Description
The Compact Toroidal Injection (CTI) system, known for its extremely high energy injection density, is considered a key technology for core fueling in future fusion reactors. A series of CTI plasma injection experiments have been conducted on the EAST superconducting tokamak, revealing not only significant core fueling phenomena but also notable effects on high-frequency magnetohydrodynamic (MHD) instabilities in the main plasma. Following the CTI injection, a dramatic reduction in background turbulence was observed, alongside the excitation of a high-frequency mode with a poloidal mode number of -2. This mode frequency initially rose rapidly from 130 kHz to 200 kHz before decaying back down. Statistical analysis revealed a correlation between mode excitation and the presence of background fast electrons, suggesting an interaction mechanism between the fast particles and the instability. Additionally, the mode showed a clear density threshold, being excited only at lower plasma densities. A further investigation into the frequency behavior showed that it is inversely proportional to the local plasma density in the region of CTI injection, with the mode frequency also displaying a linear relationship with the calibrated frequency of the toroidal Alfvén eigenmode (TAE). During the excitation of this mode, high-frequency magnetic probes detected the emergence of edge tearing modes, which might be attributed to the magnetic field structure embedded within the CTI plasma. This structure could trigger small-scale magnetic reconnection events, generating high-energy particles that subsequently excite TAE-like instabilities. This research provides valuable insights into the fueling dynamics of CTI, shedding light on how the CTI plasma injection affects both the background plasma and its MHD behavior. The findings have significant implications for understanding the interaction between injected fueling plasmas and the core plasma, as well as for the design and optimization of fueling systems in future tokamaks.