# The collisional drift wave instability in steep density gradient regimes

## TL;DR

This paper investigates the collisional drift wave instability in steep density gradient regimes using a full-F gyro-fluid model, revealing significant corrections to previous approximations and identifying non-modal phenomena and localized turbulence.

## Contribution

It introduces a full-F gyro-fluid model that relaxes the OB approximation, providing new insights into drift wave behavior in steep density gradients.

## Key findings

- Corrections of order one to eigenvalues compared to OB approximations
- Discovery of non-modal phenomena and localized growth patterns
- Persistence of non-modal effects in nonlinear turbulence

## Abstract

The collisional drift wave instability in a straight magnetic field configuration is studied within a full-F gyro-fluid model, which relaxes the Oberbeck-Boussinesq (OB) approximation. Accordingly, we focus our study on steep background density gradients. In this regime we report on corrections by factors of order one to the eigenvalue analysis of former OB approximated approaches as well as on spatially localised eigenfunctions, that contrast strongly with their OB approximated equivalent. Remarkably, non-modal phenomena arise for large density inhomogeneities and for all collisionalities. As a result, we find initial decay and non-modal growth of the free energy and radially localised and sheared growth patterns. The latter non-modal effect sustains even in the nonlinear regime in the form of radially localised turbulence or zonal flow amplitudes.