Active spectroscopy measurements of the deuterium temperature, rotation, and density from the core to scrape off layer on the DIII-D tokamak (invited).

Abstract

Main-ion charge exchange recombination spectroscopy (MICER) uses the neutral beam induced D α spectrum to measure the local deuterium ion (D+) temperature, rotation, and density, as well as parameters related to the neutral beams, fast ions, and magnetic field. An edge MICER system consisting of 16 densely packed chords was recently installed on DIII-D, extending the MICER technique from the core to the pedestal and steep gradient region of H-mode plasmas where the D+ and commonly measured impurity ion properties can differ significantly. A combination of iterative collisional radiative modeling techniques and greatly accelerated spectral fitting allowed the extension of this diagnostic technique to the plasma edge where the steep gradients introduce significant diagnostic challenges. The importance of including the fast ion D α emission in the fit to the spectrum for the edge system is investigated showing that it is typically not important except for cases which can have significant fast ion fractions near the plasma edge such as QH-mode. Example profiles from an Ohmic L-mode and a high power ITER baseline case show large differences in the toroidal rotation of the two species near the separatrix including a strong co-current D+ edge rotation. The measurements and analysis demonstrate the state of the art in active spectroscopy and integrated modeling for diagnosing fusion plasmas and the importance of direct main ion measurements.