  We present a convergence study of the gyromoment (GM) approach, which is
based on projecting the gyrokinetic distribution function onto a
Hermite-Laguerre polynomial basis, focused on the cyclone base case (CBC) (Lin
et al. 1999) and Dimits shift (Dimits et al. 2000) as benchmarks. We report
that the GM approach converges more rapidly in capturing the nonlinear dynamics
of the CBC than the continuum GENE code (Jenko et al. 2000) when comparing the
number of points representing the velocity space. Increasing the velocity
dissipation improves the convergence properties of the GM approach, albeit
yielding a slightly larger saturated heat flux. By varying the temperature
equilibrium gradient, we show that GM approach successfully reproduces the
Dimits shift (Dimits et al. 2000) and effectively captures its width, which is
in contrast to the gyrofluid framework. In the collisional regime, the
convergence properties of the GM approach improve and a good agreement with
previous global PIC results on transport is obtained (Lin et al. 1999).
Finally, we report that the choice of collision model has a minimal impact both
on the ITG growth rate and on the nonlinear saturated heat flux, at
tokamak-relevant collisionality.
