The hot-electron closure of the moment-based gyrokinetic plasma model

We derive the hot-electron-limit (HEL) closure for the moment hierarchy used to solve the gyrokinetic equations, known as the gyromoment (GM) approach. By expanding the gyroaveraging kernels in the small ion-to-electron temperature ratio limit, $\tau \ll 1$ , and retaining only the essential $\mathcal{O}(\tau )$ terms, we obtain a closed system for the density, parallel velocity and parallel and perpendicular temperatures. In a Z-pinch geometry, the GM system with the HEL closure is analytically equivalent to the one developed by Ivanov et al. (2022 J. Plasma Phys. , vol. 88, no. 5, p. 905880506). Numerical benchmarks confirm the closure’s accuracy, reproducing established linear growth rates, nonlinear heat transport and low collisionality dynamics. An extension to the tokamak-relevant $s{-}\alpha$ geometry and a comparison with gyrokinetic simulations reveal the capabilities and limitations of the HEL-closed GM model: while transport levels and the temporal dynamics are qualitatively preserved even at $\tau =1$ , the absence of higher-order kinetic moments prevents an accurate prediction of the Dimits shift and of transport suppression.