Development of an ECH Heating Efficiency Database for KSTAR H-Mode Plasmas

Electron cyclotron heating (ECH) plays an important role in plasma startup, heating, and current drive. However, several KSTAR experiments suggest that the heating efficiency of ECH in H-mode plasmas is expected to be lower than that of neutral beam injection (NBI). To investigate this, we used GENRAY ray-tracing simulations and electron cyclotron emission (ECE). The 1D radial power absorption profile from GENRAY is well matched with the initial increase of measured electron temperature within the first few milliseconds, indicating that initial energy deposition is effective for the discharge. However, we still investigate the possibility that the wave polarization from the gyrotron is not well aligned with the plasma magnetic field, which reduces the power absorption of ECH in other conditions. Even if the initial RF power absorption is sufficiently good, the heating efficiency that is defined as the increase of the stored energy in the long transport time can be attributed to plasma transport changes, such as increased thermal diffusivity due to turbulence or density pumpout. Based on these results, we are developing a database of ECH heating efficiency for different KSTAR discharges to better understand the relationship between plasma transport and ECH performance.

This research was supported by R&D Program of “High Performance Tokamak Plasma Research & Development (EN2501)” through the Korea institute of Fusion Energy(KFE) funded by the Government funds, Republic of Korea