Microwave Preionization System of the MEPhIST-0 Tokamak

Microwave preionization is a common technique used for electron-cyclotron resonance assisted plasma start-up in spherical tokamaks. The purpose of this work is to test the developed MEPhIST-0 tokamak preionization system and to study the preliminary preionization plasma. The gas discharge parameters are measured using Rogowski coils, optical spectroscopy, and Langmuir probes. A fast CCD camera is additionally used to capture the emission during the discharge. The results show that the preliminary plasma discharge is localized at a certain distance inside the vacuum chamber, which satisfies the condition for the existence of electron cyclotron resonance. The estimated plasma density and electron temperature are 5.5 × 10 16 m –3 and 8 eV, respectively.