RECENT PROGRESS ON THE FAST ION STUDY IN THAILAND TOKAMAK-1

Thailand Tokamak-1 (TT-1) is a tokamak designed to confine hydrogen plasma with a plasma current of 100 kA and a magnetic field of 1.0 T. While the device currently relies on Ohmic heating, neutral beam injection shows promise as an auxiliary heating method. These additional heat sources can also generate fast ions that excite various MHD instabilities, for example, induced Alfvén eigenmodes (TAE), energetic-particle continuum modes (EPM), and energetic particle-driven geodesic acoustic modes (EGAM). These instabilities can lead to significant particle loss, reducing fusion yield and damaging the first wall. Thus, it is critical to comprehend the behavior and impact of fast ions for the successful future plasma operation of TT-1.

In this study, simulations of neutral beam injection (NBI) were performed using the Monte Carlo codes NUBEAM and HFREYA to assess NBI utilization. The study investigated various injection conditions, including beam energy and direction. Results indicate that a 20 keV beam launched in the co-current direction with a tangential radius of 0.55–0.65 m is suitable for TT-1. Incorporating the toroidal field ripple, the simulations show that most beam ions escape the last closed flux surface (LCFS) in the region between toroidal field coils due to banana drift loss and the grad-B drift effect. Furthermore, Alfvén eigenmodes were computed in fully three-dimensional equilibria of shear Alfvén waves using the AE3D code. The analysis reveals that the gap frequencies occur within the range of 130–300 kHz. The minimum beam energy required to excite the TAE modes is 2 keV at the sideband resonance condition.