optimization of stellarator and heliotron devices.