Computational Study of the Supersonic Molecular Beam Injection in Thailand Tokamak-1 based on the 2D Fluid Model

The successful operation of a tokamak requires effective and appropriate methods of plasma fueling. In the development plan for Thailand Tokamak-1 (TT-1), the use of supersonic molecular beam injection (SMBI) has been proposed as a method that can more effectively and deeply deliver fueling gas compared to the gas puffing method. In this study, we used 2D fluid simulation to investigate the impact of SMBI on plasma transport in TT-1. Our model incorporated the continuity equations, energy balance equations, momentum equation, continuity of fuel equations, and momentum equation of fuel. BOUT++ is then used to solve these equations by a finite difference method with the field-aligned coordinates in the edge region of the tokamak. Our simulation results showed that when hydrogen fuel gas is injected into the plasma via SMBI from the low-field side at the speed in the range of 600 - 1200 m/s, the electron density in the edge region locally increases due to dissociation and ionization in the region where the fuel gas meets the plasma. This subsequently leads to a decrease in the ion and electron temperatures. The increased density then spreads throughout the plasma volume within approximately 10 ms. Increasing the injection speed leads to a deeper penetration length for the fuel deposition. © 2024 The Japan Society of Plasma Science and Nuclear Fusion Research. All Rights Reserved.