Observations of cold, high density plasma in the private flux region of the Alcator C-Mod divertor

Abstract Significant plasma density has been observed in the private flux zone of the Alcator C-Mod tokamak. The behavior of the Dγ emission profiles is consistent with the source of the plasma being due to an E → × B → drift generated by a poloidal temperature gradient. The plasma flux due to this drift is derived and evaluated. A plasma flux into the private flux zone is inferred by measurements of volumetric recombination using a tangentially viewing CCD camera and several spectroscopic views observing the high n-lines of the D0 Balmer series. For the case of an attached divertor the inferred plasma flux to the PFZ has a linear scaling with respect to plasma pressure, as is expected from the temperature-gradient-induced, E → × B → drift.