Correlations between Impurity Ion Tangential Velocities and Electron Density Rotational Modes in the C-2W Experiment

The C-2W experiment is a Field-Reversed Configuration plasma device directed towards studies of beam-driven, magnetically confined fusion plasmas. As part of the upgrade from the preceding C-2U device, new magnetic systems, more powerful neutral beams, internal expansion chambers, and biasing electrodes were added to improve energy confinement times, particles temperatures, plasma stability and control. Many interesting dynamics arise from the rotational modes of the plasma, one of which being the so-called N=2 elliptical mode. This plasma deformation arises non-destructively during many high energy pulses, and is observed on a range of diagnostics. The ability of the new iChers spectrometer to measure temporally and spatially resolved impurity ion velocities and temperatures provides an interesting opportunity to observe the relationship between the plasma rotational velocity and some of its rotational modes. The spectrometer provides a velocity resolution of 4.0 km/s at short wavelengths, such as for 278.1 nm (O-V), and 1.5 km/s at longer wavelengths like 656.52 nm (Da).