Solenoid-Free Plasma Initiation Research on the Pegasus-III Experiment

Pegasus-III (A ~ 1.2, I_p ≤ 0.3 MA, B_T ≤ 0.6 T) is a spherical tokamak investigating solenoid-free plasma initiation. Recent work has been on expanding diagnostic capabilities and exploring new injector technologies. Pegasus-III increased the spatial resolution of its SPRED system to resolve metallic lines in the 10-32 nm range, improved the multi-point Thomson scattering system to obtain profiles from a single laser pulse, and deployed a compensation loop to help capture the diamagnetic flux. A 28 GHz gyrotron was acquired for microwave heating, and EBE measurements have continued with the SAMI diagnostic. Several machine learning models are in development, including a cathode spot detection system that has completed initial testing. To maximize the plasma current limit from Taylor relaxation, a non-circular injector was installed and tested, achieving I_p ≤ 0.1 MA with I_inj ≤ 4 kA, V_inj ≤ 700V. Construction has started on a test facility to condition injector components and rapidly prototype injector technology. Near term work will focus on deployment of a novel coaxial helicity injection system, initial testing of the injector testbed, continued helicity injection studies at B_T ~ 0.6 T, and design of a 28 GHz microwave heating.