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The paper presents a review of dynamic stabilization mechanisms for plasma instabilities. One of the dynamic stabilization mechanisms for plasma instability was proposed in the papers [Phys. Plasmas 19, 024503(2012) and references therein], based on a perturbation phase control. In general, instabilities emerge from the perturbations of the physical quantity. Normally the perturbation phase is unknown so that the instability growth rate is discussed. However, if the perturbation phase is known, the instability growth can be controlled by a superimposition of perturbations imposed actively: if the perturbation is introduced by, for example, a driving beam axis oscillation or so, the perturbation phase can be controlled and the instability growth is mitigated by the superimposition of the growing perturbations. Based on this mechanism we present the application results of the dynamic stabilization mechanism to the Rayleigh-Taylor (R-T) instability and to the filamentation instability as typical examples in this paper. On the other hand, in the paper [Comments Plasma Phys. Controlled Fusion 3, 1(1977)] another mechanism was proposed to stabilize the R-T instability based on the strong oscillation of acceleration, which was realized by the laser intensity modulation in laser inertial fusion [Phys. Rev. Lett. 71, 3131(1993)]. In the latter mechanism, the total acceleration strongly oscillates, so that the additional oscillating force is added to create a new stable window in the system. Originally the latter mechanism was proposed by P. L. Kapitza, and it was applied to the stabilization of an inverted pendulum. In this paper we review the two dynamic stabilization mechanisms, and present the application results of the former dynamic stabilization mechanism.
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The previous study regarding the stabilization of a magnetized constant temperature plasma by shear flow with vorticity is extended to a plasma of non-constant temperature, where in the presence of heat source or sinks the thermomagnetic Nernst effect becomes important. Of special interest is what this effect has on the stabilization of a linear z-pinch discharge for which exact solutions are given. Solutions which are unstable for subsonic shear flow become stable if the flow is supersonic.
The two-fluid (ions and electrons) plasma Richtmyer-Meshkov instability of a cylindrical light/heavy density interface is numerically investigated without an initial magnetic field. Varying the Debye length scale, we examine the effects of the coupling between the electron and ion fluids. When the coupling becomes strong, the electrons are restricted to co-move with the ions and the resulting evolution is similar to the hydrodynamic neutral fluid case. The charge separation that occurs between the electrons and ions results in self-generated electromagnetic fields. We show that the Biermann battery effect dominates the generation of magnetic field when the coupling between the electrons and ions is weak. In addition to the Rayleigh-Tayler stabilization effect during flow deceleration, the interfaces are accelerated by the induced spatio-temporally varying Lorentz force. As a consequence, the perturbations develop into the Rayleigh-Taylor instability, leading to an enhancement of the perturbation amplitude compared with the hydrodynamic case.
Exact solutions of a magnetized plasma in a vorticity containing shear flow for constant temperature are presented. This is followed by the modification of these solutions by thermomagnetic currents in the presence of temperature gradients. It is shown that solutions which are unstable for a subsonic flow, are stable if the flow is supersonic. The results are applied to the problem of vorticity shear flow stabilization of a linear z-pinch discharge.
A dynamic mitigation mechanism of the two-stream instability is discussed based on a phase control for plasma and fluid instabilities. The basic idea for the dynamic mitigation mechanism by the phase control was proposed in the paper [Phys. Plasmas 19, 024503(2012)]. The mitigation method is applied to the two-stream instability in this paper. In general, instabilities appear from the perturbations, and normally the perturbation phase is unknown. Therefore, the instability growth rate is discussed in fluids and plasmas. However, if the perturbation phase is known, the instability growth can be controlled by a superimposition of perturbations imposed actively. For instance, a perturbed driver induces a perturbation to fluids or plasmas; if the perturbation induced by the perturbed driver is oscillated actively by the driver oscillation, the perturbation phase is known and the perturbation amplitude can be controlled, like a feedforward control. The application result shown in this paper demonstrates that the dynamic mitigation mechanism works well to smooth the non-uniformities and mitigate the instabilities in plasmas.
A dynamic mitigation mechanism for instability growth was proposed and discussed in the paper [Phys. Plasmas 19, 024503 (2012)]. In the present paper the robustness of the dynamic instability mitigation mechanism is discussed further. The results presented here show that the mechanism of the dynamic instability mitigation is rather robust against changes in the phase, the amplitude and the wavelength of the wobbling perturbation applied. Generally instability would emerge from the perturbation of the physical quantity. Normally the perturbation phase is unknown so that the instability growth rate is discussed. However, if the perturbation phase is known, the instability growth can be controlled by a superposition of perturbations imposed actively: if the perturbation is induced by, for example, a driving beam axis oscillation or wobbling, the perturbation phase could be controlled and the instability growth is mitigated by the superposition of the growing perturbations.
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