EBW Emission Measurements for Development of a Microwave System on Pegasus-III*

The Pegasus-III experiment is an ultra-low A solenoid-free ST focused on non-solenoidal plasma startup and sustainment techniques with helicity injection and a microwave heating and CD system. To enable operation in overdense plasmas, a 28 GHz system capable of both Electron Bernstein Wave (EBW) and EC heating will be implemented. The synthetic aperture microwave imaging diagnostic (SAMI) will be used to carry out the first exploration of EBW emission measurements, via OXB mode conversion, in helicity injection plasmas to assist in the development of this system. SAMI uses phased array interferometry to locate microwave sources in the plasma edge, such as the EBW mode conversion window. Calibrations of the diagnostic hardware are nearing completion and full experimental measurements of the EBW mode conversion windows in Pegasus-III are expected to begin summer 2024. The microwave system will allow direct tests of synergistic improvements to HI startup and ramp-up scenarios by microwave injection.