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

The Pegasus-III experiment is an ultra-low A ST focused on solonoid free plasma initiation and sustainment techniques, including helicity injection and a planned 28 GHz microwave heating and CD system. To enable operation in overdense plasmas (ne > 1e19 m-3), a system capable of both Electron Bernstein Wave (EBW) and EC heating will be implemented. The synthetic aperture microwave imaging diagnostic (SAMI) is being used to carry out EBW emission measurements of local helicity injection (LHI) plasmas to assist in the development of this system. SAMI uses phased array interferometry to map microwave emission from the plasma edge. Measurements of microwave power emitted from LHI plasmas have been made. Analysis to understand how plasma conditions, including stream-dynamics, impact microwave emission is ongoing, as is exploration of plasma conditions that could allow imaging of an EBW mode conversion window on Pegasus-III. Emission modeling using the OXB mode conversion scheme has been conducted for typical BT~0.3 T and BT~0.6 T Pegasus-III plasmas with peak ne of 4e19 m-3 and Te of 40 eV. Absorption at the 5th (rho~0.4) and 2nd (rho~0.02) EC harmonics respectively were predicted, along with driven current ranges and effects of collisional damping.