Accuracy of higher-order gyrofluid pressure nonlinearities

Determine whether retaining additional nonlinear terms in a properly formulated gyrofluid representation of finite-Larmor-radius physics improves the small-scale behavior of ion-temperature-gradient models and accurately captures pressure nonlinearities.

Background

The paper argues that the diamagnetic nonlinearity used in the fluid models is a low-wavenumber Taylor expansion of more complete gyrofluid finite-Larmor-radius physics. At small scales, this truncated representation produces pathological behavior and forces the simulations to use unusually strong hyperviscosity.

The authors suggest that retaining further terms or using a direct gyrofluid finite-Larmor-radius representation might improve the model, but they leave unresolved whether such modifications actually reduce the small-scale error and whether pressure nonlinearities can be included accurately.

References

Instead, using a gyrofluid model with a proper FLR representation directly may allow us to capture $k\gg1$ behavior of ITG more accurately. However, including pressure nonlinearities in such models is not trivial and involves additional assumptions, whose accuracy needs to be tested in the current context, which we leave for future studies.

— The role of different nonlinearities and potential vorticity conservation in two-dimensional fluid ITG models  (2609.01414 - Paramasivam et al., 1 Sep 2026) in Section 6, Conclusion