Full-orbit NBI injection studies for the SMART tokamak

The full orbit-following SPIRAL code [1] was used to investigate NBI injection, loss, and deposition in the SMall Aspect Ratio Tokamak (SMART) [2] for a positive (PT) and negative (NT) triangularity plasma shape. SMART is designed to study plasma shape effects in a spherical tokamak (ST) with a major radius of 0.4 m, minor radius of 0.2 m, triangularity |δ|<0.5, and elongation κ<2.25,maximum toroidal magnetic field of 2~T, and plasma current 1.0~MA. In the present study a toroidal magnetic field of 0.4~T and a current of 0.2~MA were used. A 25 kV NBI hydrogen system, nominal power 225 kW, tangency radius of 0.44 m, is being installed and injects in the co-current direction. Due to the high NBI energy and low magnetic fields, the gyro radii of the NBI ions are large, up to 20% of the minor radius. Therefore, the NBI dynamics can only be studied meaningfully using full-orbit simulations. Several NBI loss mechanisms: shine-through, prompt, scattering, and charge exchange are studied with the loss boundary at the vessel wall. The effects of confined NBI ions on the the plasma are also presented in the form of 2D heating, fueling, and current profiles. It is concluded that the NBI system is well suited for positive and negative triangularity plasma shapes.

[1] G.J. Kramer et al. PPCF 55 (2013) 025013

[2] A. Mancini, et al. FED 192 (2023) 113833