Observation of detachment in the JET MkIIGB divertor using CCD camera tomography

In this paper, we discuss Dα and Dγ profiles in a density limit discharge in L-mode. CCD camera tomography was developed, calibrated with KS3 visible spectroscopy and utilized to observe two-dimensional change in Dα and Dγ profiles. A significant difference in Dα profiles was found between the inner and outer divertor. While the Dα profile extended to fill the inner divertor as the plasma density increased, in the outer divertor the Dα profile extended along the separatrix. From the comparison of Dα and Dγ profiles along the separatrix, it was found that recombination became significant and the recycling peak shifted upstream before full detachment of both the inner and outer divertor.