Behavior of CIII to CVI emissions during the recombining phase of LHD plasmas

Carbon emissions of CIII-CVI during the recombining phase of the Large Helical Device (LHD) plasma are studied to understand their behaviors. To achieve this, four resonance transitions of CIII (977A: 2 s21S-2s2p 1P), CIV (1548A: 2s 2S-2p 2P), CV (40.27A: 1s21S-1s2p 1P), and CVI (33.73A: 1s 2S-2p 2P) are observed using absolutely calibrated VUV monochromators and EUV spectrometers. A one-dimensional impurity transport code has been used to calculate spectral emissivity under the consideration of measured ne and Te profiles. The temporal evolution of line emissions has been calculated and compared with the measured data. The comparison shows that the carbon density is 3% of the electron density. However, a discrepancy between the calculated and measured values has been noticed in CIII and CIV emissions. It has been argued that three-dimensional structures of CIII and CIV emissions are likely to be the reason for this difference, which is based on the presence of relatively high-density and high-temperature plasmas in edge ergodic layer in LHD. It is also found that the CV and CVI emissions during the recombining phase increase with electron density, whereas these are nearly constant during steady state phase. This strongly suggests the disappearance of the edge particle screening effect in the recombining phase. (author)