A study on the TAE-induced fast-ion loss process in LHD

作者：Ogawa K^*; Isobe M; Toi K; Shimizu A; Spong D A; Osakabe M; Yamamoto S

来源：Nuclear Fusion, 2013, 53(5): 053012.

DOI：10.1088/0029-5515/53/5/053012

Characteristics of fast-ion losses induced by toroidal-Alfven eigenmodes (TAEs) are investigated over wide parameter ranges of Large Helical Device (LHD) plasmas to reveal the fast-ion loss process. To study fast-ion losses, a scintillator-based lost-fast ion probe is used, and an increment of fast-ion loss flux due to TAEs from the neoclassical orbit loss level (Delta Gamma(fast ion)) is measured. The dependence of Delta Gamma(fast ion) on the TAE magnetic fluctuation amplitude (b(theta TAE)) changes from a linear to a quadratic and finally a third power with an increase in the magnetic axis shift. It is found that the dependence of fast-ion loss flux on TAE magnetic fluctuation amplitudes changes at a certain fluctuation level in a fixed configuration. Experimental results show that in the small b(theta TAE) regime, Delta Gamma(fast ion) is proportional to b(theta TAE), whereas Delta Gamma(fast ion) increases with the square of b(theta TAE) in the larger b(theta TAE) regime. A simulation by orbit-following codes that incorporate magnetic fluctuations with frequency chirping-down due to TAEs suggests the change in the fast-ion loss process from a convective (Delta Gamma(fast ion) proportional to b(theta TAE)) to a diffusive (Delta Gamma(fast ion) proportional to b(theta TAE)(2)) character as b(theta TAE) increases.

• 出版日期2013-5