Convergence Study of Long-Term ITG Turbulence Simulations with the GTC Code

The 3D gyrokinetic particle-in-cell code GTC has been successfully employed in studying microturbulence in toroidal fusion devices for several years now [1]. Recently, new GTC simulations of ITG turbulence using the adiabatic electron approximation but including the usually ignored ion velocity-space nonlinearity showed a faster evolution towards steady-state than the original simulations without this extra term [2]. In this work, several simulations of this type are carried out to assess the convergence of the steady-state transport for an increasing number of particles at a fixed device size. The resulting ion thermal conductivity, entropy production, and perturbed velocity-space distribution will be presented.\newline [1] Z. Lin, T. S. Hahm, S. Ethier, and W. M. Tang, \textit{Phys. Rev. Lett.} \textbf{88}, 195004 (2002). \newline [2] W. W. Lee, ``Steady State Global Simulations of Microturbulence,'' \textit{Bull. Am. Phys. Soc}. \textbf{49}, no. 8, 135 (2004).