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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Partially Ionized Plasma Physics and Technological Applications

Partially ionized plasma physics has attracted increased attention recently due to numerous technological applications made possible by the increased sophistication of computer modelling, the depth of the theoretical analysis, and the technological applications to a vast field of manufacturing for computer components. Partially ionized plasma is characterized by a significant presence of neutral particles in contrast to the fully ionized plasma. The theoretical analysis is based upon solutions of the kinetic Boltzmann equation, yielding the non-Maxwellian electron energy distribution function (EEDF), thereby emphasizing the difference with a fully ionized plasma. The impact of the effect on discharges in inert and molecular gases is described in detail, yielding the complex nonlinear phenomena resulting in plasma selforganization. A few examples of such phenomena are given, including the non-monotonic EEDFs in the discharge afterglow in a mixture of argon with the molecular gas NF3; the explosive generation of cold electron populations in capacitive discharges, hysteresis of EEDF in inductively coupled plasmas. Recently, highly advanced computer codes were developed in order to address the outstanding challenges in plasma technology. These developments are briefly described in general terms.

non-Maxwellian electron energy distribution functi↗
NASA NTRS1974

The collisional drift mode in a partially ionized plasma

The structure of the drift instability was examined in several density regimes. Let sub e be the total electron mean free path, k sub z the wave-vector component along the magnetic field, and the ratio of perpendicular ion diffusion to parallel electron streaming rates. At low densities (k sub z lambda 1) the drift mode is isothermal and should be treated kineticly. In the finite heat conduction regime square root of m/M k sub z Lambda sub 1) the drift instability threshold is reduced at low densities and increased at high densities as compared to the isothermal threshold. Finally, in the energy transfer limit (k sub z kambda sub e square root of m/M) the drift instability behaves adiabatically in a fully ionized plasma and isothermally in a partially ionized plasma for an ion-neutral to Coulomb collision frequency ratio.

Hudson, M. K.↗
DOE OSTI2024

Kink Instability of Flux Ropes in Partially Ionized Plasmas

In the solar atmosphere, flux ropes are subject to current-driven instabilities that are crucial in driving plasma eruptions, ejections, and heating. A typical ideal magnetohydrodynamics instability developing in flux ropes is the helical kink, which twists the flux rope axis. The growth of this instability can trigger magnetic reconnection, which can explain the formation of chromospheric jets and spicules, but its development has never been investigated in a partially ionized plasma (PIP). Here, we study the kink instability in PIP to understand how it develops in the solar chromosphere, where it is affected by charge-neutral interactions. Partial ionization speeds up the onset of the nonlinear phase of the instability, as the plasma β of the isolated plasma is smaller than the total plasma β of the bulk. The distribution of the released magnetic energy changes in fully ionized plasma and PIP, with a larger increase in internal energy associated with the PIP cases. The temperature in PIP increases faster also due to heating terms from the two-fluid dynamics. PIP effects trigger kink instability on shorter time scales, which is reflected in more explosive chromospheric flux rope dynamics. These results are crucial to understanding the dynamics of small-scale chromospheric structures—minifilament eruptions—that thus far have been largely neglected but could significantly contribute to chromospheric heating and jet formation.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1981

Experimental investigations of turbulence in magnetized, partially ionized plasmas

An experimental investigation of turbulent fluctuations associated with gradient cross-field and Farley-Buneman instabilities is described. The experiments are carried out in magnetized plasma columns with an imposed radial electric field. Microwave scattering and probe measurements provide the plasma diagnostics. Particular attention is given to the varying characteristics of the turbulent spectra for both potential and density as a function of neutral gas pressure.

Mikkelsen, T.↗
NASA NTRS1991

Kinetics and continuum emission of negative atomic ions in partially ionized plasmas

Kinetics and continuum emission of negative ions are studied in stationary atomic hydrogen, nitrogen, and oxygen plasmas. The intensity of the negative-ion emission was found to be neglibible when compared to those of bound-bound and free-bound emission at low and medium particle densities. However, the negative-ion continuum emission can contribute significantly in certain parts of the emission spectrum at high particle densities.

Soon, W. H.↗
NASA NTRS1993

Gravitational instability of a rotating partially-ionized plasma carrying a uniform magnetic field with Hall effect

The problem of gravitational instability of an infinite homogeneous self-gravitating medium carrying a uniform magnetic field in the presence of Hall effect has been investigated to include the effect due to rotation. The dispersion relation has been obtained. It has been found that the Jeans's criterion for the instability remains unaffected even when the effect due to rotation is considered in the presence of Hall effect carrying a uniform magnetic.

Kumar, Vinod↗
NASA NTRS1976

Formation of the 0.511 MeV line in solar flares

The slowing down and annihilation of positrons and the formation of positronium in a solar flare plasma are investigated to determine how the width of the 0.511-MeV line and its strength relative to the three-photon continuum from positronium decay depend on the temperature and density of the medium in which the positron comes to rest. The calculations are limited to the cases of annihilation in a completely ionized plasma, in a partially ionized plasma with an electron/neutron density ratio of 1.0 or 0.1, and in an atomic gas with a very small ion density. Thermally averaged rate coefficients are obtained for the free annihilation of positrons and for positronium formation through radiative recombination in the fully ionized plasma. Positronium formation rates and the resultant energy distributions of the positronium atoms in the partially ionized medium are determined by numerically solving the Fokker-Planck equation in a medium where the ambient free electrons have a Maxwell-Boltzmann distribution of finite temperature but the density of the medium is sufficiently low that positronium atoms decay without further collisions following their formation. A Monte Carlo calculation is performed for the positron energy loss, positronium formation through charge exchange, and positronium breakup in the weakly ionized medium. The energy distributions of decaying positronium atoms and the relative number of triplet to singlet positronium decays are evaluated for ion concentrations and densities characteristic of the solar photosphere.

Crannell, C. J.↗
NASA NTRS2010

Neutral Atom Diffusion in a Partially Ionized Prominence Plasma

The support of solar prominences is normally described in terms of a magnetic force on the prominence plasma that balances the solar gravitational force. Because the prominence plasma is only partially ionized. it is necessary to consider in addition the support of the neutral component of the prominence plasma. This support is accomplished through a frictional interaction between the neutral and ionized components of the plasma, and its efficacy depends strongly on the degree of ionization of the plasma. More specifically, the frictional force is proportional to the relative flow of neutral and ion species, and for a sufficiently weakly ionized plasma, this flow must be relatively large to produce a frictional force that balances gravity. A large relative flow, of course, implies significant draining of neutral particles from the prominence. We evaluate the importance of this draining effect for a hydrogen-helium plasma, and consider the observational evidence for cross-field diffusion of neutral prominence material,

Gilbert, Holly↗
NASA NTRS1974

The electromagnetic interchange mode in a partially ionized collisional plasma

A collisional electromagnetic dispersion relation is derived from two-fluid theory for the interchange mode coupled to the Alfven, acoustic, drift and entropy modes in a partially ionized plasma. The fundamental electromagnetic nature of the interchange model is noted; coupling to the intermediate Alfven mode is strongly stabilizing for finite k sub z. Both ion viscous and ion-neutral stabilization are included, and it was found that collisions destroy the ion finite Larmor radius cutoff at short perpendicular wavelengths.

Hudson, M. K.↗
NASA NTRS2011

Ion-Neutral Coupling in Solar Prominences

Interactions between ions and neutrals in a partially ionized plasma are important throughout heliophysics, including near the solar surface in prominences. Understanding how ion-neutral coupling affects formation, support, structure, and dynamics of prominences will advance our physical understanding of magnetized systems involving a transition from a weakly ionized dense gas to a fully ionized tenuous plasma. We address the fundamental physics of prominence support, which is normally described in terms of a magnetic force on the prominence plasma that balances the solar gravitational force, and the implications for observations. Because the prominence plasma is only partially ionized, it is necessary to consider the support of the both the ionized and neutral components. Support of the neutrals is accomplished through a frictional interaction between the neutral and ionized components of the plasma, and its efficacy depends strongly on the degree of ionization of the plasma. More specifically, the frictional force is proportional to the relative flow of neutral and ion species, and for a sufficiently weakly ionized plasma, this flow must be relatively large to produce a frictional force that balances gravity. A large relative flow, of course, implies significant draining of neutral particles from the prominence. We evaluate the importance of this draining effect for a hydrogen-helium plasma, and consider the observational evidence for cross-field diffusion of neutral prominence material.

Gilbert, Holly↗
DOE OSTI2026

Ionization and temperature measurements in warm dense copper using x-ray absorption spectroscopy

We detail experimental results inferring ionization and temperature for warm dense copper plasmas at several times solid density (15–25 g/cm 3 ) and temperatures of 10–21 eV. Experiments performed at the OMEGA Laser Facility generate uniform warm dense matter conditions via symmetric shock compression of a buried copper layer. The plasma is probed with a laser-generated x-ray source to collect the K-shell x-ray absorption spectrum. Fitting bound-bound absorption contributions from constituent charge states of copper provides an estimated $\overline{Z}$ of approximately 4–7 for these warm dense copper plasmas. We find that these partially ionized plasmas have K-edge shifts of 12–30 eV and bound-bound resonance 1s → 3p absorption shifts of 4–26 eV with respect to the cold K edge. This study provides necessary experimental data to improve ionization and opacity models in the warm dense matter regime.

42 ENGINEERING↗