Sheared flows in near-Earth space plasmas, both magnetic-field-aligned and cross-field, contribute to a rich array of phenomena which can be simulated in the laboratory. This has led to improved knowledge of the basic processes involving velocity shear operative in space, where it is not possible to conduct detailed and repeatable experiments with control over background parameters. Depending upon the flow characteristics, shear can contribute to either growth or damping of various plasma modes or, if sufficiently strong, can itself drive instabilities. These instabilities can have significant consequences in redefining the plasma equilibrium and can lead to energization and transport. A number of laboratory experiments have been performed to investigate the detailed physics associated with inhomogeneous space plasma flows. In this work, a review of in situ observations of processes associated with sheared flows and details of complementary laboratory experimental investigations is presented.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/1998JA900098

Inhomogeneous plasma flows: A review of in situ observations and laboratory experiments

Dust grains in the ring systems and rapidly rotating magnetospheres of the outer planets such as Jupiter and Saturn may be sufficiently charged that the magnetic and electric forces on them are comparable with the gravitational force. The adiabatic theory of charged particle motion has previously been applied to electrons and atomic size particles. But it is also applicable to these charged dust grains in the micrometer and smaller size range. We derive here the guiding center equation of motion, drift velocity, and parallel equation of motion for these grains in a rotating magnetosphere. The effects of periodic grain charge-discharge have not been treated previously and have been included in this analysis. Grain charge is affected by the surrounding plasma properties and by the grain plasma velocity (among other factors), both of which may vary over the gyrocircle. The resulting charge-discharge process at the gyrofrequency destroys the invariance of the magnetic moment and causes a grain to move radially. The magnetic moment may increase or decrease, depending on the gyrophase of the charge variation. If it decreases, the motion is always toward synchronous radius for an equatorial grain. But the orbit becomes circular before the grain reaches synchronous radius, a conclusion that follows from an exact constant of the motion. This circularization can be viewed as a consequence of the gradual reduction in the magnetic moment. This circularization also suggests that dust grains leaving Io could not reach the region of the Jovian ring, but several effects could change that conclusion. Excellent qualitative and quantitative agreement is obtained between adiabatic theory and detailed numerical orbit integrations.

The adiabatic motion of charged dust grains in rotating magnetospheres. [and for ring systems of Jupiter and Saturn

The outer region of the plasma column of a large, linear plasma device is rotated in a controlled fashion by biasing a section of the vacuum chamber wall positive with respect to the cathode (Er<0). The magnitude and temporal dependence of the observed cross-field current, produced when the bias voltage is applied, is consistent with ion current arising from ion-neutral collisions. Flow speeds in the outer regions of the plasma column exceed the local sound speed. In the nonrotating plasma column, cross-field, radial particle transport proceeds at the Bohm diffusion rate. Rotation, above a threshold bias voltage, reduces cross-field transport from Bohm to classical rates, leading to steeper radial density profiles. Reduction of particle transport is global and not isolated to the region of flow shear. The transition from the nonrotating to the rotating plasma edge in the linear plasma column is similar to the low confinement to high confinement mode transition observed in tokamaks when Er<0.

Transition from Bohm to classical diffusion due to edge rotation of a cylindrical plasma

A model for the collisionless plasma-wall problem under the action of an applied magnetic field is developed. The behavior of its solution is examined and found to be qualitatively consistent with experiment. The plasma and the sheath are then modeled separately to obtain the position of the quasi-neutral plasma boundary and the position of the edge of the electron-free sheath. It is shown that the plasma boundary can be specified as the point where the component of the ion velocity normal to the wall reaches the ion sound speed (Bohm criterion), and the sheath edge is specified as the point corresponding to Godyak's condition for the electric field. Studying the behavior near the plasma boundary and the sheath edge, the plasma solution and the solution of the space charge region are patched together to approximate the solution of the plasma-wall problem.

Plasma-sheath transition in the magnetized plasma-wall problem for collisionless ions

Thank you for downloading an introduction to classical electromagnetic radiation. Maybe you have knowledge that, people have look numerous times for their favorite novels like this an introduction to classical electromagnetic radiation, but end up in malicious downloads. Rather than enjoying a good book with a cup of coffee in the afternoon, instead they are facing with some malicious virus inside their laptop.

An Introduction To Classical Electromagnetic Radiation

RF confined electron plasmas are of importance in Paul traps [W. Paul, Rev. Mod. Phys. 62, 531 (1990)]. The stability of such plasmas is unclear and statistical heating arguments have been advanced to explain the observed heating in such plasmas [I. Siemers et al., Phys. Rev. A 38, 5121 (1988)]. This study investigates the nature of a one-dimensional collisionless electron plasma that is confined by an rf field of the form [−B+Acos(ωt)]x, where x is the space coordinate and ω is the rf frequency. Nonlinearly exact solutions are obtained. The distribution function and the plasma density are obtained in closed form and have constant shapes with time varying oscillations. These oscillations are at the rf frequency and its harmonics, modulated by a low frequency related to the electron bounce time. The linear limit of weak fields is recovered. Analytic expressions are obtained for the required external field to make it consistent with prescribed distribution functions. These solutions remain valid even in the...

Analytic, nonlinearly exact solutions for an rf confined plasma

Exact solutions for one-dimensional (1D) plasma dynamics in an rf trap are known when space charge effects are neglected [K. Shah and H. S. Ramachandran, Phys. Plasmas 15, 062303 (2008)]. In this work, weak space charge effects in an rf trap are considered. An analytic expression for the time varying distribution function of the 1D plasma is obtained. It is shown that the plasma is a Maxwellian up to the lowest order in nonlinearity and that the spatially constant temperature periodically oscillates in time at the same rate as the rf frequency. It was shown by Krapchev [Phys. Rev. Lett. 42, 497 (1979)] that the time averaged distribution function is double humped with respect to velocity beyond a certain threshold in space. The time average of the complete time varying distribution function is obtained and some of the predictions of Krapchev are recovered, while also finding discrepancies. The relationship between stroboscopic orbits and the time averaged ponderomotive orbit are obtained for such traps.

Space charge effects in rf traps: Ponderomotive concept and stroboscopic analysis

This paper describes the design, development and test results of the Electrical Power Subsystem (EPS) of IITMSAT — the nano-satellite project of Indian Institute of Technology Madras (IITM). IITMSAT's payload comprises of an indigenously designed and developed Space based Proton Electron Energy Detector (SPEED). It is designed to measure the high energy particle precipitations just below the Van Allen Belts. Apart from SPEED, the satellite electronics include the health monitoring sensors, attitude sensors, three 32-bit ARM microcontrollers to process the data, communication module, Beacon, Command and Data Management System (CDMS) and electromagnetic actuators (Torque Rods) to align the satellite along the Earth's local magnetic field in the Low Earth Orbit (LEO). This indigenous EPS was designed and developed using low-cost, high-performance commercial off-the-shelf (COTS) components of industrial grade, to power loads of about 6 Watts. This paper describes the satellite power requirements, EPS hardware design, simulation results followed by practical results obtained from the prototype hardware.

Design of Electrical Power Subsystem for IITMSAT

Far-field patterns of wire antennas on a PEC sphere are calculated from quasi-static near fields using spherical harmonic expansion. Three cases of the wire antennas—F-antenna, dipole, and resonant loop on the PEC sphere—are considered. With the assumed sinusoidal current distribution on the antenna, the method of images is employed to obtain currents and charges on the antenna's image against the sphere. Only from the charge density and current distributions of the wire antenna and its image, ignoring the sphere, the quasi-static near fields are calculated using Coulomb's and Biot–Savart's laws. The fields in a source-free region are expressed in spherical harmonic expansion with the coefficients obtained from the radial components of the calculated quasi-static electric and magnetic near fields. The far fields thus obtained from the expansion match well with that of the simulated patterns. Deviations between simulation and theory are discussed and explained.

Determination of Far Fields of Wire Antennas on a PEC Sphere Using Spherical Harmonic Expansion

A one-dimensional plasma discharge is analyzed under steady state conditions. Using simple models for source and collisions, a first-order differential equation is obtained that simultaneously describes both the bulk and the presheath of the plasma. This equation is numerically solved in various regimes and physically interesting quantities such as the ratio of bulk to edge density and the size of the inertial terms in the bulk region are presented. Analytic expressions are obtained for profiles when collision frequency is assumed constant. Findings include nB/nSE∼2.5 for highly collisional systems, significant flow in the bulk plasma, and modified I–V characteristics.

Harishankar Ramachandran

Papers

Analytic, nonlinearly exact solutions for an rf confined plasma

Space charge effects in rf traps: Ponderomotive concept and stroboscopic analysis

Design of Electrical Power Subsystem for IITMSAT

Determination of Far Fields of Wire Antennas on a PEC Sphere Using Spherical Harmonic Expansion

A self-consistent analysis of a collisional presheath