Universal instability for wavelengths below the ion Larmor scale

Abstract

We demonstrate that the universal mode driven by the density gradient in a plasma slab can be absolutely unstable even in the presence of reasonable magnetic shear. Previous studies from the 1970s that reached the opposite conclusion used an eigenmode equation limited to $L_x\gg {\rho }_i$, where $L_x$ is the scale length of the mode in the radial direction, and ${\rho }_i$ is the ion Larmor radius. Here we instead use a gyrokinetic approach which does not have this same limitation. Instability is found for perpendicular wavenumbers $k_y$ in the range $0.7\lesssim k_y{\rho }_i\lesssim 100$, and for sufficiently weak magnetic shear: $L_s/L_n\ge 17$, where $L_s$ and $L_n$ are the scale lengths of magnetic shear and density. Thus, the plasma drift wave in a sheared magnetic field may be unstable even with no temperature gradients, no trapped particles, and no magnetic curvature.

References in corpus (2)

• Linearized model Fokker-Planck collision operators for gyrokinetic simulations. I. Theory
• Multiscale Gyrokinetics for Rotating Tokamak Plasmas: Fluctuations, Transport and Energy Flows

Cited by in corpus (12)

• Generalized universal instability: Transient linear amplification and subcritical turbulence
• The universal instability in general geometry
• Theory of the Drift-Wave Instability at Arbitrary Collisionality
• Spontaneous and explicit parity-time-symmetry breaking in drift wave instabilities
• Gyrokinetic theory of slab universal modes and the non-existence of the Gradient Drift Coupling (GDC) instability
• Random and quasi-coherent aspects in particle motion and their effects on transport and turbulence evolution
• The collisional drift wave instability in steep density gradient regimes
• Finite $\beta$ Effects on Short Wavelength Ion Temperature Gradient Modes
• Microstability of $\beta \sim 1$ tokamak equilibria
• Influence of collisions on trapped-electron modes in tokamaks and low-shear stellarators
• Generalized slab universal instability and its appearance in pair plasma
• Influence of finite ion Larmor radius on the dynamics of weakly-collisional plasma jets colliding in magnetic arch