Ion Cyclotron Drift Research Articles

Generation of O-Mode in the Presence of Ion-Cyclotron Drift Wave Turbulence in a Nonuniform Plasma

This study aims to investigate the effect of ion-cyclotron drift wave turbulence on the generation of ordinary mode (O-mode) in the presence of density and temperature gradients. For this, a Vlasov plasma is considered where a resonant, and non-resonant modes are considered to be present in the system. Here, the non-resonant mode is a perturbation caused by O-mode in a quasi-steady state of plasma, which is characterised by the presence of low frequency ion-cyclotron resonant mode waves. The interaction between these waves is studied by the Vlasov-Maxwell set of equations and a modified Maxwellian-type distribution function for particles that includes the external force field and associated density and temperature gradient parameters . The study analyses the growth rate of electromagnetic O-mode at the expense of ion-cyclotron drift wave energy and the associated impact of the density and temperature gradient. This model uses the linear response theory on weakly turbulent plasma, evaluates the responses due to turbulent and perturbed fields, and obtains the nonlinear dispersion relation for O-mode.

Obliquely propagating electromagnetic drift ion cyclotron instability

Identification of wave characteristics during current disruption events in the near‐Earth geomagnetic tail region is important for understanding the substorm onset mechanism. The present paper discusses a linear stability analysis in the ion cyclotron frequency range of a plasma possessing the temperature anisotropy and cross‐field flow. It is found that the ion cyclotron drift waves propagating in quasi‐perpendicular direction with respect to the ambient magnetic field are characterized by low frequencies (ω ≲ 0.5Ωi), while quasi‐parallel waves have frequencies close to the ion cyclotron frequency (ω ∼ Ωi). This finding is consistent with the observation by THEMIS spacecraft of a current disruption event in which similar high‐ and low‐frequency band structures are present. The interpretation of the low‐frequency mode as the quasi‐perpendicular mode is consistent with a recent data analysis. The present paper shows that the high‐frequency quasi‐parallel mode can simultaneously be excited with the low‐frequency quasi‐perpendicular mode.

Effect of Non-Thermal Electrons on the Interaction of Drift Wave and Electrostatic Ion-Cyclotron Wave and Modulation Instability

We have analysed the effect of non-thermal electrons on the interaction between the electrostatic ion-cyclotron wave and drift wave, taking into account the low frequency ponderomotive force. It is observed that one of the equation is a generalisation of the famous Hasegawa-Mima form with a non-zero right hand side representing interaction with ion cyclotron wave. In the second part we have treated only the drift wave equation in the non-interacting limit and have obtained exact vortex like solutions. Lastly, the modulational instability of the drift wave is studied in the non-interaction limit, by deriving a non-linear Schrodinger equation.

Excitation of Azimuthally Propagating Ion-Cyclotron Drift Waves in Large Magnetized Plasma

The dispersion relations of ion-cyclotron drift waves strongly depend on both the axial and azimuthal wave numbers as well as the radial gradient of the plasma density. The dispersion surfaces of the waves have been shown graphically in order to determine the characteristics of ion-cyclotron drift waves. The azimuthally propagating electrostatic waves have been excited externally by a mesh grid in a large-diameter magnetoplasma. The measured azimuthal dispersion relations agree with the theoretical ones of ion-cyclotron drift waves.

Ion Cyclotron Drift Waves in Plasmas with Controlled Radial Density Distributions

The ion cyclotron drift wave (ICDW), which is the mode coupled between the electrostatic ion cyclotron wave and the drift wave, was investigated by experiments and calculations. The calculated dispersion relations for the m=1 mode show that the mode coupling becomes stronger with increasing |κ| (where κ=dn/dr/n) and a resonance aroud the ion cyclotron frequency changes to a cutoff when |κ| exceeds the azimuthal wave number ky. A simple method to control the radial density distribution is proposed and is confirmed to be varied to a considerable extent. Ion cyclotron drift waves for the m=1, m=-1 and m=2 modes have been excited externally with controlled values of |κ|. The measured dispersion relations agree with the theoretical predictions.

Influence of RF on ion drift dissipative instabilities

Ion drift and ion cyclotron drift waves have been observed in the density gradient of a plasma column. Launching RF near the lower hybrid frequency into the plasma results in a suppression of the ion drift waves and a parametric amplification of the ion cyclotron drift waves. Spectral analysis of probe signals monitoring the plasma density fluctuations demonstrates the importance of three wave coupling for the saturation of the observed instabilities.

Detection of an ion cyclotron instability

In the density gradient of a dc discharge unstable modes are observed at frequencies 0<ω<ω ci. Spectral analysis of two probe signals, monitoring the plasma density fluctuations, identifies the modes as an ion cyclotron drift instability and shows active three-wave coupling between several modes of the spectrum.

External excitation of ion cyclotron drift waves in a two-ion species plasma

Ion cyclotron drift waves propagating across a density gradient and a magnetic field have been excited externally in a two-ion species plasma, with its concentration ratio controlled. The measured dispersion relations agree with the theoretical predictions.

Field‐aligned currents in the Earth's magnetotail

Three field‐aligned current sheets are directly observed with plasma and magnetometer instrumentation on board the ISEE spacecraft located at ∼20 RE in the postmidnight sector of the magnetotail. These current sheets are encountered at the northern plasma sheet boundary as the plasma sheet expanded past the spacecraft positions during the recovery phase of a magnetic substorm. This expansion speed, Vz in solar magnetospheric coordinates, is 14 km/s. The corresponding convection electric fields E⊥ are derived from the three‐dimensional proton velocity distributions as measured with the quadrispherical Lepedea plasma instrumentation. The average current densities within the three field‐aligned current sheets are +3.3 × 10−9, −1.3 × 10−8, and +1.1 × 10−8 A/m², in order of decreasing distance to the plasma sheet. Current densities in the first and third sheets are directed into the ionosphere, and the current carriers are ionospheric electrons drifting away from the ionosphere. The second, or central, current sheet is directed away from the ionosphere; however, the source of the current‐carrying electrons is unclear. This central current sheet is thought to be associated with ionospheric electron precipitation producing discrete auroral arcs via an acceleration mechanism at intermediate altitudes. The thicknesses of the three magnetotail current sheets are 0.36, 0.55, and 0.74 RE, again in order of decreasing distance from the plasma sheet. Current intensities, the products of current densities and sheet thicknesses, of the field‐aligned current sheets are measured simultaneously with magnetometers and are +0.010, −0.028, and +0.018 A/m, respectively. These values agree reasonably well with those derived from the direct plasma measurements. Electron drift velocities VD within the current sheets are in the range 0.05 to 0.1 Ve, where Ve is the electron thermal velocity. The ion sound velocity Cs ≃VD. These plasma parameters, including the fact that the protons are hot with Tp ≃3Te, appear to provide an unfavorable situation for any substantial steady state anomalous resistivity at this location of the magnetotail. Current‐driven ion cyclotron and/or ion cyclotron drift instabilities may be responsible for broadband electrostatic noise previously observed at the boundary of the plasma sheet.

Parametric decay into ion cyclotron waves and drift waves in multi-ion species plasma

Parametric decay processes near the ion cyclotron frequency are investigated experimentally and theoretically in multi-ion species plasmas. The relevant theoretical dispersion relation of the parametric coupling is derived, including the ion drift motion. Experimental data obtained in the Princeton L-4 device verify these theoretical predictions in some detail. In a helium-neon plasma, the relative ion drift motion excites electrostatic ion cyclotron waves (the kinetic ion-ion hybrid mode) when ω0≳ΩHe +ΩNe. In a region of large density gradient, the ion drift motion also excites low-frequency drift waves when ω0≳ΩHe+ω*. The experimental data are found to agree well with the theory. The relevance of these processes to ion cyclotron heating of fusion plasmas is discussed.

Current-driven instabilities and resultant anomalous effects in isothermal, inhomogeneous plasmas

The evolution and effects of current-driven instabilities in isothermal, inhomogeneous plasmas are investigated in both theory and experiment. Sucessive destabilizations of four different instabilities, low-frequency drift wave, ion-cyclotron drift wave, high-frequency (continuous-spectrum ion-cyclotron) drift wave, and high-frequency electron wave, are observed in Q-device plasmas with increased current, and explained by a theory based on fluid and kinetic equations. Anomalous effects resulting from wave-particle interactions, i.e., enhanced resistivity, ion heating, and electron viscosity, are compared with predictions based on quasi-linear calculations. Analogous to ion sound causing important anomalies in the transport coefficients for plasmas with Te/Ti≫1, high-frequency, continuous-spectrum drift waves determine anomalous plasma behavior in inhomogeneous plasmas with Te/Ti≃1.

Density gradient drift instabilities: Oblique propagation at zero beta

The linear Vlasov dispersion relation for electrostatic instabilities driven by a cross field current due to a density gradient in a unidirectional magnetic field is examined in the local approximation. Both electrons and ions are taken as magnetized, and propagation is in the plane defined by the drift velocity and the magnetic field. Three instabilities are studied and compared: the lower hybrid drift, ion cyclotron drift, and the universal drift instability. Thresholds and properties at oblique propagation are studied for a wide range of drift speeds and Te/Ti ratios. Each of these modes propagates at sufficiently oblique angles to prevent stabilization due to finite length in typical linear theta pinches greater than several hundred ion gyroradii in length.

Ion Cyclotron Drift Instability Driven by Cross-Field Electron Current and Plasma Heating

The ion cyclotron drift instability can be excited by a cross-field current due to E r × B drift of electrons when a strong radial electric field E r is produced in an inhomogeneous plasma column under a weak magnetic field B by applying a dc voltage between a cathode and a heating anode of hollow cylindrical type. Experintental results of the instability are well explained by the dispersion equation, where a negative energy wave of a drifting electron beam interacts with the ion Bernstein wave in the background plasma. As the instability is developed, considerable heating of ions and electrons is observed in the perpendicular and parallel direction to B , respectively.

Lower hybrid drift instability at low drift velocities

The behavior of the lower hybrid drift instability is investigated in the low drift velocity regime by including the effects of the magnetic field on the ions. It is found that the mode is transformed from the nonresonant lower hybrid drift instability to the resonant ion cyclotron drift instability as the drift velocity Vd decreases and is finally stabilized when Vd/Vti∼ (me/mi)1/2.

Electrostatic ion cyclotron instabilities driven by parallel ion beam injection

The detailed identification of two instabilities driven by an ion beam injected parallel to the confining magnetic field, a resonant ion cyclotron instability, and a nonresonant ion cyclotron drift wave driven by the density gradient of the beam, is reported. Experimental results are in good agreement with numerical calculations based on the kinetic Vlasov equations. Quasi-linear velocity space diffusion of the beam ions by wave-particle interaction is observed, demonstrating enhanced energy transfer. The relevancy of these results to tokamak neutral beam injection heating is discussed.

Ion cyclotron drift instability driven by cross-field current

An ion cyclotron drift instability is excited by a cross field current due to E r × B drift of electrons and ion heating is observed in a plasma column in a magnetic field when a dc radial electric field E r is applied.

Identification of Ion-Cyclotron Drift Instability with Discrete and Continuous Spectra

Identification of Ion-Cyclotron Drift Instability with Discrete and Continuous Spectra

The ion cyclotron drift loss-cone instability with a coexisting cold plasma

The stability condition of an ion cyclotron drift loss-cone wave (non-flute mode) in a non-uniform plasma with a coexisting cold plasma is considered. It is shown that the presence of low energy components in the plasma may significantly affect the stability criteria of these ion cyclotron waves. Furthermore, perturbations at frequencies which are multiples of the ion cyclotron frequency may be destabilized when the number density of high energy protons exceeds the critical value that is determined by the number density of cold plasma and the strength of field inhomogeneity.

Ion-cyclotron drift instability in a finite-\U0001d6c3 plasma

The author investigates the possibility of the build-up of ion-cyclotron perturbations in an inhomogeneous plasma having a finite ratio between its pressure and the pressure of a magnetic field. It is shown that the plasma is more stable with respect to such perturbations at finite pressure than at zero pressure. The stabilization is associated with a smearing of the cyclotron resonance resulting from the velocity dependence of the magnetic drift of the ions; it is also linked with Landau damping in the electrons, the magnetic drift of which coincides with the wave phase velocity.

The ion cyclotron drift loss-cone instability in mirror magnetic wells

The ion cyclotron drift loss-cone instability is studied for the case of steep particle density gradients [(1/n)(dn/dr) ai ≃ −0.3], magnetic field gradients and finite plasma dimensions. Computational results show that there are no high density stable regimes. It is found that for a mirror velocity distribution the magnetic well field gradient is de-stabilizing, in contrast to the stabilizing effect found by Krall and Fowler for a near-Maxwellian velocity distribution. Potential distributions and critical densities are found for a slab model using appropriate boundary conditions to determine the modes. The threshold densities for the boundary value case are only slightly higher than that given by the usual local approximation. Frequencies and growth rates as functions of azimuthal wave number are found for the instability for typical PHOENIX II and ALICE parameters.