Using the spontaneous transition condition under marginal hot cathode biasing, the ion viscosity at the L–H transition was estimated in various magnetic configurations in the Tohoku University Heliac. The critical viscosity, which is the viscosity at the transition point, was experimentally estimated from the J × B driving force. The critical viscosities in different magnetic configurations were in agreement with the neoclassical predictions within a factor of 2 and were compared with the viscosities obtained in the externally forced biasing experiments. Although the transition points were spread over a wide range, poloidal Mach numbers at the transition point were concentrated near the viscosity maxima predicted by the theory.
限界ホットカソードバイアス下での自発遷移条件を用いて、東北大学ヘリアック装置の様々な磁場配位においてL-H遷移時のイオン粘性を評価した。遷移点における粘性である臨界粘性は、J×B駆動力を用いて実験的に見積もられた。異なる磁場配位における臨界粘性は、新古典理論予測と2倍以内の誤差で一致し、外部強制バイアス実験から得られた粘性と比較された。遷移点は広い範囲に分布していたが、遷移時のポロイダルマッハ数は理論が予測する粘性極大値付近に集中していた。