Current-driven Electrostatic Ion-cyclotron Instability Research Articles

Effect of dust charge fluctuations on current-driven electrostatic ion-cyclotron instability in a collisional magnetized plasma

Current-driven electrostatic ion-cyclotron (EIC) instability is studied in a collisional magnetized dusty plasma. The growth rate and unstable mode frequencies were evaluated based on existing physical parameters relevant to ion cyclotron waves in dusty plasmas. It is found that the unstable mode frequency and growth rate of current-driven EIC instability increase with δ (ion-to-electron density ratio). Moreover, the increase in electron neutral collisional frequency (νe) has no effect on the unstable mode frequency while the normalized growth rate has linear dependence on νe.

Ion-cyclotron instability in current-carrying Lorentzian (kappa) and Maxwellian plasmas with anisotropic temperatures: A comparative study

Current-driven electrostatic ion-cyclotron instability has so far been studied for Maxwellian plasma with isotropic and anisotropic temperatures. Since satellite-measured particle velocity distributions in space are often better modeled by the generalized Lorentzian (kappa) distributions and since temperature anisotropy is quite common in space plasmas, theoretical analysis of the current-driven, electrostatic ion-cyclotron instability is carried out in this paper for electron-proton plasma with anisotropic temperatures, where the particle parallel velocity distributions are modeled by kappa distributions and the perpendicular velocity distributions are modeled by Maxwellian distributions. Stability properties of the excited ion cyclotron modes and, in particular, their dependence on electron to ion temperature ratio and ion temperature anisotropy are presented in more detail. For comparison, the corresponding results for bi-Maxwellian plasma are also presented. Although the stability properties of the ion cyclotron modes in the two types of plasmas are qualitatively similar, significant quantitative differences can arise depending on the values of κe and κi. The comparative study is based on the numerical solutions of the respective linear dispersion relations. Quasilinear estimates of the resonant ion heating rates due to ion-cyclotron turbulence in the two types of plasma are also presented for comparison.

Current-driven ion cyclotron instability of multicomponent field-aligned sheared flow

The effect of velocity shear of the magnetic field-aligned plasma flow on excitation of the current-driven electrostatic oxygen ion cyclotron instability in the presence of hydrogen ions is considered by using kinetic formalism. It is shown that an increase of velocity shear as well as relative concentration of oxygen ions lead to a decrease of the instability threshold. The influence of the relative concentration of oxygen ions and velocity shear on the growth rate is investigated. For a weak velocity shear the growth rate decreases with reducing of the oxygen concentration, however for a strong shear the growth rate due to the presence of hydrogen ions may increase.

Shear-flow-driven ion cyclotron instabilities of magnetic field-aligned flow of inhomogeneous plasma

The effect of magnetic field-aligned flow with a transverse flow velocity gradient (velocity shear) on the generation of electrostatic ion cyclotron waves is studied analytically by using kinetic formalism. It is shown that flow shear not only modifies the frequency and growth rate of a known current-driven electrostatic ion cyclotron instability (CDEIC), but is the source of the development of specific kinetic and hydrodynamic shear-flow-driven ion cyclotron instabilities at the levels of current along the ambient magnetic field, which is subcritical for the development of the CDEIC instability.

Electrostatic Potential Formation.

Numerical simulation is a powerful tool for investigating the formation of electric potential structure in plasmas. By means of a self-consistent open boundary two-and-a-half-dimensional particle simulation model, it is demonstrated that a V-shaped dc potential structure is created by a current-driven electrostatic ion-cyclotron instability. A potential difference along the magnetic field is generated by anomalous resistivity. This difference becomes larger for a longer system along the magnetic field; thus, the potential difference may become several kV for a thousand km anomalous resistivity region.

Open boundary particle simulation of electrostatic ion cyclotron instability

We have developed a 2½-dimensional open boundary particle simulation model and have studied the current-driven electrostatic ion-cyclotron instability and related d.c. potential difference. Fresh streaming electrons are injected smoothly from the boundaries at each time step, avoiding unphysical accumulation of charged particles in front of the boundaries. As a current-driven electrostatic ion cyclotron instability grows, a d.c. potential difference along the magnetic field lines is created.

Velocity‐shear origin of low‐frequency electrostatic ion‐gyroresonant waves

Electrostatic ion‐cyclotron waves with spectral features below the ion gyrofrequency and spaced by small fractions of the ion gyrofrequency are reported, a result not possible for waves associated with the well‐known current‐driven electrostatic ion‐cyclotron (CDEIC) instability. This is accomplished by producing a localized, transverse (to the magnetic field B ž) electric field E(x) x) in a laboratory plasma to excite inhomogeneous energy‐density driven (IEDD) waves and by exploiting the kyνE dependence of the IEDD mode frequency, where ky and νE are the components of the IEDD wavevector and plasma drift speed, respectively, along the E × B direction. The IEDD frequency range is shown to reach down to one‐third of the ion gyrofrequency, a range usually reserved for other types of waves, e.g., ion‐acoustic waves. These results may be relevant to broadband ELF waves observed in the ionosphere.

V-Shaped dc Potential Structure Caused by Current-Driven Electrostatic Ion-Cyclotron Instability

It is first demonstrated that a V-shaped dc potential structure is created by a current-driven electrostatic ion-cyclotron instability by means of an open two-dimensional particle simulation model. A positive dc potential difference along magnetic field lines is generated by anomalous resistivity caused by the ion-cyclotron instability. In the direction across the magnetic field lines, the dc potential rises from the high-current region to the low-current region. {copyright} {ital 1997} {ital The American Physical Society}

Electrostatic ion-cyclotron wave experiments in the WVU Q machine

The influence of transverse, localized, DC electric fields (TLEs) on the current-driven electrostatic ion-cyclotron (CDEIC) instability is being investigated in a Q machine. A small (diameter approximately 10 ion gyroradii) segmented disk electrode is being used to excite the mode in a narrow electron-current channel along which exists a radial electric field between regions that magnetically map to the different circular segments (separated by a radial gap of approximately 3 ion gyroradii). Experiments aimed at demonstrating a TLE dependence in the threshold current for mode excitation are described. A comparison of observed and predicted mode frequencies over a range of magnetic field strengths is presented for the benchmark case of no applied transverse electric field. When the electric field is present, ion-cyclotron fluctuations are observed for cases in which the current is below the CDEIC instability threshold. >

On the current-driven electrostatic ion-cyclotron instability: a review

Theoretical, numerical, and experimental investigations of the electrostatic ion-cyclotron instability (EICI) are critically reviewed. The discussion of theory focuses mainly on the linear theories, with particular attention to those that have been used in explaining experimental observations, but a short account of various nonlinear theories is also given. Numerical simulation results are surveyed. Experimental investigations in Q-machine plasmas and their interpretation in terms of various theories are then examined.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

On the mechanism of the electrostatic ion cyclotron instability

Experimental investigations in a new arrangement in a single-ended collisionless Q-machine shed new light on the mechanism of the current-driven electrostatic ion cyclotron instability. The instability was excited by a positively-biased button surrounded by a coplanar usually floating ring electrode. By inserting an appropriately biased additional grid with central hole the plasma density between the ring and this grid could be controlled while the current channel in front of the button was not perturbed. Also in this arrangement the potential relaxation instability could be excited. By varying the bias and the distance of the grid-hole electrodes from the ring-button a smooth transition from a regime dominated by the potential relaxation instability to one dominated by ion cyclotron instability was obtained. In addition, the role of the reflected ions for the mechanism of the electrostatic ion cyclotron instability could be seen in a new light.

An experimental investigation on the influence of neutral collisions on the current-driven electrostatic ion-cyclotron instability

An experimental investigation on the influence of ion/electron-neutral collisions on the electrostatic ion-cyclotron instability was performed in a single-ended Q-machine plasma. The collision frequency was controlled by varying the neutral back-ground pressure between 10−4 Pa and 1 Pa. Various noble gases (He, Ar, Kr and Xe) and nitrogen were employed. In all cases the instability was almost quenched when the neutral background pressure passed a critical value which increased for decreasing cross-section of ion-neutral collisions. The ion-neutral collision frequency at this critical pressure was much smaller than the ion gyrofrequency. However, the mean free path at critical pressure was shorter than the length of the plasma column. Under these conditions the results are consistent with the interpretation of the ion-cyclotron instability as a two-dimensional potential relaxation oscillation.

Effects of electron heating on the current driven electrostatic ion cyclotron instability and plasma transport processes along auroral field lines

Fluid simulations of the plasma along auroral field lines in the return current region have been performed to show that the onset of electrostatic ion cyclotron (EIC) related anomalous resistivity and the consequent heating of electrons leads to much higher transverse ion temperature than the current driven EIC instability (CDICI) alone would produce. Anomalous resistivity enhances ion heating in two ways: (1) by inhibiting the growth of the critical electron‐ion drift velocity, VcH, which must be exceeded to excite the EIC instability and (2) by increasing the relative drift velocity between the electrons and the ions, VD, through the formation of density cavities due to increased ambipolar electric field. The anomalous resistivity associated with the turbulence is limited by electron heating, so that CDICI eventually saturates, but at a substantially higher transverse temperature than would be the case in the absence of resistivity. This process demonstrates a positive feedback loop in the interaction between CDICI, anomalous resistivity, and parallel large scale dynamics in the topside ionosphere.

Generalized fluid model of plasma outflow processes in the topside ionosphere

The classical and anomalous transport properties of a multifluid plasma are investigated in the presence of auroral field aligned return currents, using a multimoment fluid model with anomalous transport coefficients. This approach offers the possibility of simulating large scale dynamic phenomena without neglecting the important macroscopic consequences of microscopic processes such as anomalous resistivity, turbulent heating, etc. The macroscopic effects of the electrostatic ion cyclotron (EIC) instability (perpendicular ion heating) and of an EIC-related anomalous resistivity mechanism which heats the electrons are included in the present version of the model. The responses of the outflowing ionospheric plasma to the application of current, with and without instabilities, are exhibited. The simulations show that the electron drift velocity corresponding to a return current of 0.65 μA/m 2 is above the threshold for EIC waves. The onset of EIC related anomalous resistivity enhances ion heating in two ways: (1) by inhibiting the growth of the critical electron-ion drift velocity, which must be exceeded to excite the EIC instability and (2) by increasing the relative drift velocity between the electrons and the ions, through the formation of density cavities due to increased ambipolar electric field. The anomalous resistivity associated with the turbulence is limited by electron heating, so that the EIC turbulence eventually saturates, but at a substantially higher ion transverse temperature than would be the case in the absence of resistivity. This process demonstrates a positive feedback loop in the interaction between the current driven EIC instability (CDICI), anomalous resistivity, and parallel large scale dynamics in the topside ionosphere.

Determination of the frequency-controlling region of the current-driven electrostatic ion-cyclotron instability

A small, axially moveable test coil is used to locally increase the magnetic field of a single-ended Q-machine. The influence of this additional field on the current-driven electrostatic ion-cyclotron instability (EICI) depends on its distance from the collector. Three different regions are found, and in the middle region, at a distance of several cm from the collector, the local magnetic field determines the instability frequency and amplitude along the entire column. When the local increased magnetic field is in the region nearest to the collector, however, the EICI is damped and its frequency is decreased.

Selective destabilization of ion cyclotron modes

Observations of the current-driven electrostatic ion cyclotron instability, both at Te/Ti=1 and Te/Ti>>1, show that as the normalized wave number, kperpendicular to rho i is varied, different modes (m=1, 2, 3...) become successively the most unstable mode. The calculated values of kperpendicular to rho i at which the cross-over from one mode to the next occurs are in reasonable agreement with the observed values provided that the local density gradient is taken into account.

Stabilization of the Current-Driven Electrostatic Ion-Cyclotron Instability by Lower-Hybrid Waves

The current-driven electrostatic ion-cyclotron instability in a $Q$ machine operated in the low-density regime ${(\frac{{\ensuremath{\omega}}_{\mathrm{pe}}}{{\ensuremath{\omega}}_{\mathrm{ce}}})}^{2}\ensuremath{\ll}1$ is stabilized by externally generated rf electrostatic fields in the lower-hybrid range. Stabilization is due to a resonant ponderomotive force, which reduces the instability frequency, thus increasing the ion-cyclotron damping. The experimental results are in good agreement with an analysis which describes the effect of rf power on the instability frequency shift and growth rate.

Ion fluctuations and velocity distribution in the presence of ion cyclotron waves

Ion density fluctuations and the ion velocity distribution function in the presence of the current-driven electrostatic ion cyclotron instability are determined using resonance fluorescence of the ions. The optical line intensity modulation shows that the ion density modulation can be as large as 90%. From the Doppler broadening of the lines it is found that the distribution function of ions heated by the unstable ion cyclotron waves is Maxwellian with an uncertainty of 5%.

Temporal evolution of ion temperatures in the presence of ion cyclotron instabilities

Spectroscopic techniques to determine the temporal evolution of the ion temperature in a collisionless barium plasma are presented. The theory of temperature relaxation in plasmas with external magnetic field is modified to include wave-induced collisions. Experiment and theory are compared. The current-driven electrostatic ion cyclotron instability is shown to be an effective method for wave heating of ions.

Onset, growth, and saturation of the current-driven ion cyclotron instability

The temporal evolution of the current-driven electrostatic ion cyclotron instability was investigated experimentally. The critical destabilizing electron drift velocity for different values of mode phase velocity was measured. The phase velocity was changed by varying the effective plasma column length and hence the parallel wavelength. Ion cyclotron damping was observed to dominate over electron Landau damping at low phase velocities. The temporal growth rate was experimentally determined for several values of electron drift and found to agree very well with linear theory. The observed saturated mode amplitudes compare favorably with the saturation levels predicted by a theory of nonlinear stabilization due to wave induced collisions.