Investigating The Role of Impurities in Plasma Startup Via LHI on Pegasus-III

The influence of impurities in plasma start-up is investigated for local helicity injection on Pegasus-III. Impurity studies are critical to understanding helicity dissipation during the initial ramp-up and the power balance after the handoff. Previous Pegasus experiments at low B_T show that transport plays an important role in the charge-state balance of impurity distribution and radiative power losses. The new Pegasus-III facility will operate up to B_T of 0.6 T enabling a wider range of transport levels as confinement in LHI is predicted to improve with B_T. In preparation for these experiments, the impurity diagnostics have been upgraded. A high-resolution grating was installed on SPRED to help identify previously unresolved lines. New coupling optics on a visible spectrometer allow the use of the whole CCD to improve the measurement of bremsstrahlung to determine Z_eff. A new 32-channel AXUV radiometer was designed and calibrated for P_rad measurements. This set of diagnostics will be used in conjunction with STRAHL to assess the impurity dynamics. The information obtained from these experiments is used to extrapolate the performance of LHI in larger scale devices and potentially future fusion power plants.