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.
Highlights
In a series of seminal theoretical works in the early 1960s it has been established that low-frequency small scale instabilites are naturally immanent to magnetically confined plasmas [1,2,3,4,5,6]
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
We focus our study on steep background density gradients
Summary
In a series of seminal theoretical works in the early 1960s it has been established that low-frequency small scale instabilites are naturally immanent to magnetically confined plasmas [1,2,3,4,5,6]. The latest efforts focus on a unified description of the collisional and collisionless DW instability [28, 29] or proof instability for collisionless DWs in sheared magnetic fields after decades of misconception [19] Another outstanding regime of interest is that of large inhomogeneities, in particular if the background density varies over more than one order of magnitude. In this contribution we investigate the linear dynamics of the collisional DW instability for steep background density gradients This is achieved by consistently linearising a nonOberbeck–Boussinesq (NOB) approximated full-F gyro-fluid model [39], which accurately accounts for collisional friction between electrons and ions along the magnetic field.
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