Instability In Magnetized Plasma Research Articles

Effects of Controlled Flow-Shear on Low-Frequency Instabilities in Magnetized Plasmas

The external and independent control of parallel and perpendicular flow shears in collisionless magnetized plasmas are realized using two newly-developed plasma sources. The ion flow velocity shears parallel to the magnetic-field lines are then observed to destabilize not only the D’Angelo mode but also the drift-wave instability depending on the sign of the parallel shear in the absence of field-aligned electron drift flow in laboratory experiments. On the other hand, perpendicular ion flow velocity shears are demonstrated to suppress the drift-wave and the ion-cyclotron instabilities, and furthermore, these suppressions are found to take place independently of the sign of the perpendicular shear.

Effects of Controlled Flow Velocity Shear in Open-Ended Magnetized Plasmas

The effects of ion flow velocity shears parallel and perpendicular to the magnetic-field lines, which are precisely controlled by a segmented electrode, are investigated in open-ended magnetized plasmas. The perpendicular flow velocity shears are demonstrated to suppress drift-wave, flute, and ion-cyclotron instabilities. On the other hand, parallel flow velocity shears are observed to destabilize D’Angelo mode, drift-wave, and ion-cyclotron instabilities depending on the sign of the parallel shear. The combined effects of the parallel and perpendicular flow shears will be important for controlling instabilities in magnetized plasmas.

Magnetohydrodynamics in type-II superconductors: Application to force-free configurations

The magnetohydrodynamics (MHD) equations in a type-II superconductor are reexamined in view of studying the unstable kink modes in nearly-force-free configurations by taking into account the pinning effects. It appears that at the early stage these modes cannot develop against the pinning forces unless the vortices experience an externally driven Bean-London motion. When the modes have perturbed the driving forces by an amount of the order of the pinning force, they escape the latter and undertake a faster growth determined by the viscosity. However, if the magnetic energy reservoir driving the MHD instabilities is not sufficient to reach that second regime, the considered instabilities may be considered harmless. This finally leads to an estimation of the maximum electrical current that may be carried by a superconducting wire immersed in a parallel magnetic field. This critical current, which may be much larger than the Kruskal-Shafranov limit triggering the kink instabilities in magnetized plasmas, is found to be compatible with experimental data available in the literature.

A fluid–kinetic hybrid electron model for electromagnetic simulations

A fluid–kinetic hybrid electron model for electromagnetic simulations of finite-β plasmas is developed based on an expansion of the electron response using the electron–ion mass ratio as a small parameter. (Here β is the ratio of plasma pressure to magnetic pressure.) The model accurately recovers low frequency plasma dielectric responses and faithfully preserves nonlinear kinetic effects (e.g., phase space trapping). Maximum numerical efficiency is achieved by overcoming the electron Courant condition and suppressing high frequency modes. This method is most useful for nonlinear kinetic (particle-in-cell or Vlasov) simulations of electromagnetic microturbulence and Alfvénic instabilities in magnetized plasmas.

Role of transverse velocity-shear on collisional drift-wave instability in magnetized plasmas

The effect of sheared poloidal flow on collisional drift-wave instability of magnetized plasma is studied. It is shown that transverse flow shear considerably reduced the growth of the instability. A finite but small amount of viscosity completely stabilized the mode.

Zonal flow generation by parametric instability in magnetized plasmas and geostrophic fluids

Two-dimensional magnetized plasmas and geostrophic fluids exhibit a common nonlinearity due to the advection of vorticity. It is shown here that due to this nonlinearity, the propagation of small scale wave packets is accompanied by instability of a low frequency, long wavelength component. This instability is the coherent hydrodynamic generalization of the resonant type mean flow instability identified recently [P. H. Diamond, M. N. Rosenbluth, F. L. Hinton, M. Malkov, J. Fleischer, and A. Smolyakov, 17th IAEA Fusion Energy Conference, IAEA-CN-69/TH3/1, Yokohama, 1998 (to be published, International Atomic Energy Agency, Vienna)]. The mechanism discussed here, along with the resonant type, constitutes the “hydrodynamic” and “kinetic” regimes of the same process, similar to the case of plasma-beam instabilities. It is suggested that this generic mechanism is responsible for the generation of mean flow in atmospheres of rotating planets and magnetized plasmas.

Flow-curvature effect on linear Rayleigh–Taylor instability in magnetized plasmas

The effect of sheared poloidal flow on the linear Rayleigh–Taylor (RT) instability of magnetized plasma is reexamined. In the weak curvature flow limit (V⊥0″≪1) the linear RT mode stabilization effect is recovered. In the strong flow curvature limit (V⊥0″≫1) it is shown that the RT mode may not stabilize.

Consequences of the plasma-maser instability in magnetized plasma

The total momentum and energy conservation relations for the plasma-maser interaction among the resonant, nonresonant modes, and the electrons are satisfied for magnetized plasma. The Manley-Rowe relation in its original form is violated because the resonant electrons carry nonlinear momentum and energy. The plasma-maser satisfies the generalized Manley-Rowe relation which includes the effective action from resonant electrons in addition to the original one from waves. It is shown that the plasma-maser effect works if there are Onsager symmetry breaking factors such as temperature anisotropy due to external magnetic field, inhomogeneity due to density gradient. The generation mechanism of the electromagnetic radiation is studied based on the plasma-maser interaction among the electrostatic lower hybrid turbulences, accelerated electrons and extraordinary mode radiation. The theory agrees with the most striking and new features of the observation of the auroral kilometric radiation (AKR) in that the AKR bursts are observed at frequencies well above the local electron gyrofrequency.

Decay of the ion-cyclotron instability in magnetized plasmas with thermally anisotropic minority ions

It is well known that the temperature anisotropy of either the minority or majority species in a two-component plasma can make the electromagnetic ion-cyclotron mode unstable. This instability may be particularly relevant in tokamak experiments where high-power ion-cyclotron resonance heating (ICRH) is used to create an energetic population of minority ions. We investigate the nonlinear stability of this mode and show that it may decay by coupling with the sound waves supported by the two species or by a modulational decay into sideband waves.

Finite-? effects on the radiative thermal instability in magnetized plasmas

The radiative thermal instability is investigated taking into account finite-β, or electromagnetic, effects. The two-fluid model for magnetized plasmas together with the Maxwell equations are used to derive a general dispersion relation valid for compressional perturbations with frequency below the electron-cyclotron frequency. The growth rates of the radiative thermal instabilities involving fast magnetosonic flute-like and low-frequency hydromagnetic perturbations are presented.

Reply [to “Comment on ‘A transverse Kelvin‐Helmholtz instability in magnetized plasma’ by P. Kintner and N. D'Angelo”

Reply [to “Comment on ‘A transverse Kelvin‐Helmholtz instability in magnetized plasma’ by P. Kintner and N. D'Angelo”

Comment on ‘A transverse Kelvin‐Helmholtz instability in magnetized plasma’ by P. Kintner and N. D'Angelo

Comment on ‘A transverse Kelvin‐Helmholtz instability in magnetized plasma’ by P. Kintner and N. D'Angelo

Waves and Instabilities in a Magnetized Plasma

Work on computer simulation of waves and instabilities in magnetized plasmas is reviewed. Included are verification of linear theory. Particular emphasis is given to investigation of nonlinear processes involved in the saturation of instabilities and of wave damping; these include a nonlinear cyclotron resonance and particle trapping in intense waves.

Parametrically driven low-frequency waves in current carrying plasmas

The effects of the particle drift motion upon the development of low-frequency parametric instabilities in magnetized plasma are studied.

Parametric Instabilities in Magnetized Plasma

The theory of parametric instabilities driven by a finite wavenumber general pump wave is developed for homogeneous magnetized plasma. The pump wave as well as the decay products can be electrostatic as well as electromagnetic. This formalism is applied to describe lower hybrid decay into electromagnetic modes. A separate treatment for the all electrostatic wave case is given using the particle drift equations. In particular the resonant decay instabilities and the oscillating two stream instabilities are studied.

The double parametric instability in magnetized plasma

The possibility of reducing the threshold of the low-frequency parametric instability in a magnetized plasma by means of the double parametric resonance has been investigated. One finds that, besides the lowering of the instability threshold for gamma >> Omega (already reported for an unmagnetized plasma) an important reduction of the threshold-with a corresponding increase in the instability increment-results for a magnetized plasma for gamma << Omega .

Stimulated compton scattering in a plasma in magnetic field

Stimulated-Compton-scattering instabili t ies ill which electromagnetic waves are back scattered by bunches of particles rather than by coherent plasma waves have been of recent interest in laser fusion and ionospheric-heating experiments (1,2). For homogeneous unmagnetized plasmas, it has been shown by computer simulations (2,3) tha t st i lnulated-Compton-scattering instabili t ies call be impor tant in comparison to s t imulated Raman and Brillouin scattering instabilities. In this letter we consider stimulated-Compton-scattering instabilit ies in magnetized plasmas, such as the ionosphere and sonic laboratory plasmas (4), as well as laser fusion plasmas where magnetic fields are spontaneously generated (5). First, we consider the case in which the pump (~o0, k0) arid the scattered {w_ = ~--O~o, k_ = k k o ) electromagnetic waves are circularly polarized and propagating parallel to the magnetic field B0~. Here, st i inulated-Compton-scattering instabilit ies can occur when the phase velocity ~/k of the low-frequency electrostatic per turbat ions is of the order of the electron or ion thermal vclocites v~ and v~. In this ease the dispersion relat ion for co0>>(%~, co, with e)v. being the electron plasma frequency, is (6.v)

Brillouin backscattering instability in magnetized plasmas

The decay of a circularly polarized electromagnetic wave propagating parallel to an external magnetic field into another circularly polarized electromagnetic wave and an ion acoustic wave in a homogeneous plasma is considered.

Scattering and Modulational Instabilities in Magnetized Plasmas

The decay of a high-frequency wave into a scattered and an electrostatic wave is investigated for a homogeneous magnetized plasma. For wave propagation in arbitrary directions, an equation for the scattered wave is obtained accounting for the effect of the non-linear current density produced by the three-wave interaction process. As an illustration, the propagation of electromagnetic waves perpendicular to the external magnetic field is considered. The growth rates and thresholds for the stimulated scattering and modulational instabilities are obtained. The influence of a weak inhomogeneity is also considered.