Effect of Ellipticity on Thermal Transport in ECH Plasmas in LHD

抄録

Effect of ellipticity on thermal transport was investigated in ECH plasmas in LHD. Ellipticity κ is scanned from 0.8 to 1.4 by controlling the quadrupole magnetic field. Experimental data of energy confinement time align with the scaling for all configurations; however, there exist systematic offsets. Performance τ_E^exp /τ_E^ISS04 is summarized as 0.94 ± 0.02 for κ = 0.8, 1.41 ± 0.07 for κ = 1.0, and 0.91± 0.03 for κ = 1.4. Local transport analysis based on power balance indicates that the anomalous transport predominates the plasma transport. However, the observed anomaly shows correlation with the change in the effective helical ripple ε_eff. Physical background of this correlation and the dependence on the poloidal viscous damping rate C_p is discussed. The present experimental comparison suggests a negative evidence for the relevance of C_p.