Overview of Diagnostics for Nonsolenoidal Initiation Stuides

Pegasus-III, an ultralow aspect ratio spherical tokamak (A~1.2, I_p<0.3 mA, B_T≤0.6 T, t~100 ms) with T_e~50 eV, n_e~10¹⁹ m^-3 plasmas to date, focuses on the physics of non-solenoidal plasma current drive and initiation while developing technologies to advance tokamak devices towards a fusion pilot plant. In support of the non-solenoidal research, Pegasus-III uses an expanding diagnostics suite. The standard diagnostic set includes: a magnetic suite for MHD mode analysis, an impurity diagnostic suite (SPRED and AXUV diode array) for injector performance studies with integrated modelling using Aurora, a multipoint Thomson scattering system for electron temperature and density measurements with a ~3 cm spatial resolution within 20 cm < R < 80 cm, a synthetic aperture microwave diagnostics for measuring EBW emission (18-30 GHz), and a stark broadening diagnostic for LHI arc density measurements. Aspects of the diagnostic suite under development are a compact NPA for line integrated ion temperature, a diagnostic neutral beam (80 kV, 4 A,100 ms) to measure current density fluctuations, filterscopes, magnetic probes, Langmuir probes, and Mach probes. Experimental measurements and projections of diagnostic improvement are presented.