Predicting high harmonic ion cyclotron heating efficiency in Tokamak plasmas

Area of Science:

• Plasma Physics
• Fusion Energy Research
• Radio Frequency Heating

Background:

• High-confinement (H-mode) plasmas in fusion devices like tokamaks are crucial for achieving efficient energy production.
• Radio frequency (RF) heating is a key technique for heating these plasmas to fusion-relevant temperatures.
• Observed variations in RF heating efficiency in experimental devices necessitate detailed investigation.

Purpose of the Study:

• To investigate the causes of improved and reduced RF heating efficiency in ITER-relevant H-mode plasmas.
• To correlate specific antenna launching conditions with observed heating performance.
• To identify the physical mechanisms responsible for RF heating efficiency variations.

Main Methods:

• Whole-device linear simulations were employed to model RF electric fields.
• Calculations were performed for various antenna spectra, focusing on toroidal wave numbers.
• The simulations examined the excitation of standing modes in the plasma edge and scrape-off layer.

Main Results:

• Launching specific toroidal wave numbers leads to fast-wave propagation in the scrape-off plasma.
• This propagation excites large-amplitude coaxial standing modes (∼kV/m).
• These modes form between the plasma density pedestal and the vessel wall.

Conclusions:

• Coaxial standing modes excited by RF waves are identified as a probable cause of degraded heating efficiency.
• The findings suggest that antenna spectrum control is critical for optimizing RF heating in tokamaks.
• Understanding these wave-plasma interactions is essential for future fusion reactor designs.