EBW Emission Measurements for Development of a Microwave Heating System on the Pegasus-III Experiment

Development of non-solenoidal heating and current drive (CD) techniques are advantageous to advanced tokamak concepts and critical for spherical tokamaks (ST). Pegasus-III is an ultra-low A solenoid free ST focused on non-solenoidal plasma startup and sustainment techniques with local helicity injection (HI), coaxial helicity injection and RF. To enable heating and CD in overdense plasmas, Pegasus-III will implement a 28 GHz RF system capable of both electron Bernstein wave (EBW) and EC heating. For the development of this system, a synthetic aperture microwave imaging diagnostic (SAMI) [Thomas, D., Brunner, K., Freethy, S., Huang, B., Shevchenko, V., Vann, R., Nuclear Fusion 56 026013 (2016)] will be used to carry out the first exploration of EBW emission measurements from HI generated plasmas. The calibration and installation of SAMI on Pegasus-III began in early 2023. The RF system on Pegasus-III will allow direct tests and investigation into synergistic improvement of proposed startup and ramp-up scenarios, providing results relevant for larger scale ST and reactor technologies.