Electromagnetic Drift Research Articles

Comparison of IRI model predictions with low latitude ionospheric observations

During a period of high solar activity (1979/1980), IRI-predicted electron density profiles were compared with measurements made at Fortaleza (Brazil), 2 degrees off the dip equator. A few discrepancies were found. They are attributed mainly to dynamical effects associated with the low latitude E × B electromagnetic plasma drifts and thermospheric neutral winds that are not correctly reproduced in the CCIR numerical maps and in the IRI profile shapes as well. In particular, the dependence on the magnetic declination angle, which strongly affects the electrodynamical plasma motions at low latitudes, is not satisfactorily considered in the models.

Transition from neoclassical to turbulent electron diffusion

Electron diffusion in tokamak geometry is calculated including both the Coulomb collisional pitch angle scattering and the electromagnetic drift wave fluctuation spectrum. In the weak fluctuation limit the neoclassical banana-plateau diffusion coefficient is recovered. At higher fluctuation levels typical of the mixing length amplitude the anomalous transport formulas of drift wave turbulence are recovered using test particle simulations.

Nonlinear fluid equations for fully toroidal electromagnetic waves in nonuniform magnetized plasmas.

By means of the two-fluid model of Braginskii [Reviews of Plasma Physics, edited by M. A. Leontovich (Consultants Bureau, New York, 1965), Vol. I, p. 205], this paper derives a set of nonlinear differential equations governing the dynamics of fully toroidal low-frequency electromagnetic waves in an inhomogeneous electron-ion plasma immersed in a nonuniform magnetic field. The effects of equilibrium electron and ion pressure gradients, magnetic drifts caused by the nonuniform magnetic field, as well as the contribution of heat fluxes in the particle-energy transport equations are incorporated. In the linear limit, expressions for the ion and electron number-density perturbations together with a new dispersion relation for fully toroidal electromagnetic waves are obtained. A new long-wavelength electromagnetic drift wave instability is shown to exist in a nonuniform magne- tized electron plasma. The formation of dipolar vortices in the two-dimensional ion-temperature-gradient-driven electrostatic drift wave turbulence has been demonstrated.

Toroidal electron-temperature-gradient driven electromagnetic drift wave instability

A novel toroidal electron-temperature-gradient driven electromagnetic drift wave instability has been found in the regime where the wavelength of the oscillations is between the electron and ion gyroradii. This mode is a toroidal version of the collisionless electron-temperature-gradient driven instability. A fully toroidal fluid model has been used and a mode with a poloidal direction of propagation that depends on the ratio of the scale lengths of the density and magnetic field gradients, has been found. It is suggested that the present mode can be responsible for the soft beta limitation as well as the anomalous electron energy transport in a tokamak reactor.

A study of runaway electron confinement in the ASDEX tokamak

The results of runaway electron confinement experiments from ASDEX are analysed to elucidate the structure of electromagnetic turbulence which may cause anomalous electron heat transport in the L-mode confinement regime. From a simple model, the radial correlation length (W) of the magnetic turbulence is determined to be about 1 mm. Using this value and that of the experimentally deduced electron thermal diffusivity, the authors determine the radial magnetic fluctuation level at the plasma edge in the L-mode to be (B̃r/B0) ∼ 2 × 10−4. Scalings of W and B̃r/B0 are deduced from parameter scans. From a comparison of these results with the predictions of various theoretical models, it is concluded that skin depth turbulence, electromagnetic drift wave turbulence, rippling modes, and microtearing modes are inferior candidates and that resistive ballooning modes offer the best possibility for a consistent interpretation of the data.

ULF pulsation eigenperiods within the plasmasphere

Physically realistic ion density models are applied to calculations of toroidal mode ULF pulsation eigenperiods within the plasmasphere. The model periods reflect the dominant effect of O + ions along the shorter field lines at lower latitudes, and of H + ions in the outer plasmasphere. In the absence of electromagnetic drifts, the largest periods occur during the day. Inclusion of previously measured azimuthal electric field values retains the daytime period maximum at latitudes below ∼35°, but results in a period minimum near mid-day at higher latitudes. The latitudinal period variation has a peak value near 20° where O + is dominant, a minimum near 35° and increasing periods at higher latitudes. Geomagnetic activity is simulated by reducing the ion densities in flux tubes at latitudes greater than 50°. While the H + population is replenished from the underlying ionosphere, the model periods have a corresponding increase, as does the rate of period increase with latitude. At mid latitudes (30–40°) where neither the O + nor H + ion populations dominate, the toroidal mode higher harmonics have irregularly spaced frequencies. The Alfvén velocity distribution along the mid-latitude field lines suggests the standing wave fields, and hence mapping factors between the equatorial plane and ionosphere, could be different to those employed at higher latitudes where H + is the dominant ion.

Modeling of the planetary structure of the ionosphere and the protonosphere coupling

A planetary model of the ionosphere and the protonosphere coupling is described. The system of three-dimensional nonstationary modeling equations of continuity and motion for the ions O+ and H+ is presented. Some numerical results of model calculations are compared with the experimental data. The important role of electromagnetic drifts in the formation of large-scale morphological peculiarities of the ionosphere and the protonosphere coupling is shown.

Electron diffusion in tokamaks due to electromagnetic fluctuations

Calculations for the stochastic diffusion of electrons in Tokamaks due to a spectrum of electro-magnetic drift fluctuations are presented. The parametric dependence of the diffusion coefficient on the amplitude and phase velocity of the spectrum, and the bounce frequency for the electrons is studied. The wavenumber spectrum is taken to be a low order (5*5) randomly-phased, isotropic, monotonic spectrum extending from kperpendicular to min approximately= omega ci/cs to kperpendicular to max approximately=3 omega pe/c with different power laws of decrease phi k approximately= phi 1/km, 1<or=m<or=3. A nonlinear Ohm's law is derived for the self-consistent relation between the electrostatic and parallel vector potentials. The parallel structure of the fluctuations is taken to be such that k/sub ///nl nu e< omega k due to the nonlinear perpendicular motion of the electrons described in the nonlinear Ohm's law. The diffusion coefficient scales approximately as the neo-Alcator and Merezhkin-Mukhovatov empirical formulas for plasma densities below a critical density.

Implications of the relationship between electromagnetic drift components at mid and low latitudes

We have derived a number of relationships between the meridional and longitudinal ion drifts at low and mid latitudes that are enforced by the condition of a curl-free electric field. The application of these relationships to observations from the Jicamarca radar allow additional properties of the observations to be exposed. The results of including and excluding these properties in plasma distribution calculations are discussed. Some possible alternatives to an electrostatic potential model for the ion drifts, which allow extreme features to be included in the condition of a curl-free electric field, are also discussed.

Electromagnetic drift modes in an inhomogeneous electron gas.

A pair of nonlinear equations is derived which describes the dynamics of the electromagnetic drift oscillations in a nonuniform magnetized electron gas. It is shown that the nonlinear electromagnetic drift modes can propagate in the form of dipole vortices.

Kinetic theory of the electromagnetic drift modes driven by pressure gradients

Kinetic equations for the electromagnetic drift modes are derived and analyzed for the stability of tokamaks in the local approximation. In the dissipationless, hydrodynamic limit, the fifth-order polynomial dispersion relation previously studied is recovered. The kinetic velocity space integrals in the ion dynamics are shown to modify the five principal modes of oscillation and their polarizations. It is shown that in kinetic stability theory the critical plasma pressure defined in magnetohydrodynamic theory determines a transition from microinstability to macroinstability.

Computer simulations of the ionospheric equatorial anomaly in East Asia for equinoctial, solar minimum conditions. Part I—Formulation of model

A new quasi three-dimensional, time-dependent meridional continuity equation for ionization in the ionospheric F-region, taking into account production, loss, electromagnetic and wind drifts, has been derived. This was coupled to the momentum equations for horizontal neutral winds so as to obtain a self consistent solution for the effects of neutral winds on the low-latitude distribution of ionization throughout East Asia. For simplicity, the non-linear inertia terms have been neglected in the wind calculations. The numerical scheme used for solving the coupled equations is given and the selection of input parameters to the numerical model discussed.

Electromagnetic drift modes driven by pressure gradients in tokamaks

A hybrid of hydrodynamics and kinetics is used to study the effect of finite plasma pressure on the pressure-gradient driven toroidal drift modes. The linear drift modes of the system are given by a fifth-order polynomial describing the coupling of the electron-drift, the ion-acoustic, and the shear Alfvén oscillations. The characteristic frequencies, growth rates, and polarization of the electromagnetic modes are investigated as functions of the parameters of toroidicity, plasma gradients, and plasma pressure.

On the nighttime increase of NmF2 at Jicamarca on 2–3 February 1965

The conditions of the nighttime increase in NmF2 at the geomagnetic equator are investigated. It is shown that, in an altitude region above 250 km, after 2100 LT, the increase is due to a downward electromagnetic drift when the compression of the plasma associated with the drift overcomes the chemical loss rate.

A Large Cell Drift Chamber with Image Read Out to Localize High Energy Electromagnetic Showers

The very forward region of the experiment UA1 at the CERN p̄p Collider will be equipped with calorimeters to detect photons and hadrons of energy 5-250 GeV. To localize electromagnetic showers large cell drift chambers will be housed between the modula of the calorimeters.The image of showers will be recorded in two projections by measuring continuously with fast analog to digital converters the drift time and the charge division along the wires.A prototype chamber made up of two 19 cm long drift cells, divided by two rows of 70 cm long anode wires has been built in Rome and tested at CERN with single ionizing particles and showers of energy 5-50 GeV. Results as a function of the shower energy and the ionization rate are reported.

MODEL OF MID-AND LOW-LATITUDE F REGION IONOSPHERE AND PROTONOSPHERE

The coupled continuity and momentum equations of O+ and H+ ions in the F region and the protonosphere are solved for a mid-latitude station (Arecibo) and a low-latitude station (Jicamarca) to investigate the diurnal behavior of the peak electron density NmF2, the height of the peak HmF2, the O+-H+ transition height Htr and the transition level ion density Ntr. The effects of the neutral wind on the NmF2, HmF2 Ntr and Htr curves above Arecibo are more important than and generally in the opposite direction of those of a sinusoidal elctromagnetic drift. the electromagnetic drift plays a fa-reaching role in shaping the ionospheric and protonospheric profiles at Jicamarca. An upward drift that peaks during the day produces a 'valey' in the NmF2 curve, while an upward drift that stays constant during ost of the day produces a 'plateau'. The nighttime decay in Nmf2 is due to the conbined effects of a slow downward drift and chemical recombination. A nocturnal increase in NmF2 is due to a sufficiently large downward drift when the resultant 'squeezing' of the field tubes overcomes the O+ loss rate. The diurnal variations of HmF2 and Htr tend to follow that of the upward drift velocity pattern, with gradients somewhat smoothed. A downward reversal of the drift at sunset causes and enhancement in the post-sunset Ntr.&#x0D; Finally, the applicability of the model to the study of the total electron content measurements of the ATS-6 radio beacon experiments at Ootacamund is demonstrated. By comparing with the observed values, the probable drift velocities over Ootacamund are determined for October and December, 1975. The drift velocity patterns show broad similitarities with those observed over Jicamarca.

Convective cell formation and anomalous diffusion due to electromagnetic drift wave turbulence

Convective cell formation and spectral cascade processes due to gravitational drift Alfvén waves are studied using a new type of model equation. Conservation relations are derived and explosive instability is found for systems near marginal finite β stability. This instability also remains when the effects of poor as well as favorable curvature regions are included, i.e., for ballooning modes. The anomalous diffusion due to convective cells and quasi-linear effects are compared.

A theoretical study of the effects of quiet‐time electromagnetic drifts on the behavior of thermal plasma at mid‐latitudes

Starting with a depleted protonosphere, the behavior of O+ and H+ at L=.2 is examined theoretically to determine the influence of a quiet time diurnal electromagnetic drift with a 24‐hour period. The conditions are appropriate to sunspot maximum. Large changes in the H+ tube content at L=3.2 occur as the protonosphere is replenished. In the absence of the electromagnetic drift, such changes would imply field‐aligned proton fluxes up to the order of 1010 cm−2 s−1; the actual field‐aligned proton flux is of the order of 108 cm−2 s−1. The combined effect of diurnal drifts and frequency of magnetic storms can produce multiple peaks in the diurnal behavior of the H+ tube content at L=3.2. As the drift lowers the altitude of the O+ layer during daytime, the values of NmF2 decrease owing to the change in the linear loss coefficient. At night, cross‐L gradients in NmF2 are significant for the conditions considered, and the outward drift increases NmF2 values at L=3.2. When the protonosphere is sufficiently replenished, the inward drift causes downward proton fluxes at L=3.2.

Seasonal difference in ionization and height of F2-layer caused by neutrals at low latitudes

Simulation of seasonal anomaly based on a morphological study has been carried out for low latitudes. In the morphological study, summer-winter differences have been studied in the diurnal behaviour of foF2, hpF2 and in the strength of the equatorial electrojet for three low-latitude stations and for three different solar activity periods. Simultaneous examination of the equatorial electrojet strength, foF2 and hpF2 show that the seasonal differences cannot be ascribed to the corresponding differences in the magnitude of the electromagnetic drift. Solving the continuity equation at low latitudes for a high solar activity period and assuming increased atomic oxygen in winter (1.15 times) and increased molecular oxygen and nitrogen in summer (1.15 times), it is concluded that the seasonal differences in the calculated foF2 are of the order of the observed seasonal differences (1–1.5 MHz), with the height of the F2-layer showing a trend similar to the observations. Furthermore, the observations from Alouette II as well as the theoretical studies show that seasonal anomaly is dominant only around the F2-peak. Inclusion of a model neutral wind shows that the neutral wind opposes the formation of the seasonal anomaly.

Electromagnetic drift wave turbulence and convective cell formation

A model equation for nonlinear drift Alfvén waves in the region where they do not couple to the electrostatic drift wave branch is derived. Two conservation relations are derived and the results are compared to that of the Hasegawa—Mima equation. The spectrum is found to cascade to both smaller and larger k. The convective cell formation is studied for two different orderings of the parameters. The relation between characteristic scale lengths parallel and perpendicular to the drift flow for the onset of cell formation has been found.