Whistler instability in a semi-relativistic bi-Maxwellian plasma

Employing linearized Vlasov–Maxwell system of equations, the whistler instability is discussed for a semi-relativistic bi-Maxwellian distribution. The dispersion relations are analyzed analytically along with the graphical representation and the estimates of the growth rate and instability threshold condition are also presented in the limiting cases i.e., _ξ±=(ω?Ω)/_k∥vt‖?1${\xi }_{\pm }=(\omega ?\Omega )/k_{\parallel }{v}_{t_{\Vert }}?1$ (resonant case) and _ξ±?1${\xi }_{\pm }?1$ (non-resonant case). Further for field free case i.e., _B0=0$B_0=0$, the growth rates for Weibel instability in a semi-relativistic bi-Maxwellian plasma are presented for both the limiting cases.     

Precession of an electron-magnetohydrodynamic field-reversed configuration

A field-reversed configuration is generated in a large laboratory plasma in the parameter regime of electron magnetohydrodynamics. During its free relaxation, the magnetic moment is observed to precess when tilted from its original axis. The precession velocity is the electron drift velocity in the toroidal current layer. The precession is a manifestation of frozen-in field lines in a moving electron fluid.     

Chaotic scattering and self-organization in spheromak sustainment

Flux core spheromak sustainment by electrostatic helicity injection is studied in resistive MHD. The geometry has magnetized electrodes at the ends held at a potential difference V. For V>V(c) the central current column is kink unstable. The nonlinear state with V just above V(c) has a large volume of flux surfaces, with rotational transform provided by the helical kinking of the column. As V increases the kink becomes stronger, the tori are destroyed, and the field lines exhibit chaotic scattering. The distribution of field line lengths L, related to confinement and parallel current density, is studied. At larger V or larger Lundquist number S, a limit cycle appears.     

Experimental identification of the kink instability as a poloidal flux amplification mechanism for coaxial gun spheromak formation

The magnetohydrodynamic kink instability is observed and identified experimentally as a poloidal flux amplification mechanism for coaxial gun spheromak formation. Plasmas in this experiment fall into three distinct regimes which depend on the peak gun current to magnetic flux ratio, with (I) low values resulting in a straight plasma column with helical magnetic field, (II) intermediate values leading to kinking of the column axis, and (III) high values leading immediately to a detached plasma. Onset of column kinking agrees quantitatively with the Kruskal-Shafranov limit, and the kink acts as a dynamo which converts toroidal to poloidal flux. Regime II clearly leads to both poloidal flux amplification and the development of a spheromak configuration.     

Dissipative instability in an aerosol plasma

Dissipative instability in a weakly ionized aerosol plasma has been studied with allowance for a finite electric conductivity of the medium, electron and ion diffusion, and friction of the aerosol component against a neutral gas. Instability is caused by the relative drift of the aerosol and ion components. Estimates of the basic parameters of instability (threshold, characteristic wavelengths, and increments) in experiments with dust crystals indicate that this instability can be an important additional factor upon the formation of regular structures in an aerosol plasma.     

Suppression of MHD fluctuations leading to improved confinement in a gun-driven spheromak

Magnetic fluctuations have been reduced to approximately 1% during discharges on the Sustained Spheromak Physics Experiment by shaping the spatial distribution of the bias magnetic flux in the device. In the resulting quiescent regime, the safety factor profile is nearly flat in the plasma and the dominant ideal and resistive MHD modes are greatly reduced. During this period, the temperature profile is peaked at the magnetic axis and maps onto magnetic flux contours. Energy confinement time is improved over previous reports in a driven spheromak.     

Whistler detrapping from a density crest duct

A theory of whistler wave leakage from a magnetic field aligned duct with enhanced plasma density is presented. The energy flux from the duct and the corresponding wave attenuation rate are calculated in the WKB approximation. Possible experimental confirmations of the theory are indicated.     

Dust-acoustic instability in an inductive gas-discharge plasma

Spontaneous excitation of a dust-particle density wave is observed in a dust cloud levitating in the region of the diffused edge of an rf inductive low-pressure gas-discharge plasma. The main physical parameters of this wave and of the background plasma are measured. The analytic model proposed for the observed phenomenon is based on the theory of dust sound and successfully correlates with experimental data in a wide range of experimental conditions. The effect of variable charge of dust particles on the evolution of the observed dust-plasma instability is studied analytically. It is shown that the necessary condition for the development of the dust-acoustic instability is the presence of a dc electric field in the dust cloud region.     

Magnetic instability in an inhomogeneous plasma in an intense electromagnetic wave

Radiophysics Research Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 33, No. 2, pp. 170–176, February, 1990.