Garden-hose instability in high-beta plasmas

This paper reviews the theory of classical garden-hose instability in high-beta plasmas. The garden-hose (or fire-hose) instability is a hydromagnetic instability that is due to the nonresonant wave-particle interaction. Therefore, to the lowest order, it is customary to describe the instability under the assumption of hydromagnetic perturbation. The hydromagnetic assumption implies that the characteristic wave frequency (or the growth rate) is much lower than the ion gyrofrequency, and that the ion gyroradius is sufficiently smaller than the characteristic wavelength associated with the perturbation. As a result, the ion gyroradius is often taken to be zero at the outset. However, it was recently discovered that keeping the ion gyroradius finite (however small it may be) results in a fundamental alteration of the basic property of the instability. The article also reviews the nonlinear theory of the garden-hose instability.