Electromagnetic gyrokinetic simulation of drift wave turbulence in ADITYA-U with collisions

Abstract In this work, we extend our previous studies Singh et al (2023 Nucl. Fusion 63 086029, Singh et al (2024 Nucl. Fusion 64 106005) by performing global δ f electromagnetic gyrokinetic simulations including collisions using the ORB5 particle-in-cell code, spanning the plasma from magnetic axis to separatrix. The analysis focuses on ion temperature gradient (ITG) and trapped electron mode (TEM) turbulence in both linear and nonlinear regimes for experimentally relevant profiles and parameters of the ADITYA-U tokamak, employing realistic MHD equilibria with circular ( κ = 1.0 ) and elongated ( κ = 1.2 , 1.4 ) magnetic geometries. Linear simulations show that finite- β effects ( β = β e + β i = 1.0 × 10 − 3 ) reduce the ITG growth rates by approximately 10%. Owing to the relatively high collisionality of ADITYA-U plasmas, resulting from low electron temperatures, TEMs are strongly suppressed, leaving ITG and short-wavelength ITG modes as the dominant instabilities. Nonlinear simulations are performed for three cases: (i) electrostatic without collisions, (ii) electromagnetic without collisions, and (iii) electromagnetic with collisions. The results demonstrate that different physical mechanisms contribute distinctly to the reduction of turbulent transport. Magnetic shaping alone ( κ = 1.4 ) is found to reduce the ion heat flux by approximately 25% compared to the circular equilibrium. Electromagnetic effects further reduce the transport by about 10% relative to the electrostatic case. In addition, collisions lead to a further reduction of 25%–30%, primarily through the suppression of TEM turbulence and modification of turbulence saturation dynamics. These reductions are obtained from separate comparisons between simulations including or excluding the corresponding physical effects. In particular, collisions modify the electron response and suppress the trapped-electron contribution, leading to changes in both turbulence amplitude and saturation dynamics. Overall, the combined effect of magnetic shaping, finite- β , and collisions leads to a substantial reduction in turbulent transport in ADITYA-U, with ITG-dominated turbulence governing the transport in the high-collisionality regime.