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NASA NTRS2003

Numerical Simulation of Waves Driven by Plasma Currents Generated by Low-Frequency Alfven Waves in a Multi-Ion Plasma

When multi-ion plasma consisting of heavy and light ions is permeated by a lowfrequency Alfien (LFA) wave, the EXB and the polarization drifts of the different ion species and the electrons could be quite different. The relative drifts between the charged-particle species drive waves, which energize the plasma. Using 2.5-D particle-in-cell simulations, we study this process of wave generation and its nonlinear consequences in terms of acceleration and heating plasma. Specifically we study the situation for LFA wave frequency being lower than the heavyion cyclotron frequency in a multi-ion plasma. We impose such a wave to the plasma assuming that its wavelength is much larger than that of the waves generated by the relative drifts. For better understanding, the LFA-wave driven simulations are augmented by those driven by initialized ion beams.

Singh, Nagendra↗

NASA NTRS2004

Numerical Simulation of Waves Driven by Plasma Currents Generated by Low-Frequency Alfven Waves in a Multi-Ion Plasma

When multi-ion plasma consisting of heavy and light ions is permeated by a low-frequency Alfven (LFA) wave, the crossed-electric-and-magnetic field (E x B), and the polarization drifts of the different ion species and the electrons could be quite different. The relative drifts between the charged-particle species drive waves, which energize the plasma. Using 2.5-dimensional (2.5-D) particle-in-cell simulations, we study this process of wave generation and its nonlinear consequences in terms of acceleration and heating plasma. Specifically, we study the situation for LFA wave frequency being lower than the heavy-ion cyclotron frequency in a multi-ion plasma. We impose such a wave to the plasma assuming that its wavelength is much larger than that of the waves generated by the relative drifts. For better understanding, the LFA-wave driven simulations are augmented by those driven by initialized ion beams. The driven high-frequency (HF) wave modes critically depend on the heavy ion density nh; for small values of nh, the lower hybrid (LH) waves dominate. On the other hand, for large nh a significantly enhanced level of waves occurs over a much broader frequency spectrum below the LH frequency and such waves are interpreted here as the ion Bernstein (IB) mode near the light ion cyclotron harmonics. Irrespective of the driven wave modes, both the light and heavy ions undergo significant transverse acceleration, but for the large heavy-ion densities, even the electrons are significantly accelerated in the parallel direction by the waves below the LH frequency. Even when the LFA wave drive is maintained, the ion heating leads to the cessation of HF wave excitation just after a few cycles of the former wave. On the basis of marginal stability seen in the simulations, an empirical relation for LFA wave amplitude, frequency and ion temperature is given.

Singh, Nagendra↗

NASA NTRS1982

Finite amplitude Alfven waves in a multi-ion plasma - Propagation, acceleration, and heating

An expression is derived for the wave action flux of finite-amplitude Alfven waves in a multi-ion plasma. The expression is valid in the presence of dissipative forces and permits an arbitrary angle between the average magnetic field and the wave vector. Applying the conservation of wave action and the first law of thermodynamics yields, for a multi-ion plasma, an expression for the spatial evolution of Alfven wave amplitude in the absence of dissipation. It also gives the relationship between the wave amplitude and the dissipative heating, as well as an expression for the acceleration of an ion species by finite-amplitude Alfven waves. It is pointed out that the acceleration comprises a nondissipative wave pressure that is identical to that derived previously under more restrictive conditions and a new term giving the acceleration that must accompany dissipative heating. The results are discussed in the context of the observations of heavy ions in the solar wind.

Isenberg, P. A.↗

NASA NTRS1996

Fundamental processes in the expansion, energization, and coupling of single- and multi-Ion plasmas in space: Laboratory simulation experiments

We have conducted a laboratory investigation into the physics of plasma expansions and their associated energization processes. We studied single- and multi-ion plasma processes in self-expansions, and included light and heavy ions and heavy/light mixtures to encompass the phenomenological regimes of the solar and polar winds and the AMPTE and CRRES chemical release programs. The laboratory experiments provided spatially-distributed time-dependent measurements of total plasma density, temperature, and density fluctuation power spectra with the data confirming the long-theorized electron energization process in an expanding cloud - a result that was impossible to determine in spaceborne experiments (as e.g., in the CRRES program). These results provided the missing link in previous laboratory and spaceborne programs. confirming important elements in our understanding of such solar-terrestrial processes as manifested in expanding plasmas in the solar wind (e.g., CMES) and in ionospheric outflow in plasmaspheric fluctuate refilling after a storm. The energization signatures were seen in an entire series of runs that varied the ion species (Ar', Xe', Kr' and Ne'), and correlative studies included spectral analyses of electrostatic waves collocated with the energized electron distributions. In all cases wave energies were most intense during the times in which the suprathermal populations were present, with wave intensity increasing with the intensity of the suprathermal electron population. This is consistent with theoretical expectations wherein the energization process is directly attributable to wave particle interactions. No resonance conditions were observed, in an overall framework in which the general wave characteristics were broadband with power decreasing with increasing frequency.

Szuszczewicz, E. P.↗

NASA NTRS1971

Ion acoustic waves in a multi-ion plasma.

An exact treatment of the multispecies ion acoustic dispersion relation is given for an argon/helium plasma. Phase velocity and damping are obtained as a function of ion-electron temperature ratio and relative densities of the two species. There are two important modes in the plasma, with quite different phase velocities, which are referred to as principal heavy ion mode and principal light ion mode. Which of these is dominant depends on the relative densities of the two components, but, in general, the light ion mode becomes important for surprisingly small light ion contamination. Approximate analytic expressions are derived from damping rates and phase velocities and their domains of validity are investigated. Relevance of the results for the investigation of collisionless shocks is discussed.

Fried, B. D.↗

NASA NTRS1983

Expansion of a multi-ion plasma into a vacuum

A numerical investigation of the expansion of a plasma with two ion species into a vacuum is presented. A set of Vlasov equations describe the ion behavior and the electrostatic potential is modelled by the Poisson equation. Electrons are assumed to follow Boltzmann's law. A plasma with H(+) and O(+) ions is considered, with the ions forming various combinations. Hydrodynamic calculations are performed for ions and electrons at equal temperatures, and for the presence of hot electrons. Self-similarity is shown to be valid where charge neutrality is dominant. An absence of significant quantities of ion-acoustic oscillations were observed.

Singh, N.↗

NASA NTRS2003

The Nonlinear Coupling of Alfven and Lower Hybrid Waves in Space Plasma

Khazanov, G. V.↗

NASA NTRS2003

The Nonlinear Coupling of Electromagnetic Ion Cyclotron and Lower Hybrid Waves in the Ring Current Region: The Magnetic Storm May 1-7 1998

The excitation of lower hybrid waves (LHWs) is a widely discussed mechanism of interaction between plasma species in space, and is one of the unresolved questions of magnetospheric multi-ion plasmas. In this paper we present the morphology, dynamics, and level of LHW activity generated by electromagnetic ion cyclotron (EMIC) waves during the May 2-7, 1998 storm period on the global scale. The LHWs were calculated based on our newly developed self-consistent model that couples the system of two kinetic equations: one equation describes the ring current (RC) ion dynamic, and another equation describes the evolution of EMIC waves. It is found that the LHWs are excited by helium ions due to their mass dependent drift in the electric field of EMIC waves. The level of LHW activity is calculated assuming that the induced scattering process is the main saturation mechanism for these waves. The calculated LHWs electric fields are consistent with the observational data.

Khazanov, G. V.↗

NASA NTRS2004

The Nonlinear Coupling of Alfven and Lower Hybrid Waves in Space Plasma

Space plasmas support a wide variety of waves, and wave-particle interactions as well as wave-wave interactions which are of crucial importance to magnetospheric and ionospheric plasma behavior. The excitation of lower hybrid waves (LHWs) in particular is a widely discussed mechanism of interaction between plasma species in space and is one of the unresolved questions of magnetospheric multi-ion plasmas. It is demonstrated that large-amplitude Alfven waves may generate LHWs in the auroral zone and ring current region and in some cases (particularly in the inner magnetosphere) this serves as the Alfven wave saturation mechanism. We present several examples of observational data which illustrate that the proposed mechanism is a plausible candidate to explain certain classes of LHW generation events in the ionosphere and magnetosphere and demonstrate electron and ion energization involving these processes. We discuss the morphology dynamics and level of LHW activity generated by electromagnetic ion cyclotron (EMIC) waves during the May 2-7 1998 storm period on the global scale. The LHWs were calculated based on a newly developed self-consistent model (Khazanov et. al. 2002) that couples the system of two kinetic equations: one equation describes the ring current (RC) ion dynamic and another equation describes the evolution of EMIC waves. It is found that the LHWs are excited by helium ions due to their mass dependent drift in the electric field of EMIC waves. The level of LHW activity is calculated assuming that the induced scattering process is the main saturation mechanism for these waves. The calculated LHWs electric fields are consistent with the observational data.

Khazanov, George V.↗

NASA NTRS1977

Time-resolved double-probe study in a He-Hg afterglow plasma

An experimental double-probe technique is described which allows the He(+) ion density to be measured directly as a function of time in the afterglow of a helium-metal-vapor discharge. As an application example, two CW laser transitions of the He-Hg(+) laser at 6150 and 7944 A are considered which both arise from excited 7p (2) P terms of Hg II. The time-resolved double-probe technique is used to measure the destruction rate of the He(+) ion density, which is then compared with the spontaneous-emission decay rate for 7p (2) P terms of Hg II. The results obtained show unambiguously and directly that the dominant excitation process for the two transitions considered is a charge-transfer collisional reaction of the form He(+) plus Hg yields He plus metastable Hg(+) plus the energy defect for this reaction. It is noted that the time-resolved double-probe technique may provide a simple method for measuring ion mobilities in a multi-ion plasma.

Shay, T.↗

NASA NTRS1982

Multi-ion resonances in finite temperature plasma

Dispersion properties of electrostatic waves in a multi-ion plasma are examined, with an analysis that incorporates the effects of finite temperature, finite parallel wavenumber, and wave growth/damping in a systematic development of equations. Numerical solutions and analytic formulas are given for an ion plasma consisting of H(+), O(+), and S(+) for application to Jupiter's magnetosphere. It is demonstrated how observations of plasma resonance lines may be used as a diagnostic of ion composition in magnetospheric plasma. This potential use of high-sensitivity/high-resolution plasma wave instrumentation may provide information necessary to resolve issues concerning the origin of plasmas in the earth's neighborhood.

Barbosa, D. D.↗

NASA NTRS2003

Self-Consistent Model of Magnetospheric Ring Current and Electromagnetic Ion Cyclotron Waves: The May 2-7, 1998, Storm

Complete description of a self-consistent model for magnetospheric ring current interacting with electromagnetic ion cyclotron waves is presented. The model is based on the system of two kinetic equations; one equation describes the ring current ion dynamics, and another equation describes the wave evolution. The effects on ring current ions interacting with electromagnetic ion cyclotron waves, and back on waves, are considered self-consistently by solving both equations on a global magnetospheric scale under non steady-state conditions. In the paper by Khazanov et al. [2002] this self-consistent model has only been shortly outlined, and discussions of many the model related details have been omitted. For example, in present study for the first time a new algorithm for numerical finding of the resonant numbers for quasilinear wave-particle interaction is described, or it is demonstrated that in order to describe quasilinear interaction in a multi-ion thermal plasma correctly, both e and He(+) modes of electromagnetic ion cyclotron waves should be employed. The developed model is used to simulate the entire May 2-7, 1998 storm period. Trapped number fluxes of the ring current protons are calculated and presented along with their comparison with the data measured by the 3D hot plasma instrument Polar/HYDRA. Examining of the wave (MLT, L shell) distributions produced during the storm progress reveals an essential intensification of the wave emissions in about two days after main phase of storm. This result is well consistent with the earlier ground-based observations. Also the theoretical shapes and the occurrence rates for power spectral densities of electromagnetic ion cyclotron waves are studied. It is found that in about 2 days after the storm main phase on May 4, mainly non Gaussian shapes of power spectral densities are produced.

Khazanov, G. V.↗

NASA NTRS1995

Analytical model for the density distribution in the Io plasma torus

An analytical model is developed for the diffusive equilibrium plasma density distribution in the Io plasma torus. The model has been employed successfully to follow the ray path of plasma waves in the multi-ion Jovian magnetosphere; it would also be valuable for other studies of the Io torus that require a smooth and continuous description of the plasma density and its gradients. Validity of the analytical treatment requires that the temperature of thermal electrons be much lower than the ion temperature and that superthermal electrons be much less abundant than the thermal electrons; these two conditions are satisfied in the warm outer region of the Io torus from L = 6 to L = 10. The analytical solutions agree well with exact numerical calculations for the most dense portion of the Io torus within 30 deg of the equator.

Mei, YI↗

NASA NTRS1984

Resonant acceleration and heating of solar wind ions Anisotropy and dispersion

This paper is an extension of recent work by Isenberg and Hollweg dealing with the preferential acceleration and heating of solar wind heavy ions by a resonant cyclotron interaction with a turbulent spectrum of ion-cyclotron waves. Two major approximations of the previous work are eliminated: that of isotropic ion distributions, and that of nondispersive waves. The wave action flux of finite-amplitude Alfven waves in a multi-ion, differentially flowing, gyrotropic plasma is derived. This quantity is incorporated into the wave-driven solar wind model of Isenberg and Hollweg, which is then applied to gyrotropic protons and alpha particles. It is found that allowing for nonisotropic ions yields enhanced preferential acceleration of alpha particles. However, when dispersion is included in the resonant interaction, the preferential effects are again reduced. These more realistic calculations show that the observations of solar wind alpha particles cannot be explained by a resonant cyclotron interaction.

Isenberg, P. A.↗

NASA NTRS1996

A proof of concept investigation: A unique mobility spectrometer for In Situ diagnostics of positive and negative ion distributions in the mesosphere and lower ionosphere

We have carried out a proof-of-concept development and test effort that not only promises the reduction of parasitic effects of surface contamination (therefore increasing the integrity of 'in situ' measurements in the 60-130 km regime), but promises a uniquely expanded measurement set that includes electron densities, plasma conductivities, charged-particle mobilities, and mass discrimination of positive and negative ion distributions throughout the continuum to free-molecular-flow regimes. Three different sensor configurations were designed, built and tested, along with specialized driving voltage, electrometer and channeltron control electronics. The individual systems were tested in a variety of simulated space environments ranging from pressures near the continuum limit of 100 mTorr to the collisionless regime at 10(exp -6) Torr. Swept modes were initially employed to better understand ion optics and ion 'beam' losses to end walls and to control electrodes. This swept mode also helped better understand and mitigate the influences of secondary electrons on the overall performance of the PIMS design concept. Final results demonstrated the utility of the concept in dominant single-ion plasma environments. Accumulated information, including theoretical concepts and laboratory data, suggest that multi-ion diagnostics are fully within the instrument capabilities and that cold plasma tests with minimized pre-aperture sheath acceleration are the key ingredients to multi-ion success.

Szuszczewicz, Edward P.↗

NASA NTRS1994

Shock normal determination for multiple-ion shocks

We have adapted the single-ion Vinas and Scudder (1986) solution to the Rankine-Hugoniot (R-H) problem to a multiple-on solution. Using this technique, we can calculate a shock normal direction, shock speed, best estimate of the upstream and downstream magnetic field and plasma asymptotic states, and theta(sub Bn), the angle between the shock normal and the upstream magnetic field. We test the multi-ion solution with a theoretical case but are restricted to a perpendicular shock in order to close the multi-ion Rankine-Hugoniot equations. For this test case both single-ion and multi-ion solutions are equally valid. We examine parameter regimes to look for differences between single-ion and multi-ion solutions of the R-H equations, and we find that the largest differences occur for quasi-parallel shocks, small values of solar wind speed, large values of heavy ion density, and very strong and very weak shocks. For both the inbound and outbound crossing of comet Halley we have a slow solar wind speed, small values of water group ions and fairly weak shocks. We examine both the quasi-perpendicular inbound crossing and the quasi-parallel outbound crossing at comet Halley.

Kessel, R. L.↗

NASA NTRS1994

A multi-ion generalized transport model of the polar wind

The higher-order generalizations of the equations of standard hydrodynamics, known collectively as generalized transport theories, have been used since the early 1980s to describe the terrestrial polar wind. Inherent in the structure of generalized transport theories is the ability to describe not only interparticle collisions but also certain non-Maxwellian processes, such as heat flow and viscous stress, that are characteristic of any plasma flow that is not collision dominated. Because the polar wind exhibits a transition from collision-dominated to collisionless flow, generalized transport theories possess advantages for polar wind modeling not shared by either collision-dominated models (such as standard hydrodynamics) or collisionless models (such as those based on solving the collisionless Boltzmann equation). In general, previous polar wind models have used generalized transport equations to describe electrons and only one species of ion (H(+)). If other ion species were included in the models at all, it was in a simplified or semiempirical manner. The model described in this paper is the first polar wind model that uses a generalized transport theory (bi-Maxwellian-based 16-moment theory) to describe all of the species, both major and minor, in the polar wind plasma. In the model, electrons and three ion species (H(+), He(+), O(+)) are assumed to be major and several ion species are assumed to be minor (NO(+), Fe(+), O(++)). For all species, a complete 16-moment transport formulation is used, so that profiles of density, drift velocity, parallel and perpendicular temperatures, and the field-aligned parallel and perpendicular energy flows are obtained. In the results presented here, emphasis is placed on describing those constituents of the polar wind that have received little attention in past studies. In particular, characteristic solutions are presented for supersonic H(+) outflow and for both supersonic and subsonic outflows of the major ion He(+). Solutions are also presented for various minor ions, both atomic and molecular and both singly and multiply charged.

Demars, H. G.↗

NASA NTRS1993

The multi-ion, multi-event test of ion cyclotron resonance heating

The multi-ion, multi-event study of ion cyclotron resonance heating was funded to study ion energization through ion cyclotron resonance with low frequency broadband electromagnetic turbulence. The initial work on the ion cyclotron resonance heating (ICRH) of oxygen ions was presented in Crew et al. Crew and his co-authors developed a two-parameter representation of selected oxygen conic distributions and modeled the conic formation in terms of resonance heating. The first year seeks to extend the work of Crew and his co-authors by testing the applicability of the ICRH mechanism to helium ion conic distributions, using data obtained from the Energetic Ion Composition Spectrometer and the Plasma Wave Instrument on Dynamics Explorer 1.

Persoon, Ann M.↗