Quasi-Optical Simulations of Scenarios with the Second Harmonic Electron Cyclotron Plasma Heating at the GDT Facility

The absorption of microwave radiation in the GDT open magnetic trap (Budker Institute of Nuclear Physics) was studied using a new scheme of electron cyclotron resonance plasma heating at the second harmonic, in which radiation in the form of the extraordinary wave was launched almost transverse to the plasma column. When performing numerical simulations, the full-aberration quasi-optical approach was used, which was verified using the first experimental data, obtained at the facility. The optimal scenarios using the new heating system were analyzed. It was found that in the current configuration, the total efficiency of microwave heating does not exceed 60%, which is considerably less than that planned when designing the system. This occurs due to the tangential reflection of heating radiation from the resonance region; this is a wave effect that was previously not taken into account within the framework of the geometric-optics approximation. It was shown that heating at the second harmonic does not result in excitation of the “overheating” instability of the electron component observed during heating at the first harmonic; on the whole, the wide power deposition profile is formed in this case. This is an advantage of the new scheme, since it makes it possible to avoid the development of MHD plasma instabilities associated with peaked power release at the axis of the plasma column.