LH transition by a biased hot cathode in the Tohoku University Heliac

S. Kitajima, H. Takahashi, Y. Tanaka, H. Utoh, M. Sasao, M. Takayama, K. Nishimura, S. Inagaki, M. Yokoyama

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21 Citations (Scopus)


In the Tohoku University Heliac (TU-Heliac), a helical axis stellarator, an electron injection electrode using a hot cathode made of LaB6 was developed and the transition mechanism to an improved mode has been intensively studied. In the electrode current-sweep mode of biasing experiments, a bifurcation phenomenon, i.e. a negative resistance feature in the electrode characteristics was observed accompanied with transition to an improved mode (H-mode) or transition from H-mode to L-mode, in helium plasma discharges of a wide range of collisionality. The ion viscous damping force was estimated from the J × B driving force for poloidal rotation. The local maxima in viscosity were found at the poloidal Mach number around -Mp ∼ 1-3, as predicted by neoclassical theory. It was also found that the negative resistance (a bifurcation phenomenon) was observed when the poloidal viscosity showed a local maximum.

Original languageEnglish
Pages (from-to)200-206
Number of pages7
JournalNuclear Fusion
Issue number2
Publication statusPublished - Feb 1 2006
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Nuclear and High Energy Physics
  • Condensed Matter Physics

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    Kitajima, S., Takahashi, H., Tanaka, Y., Utoh, H., Sasao, M., Takayama, M., Nishimura, K., Inagaki, S., & Yokoyama, M. (2006). LH transition by a biased hot cathode in the Tohoku University Heliac. Nuclear Fusion, 46(2), 200-206. https://doi.org/10.1088/0029-5515/46/2/002