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Results for “PLASMA EXPANSION”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Investigation of shock-shock interaction and Mach reflection in laterally colliding laser-blow-off plasmas

Interactions of two Li plasma plumes and shock waves are investigated at various pressures (∼10{sup −5} to 3 mbar) in the argon gas ambient. Fast imaging and optical emission spectroscopy are used to study the plume dynamics and characteristic emission of plasmas. The plasma plumes are created in laser-blow-off geometry. The expansion of plasma plumes in the ambient gas leads to the formation of an interaction zone. The formation of interaction zone is dependent on the ambient pressure and below a certain pressure, no significant change is observed in the shape and size of the interaction plasma. In the higher pressure, formation of interaction zone and its shape are dependent on ambient pressure. Dynamics of seed plasmas and interaction zone are also affected by the shock-shock interactions. The shock-shock interaction depends on the angle of incidence (α) between two shock waves at the initial time of interaction but as the plumes expand, the shock-shock interaction does not follow α dependence.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Coulomb expansion of a thin dust cloud observed experimentally under afterglow plasma conditions

The Coulomb expansion of a thin cloud of charged dust particles was observed experimentally, in a plasma afterglow. This expansion occurs due to mutual repulsion among positively charged dust particles, after electrons and ions have escaped the chamber volume. In the experiment, a two-dimensional cloud of dust particles was initially levitated in a glow-discharge plasma. The power was then switched off to produce afterglow conditions. The subsequent fall of the dust cloud was slowed by reversing the electric force, to an upward direction, allowing an extended observation. At early time, measurements of the Coulomb expansion in the horizontal direction are found to be accurately modeled by the equation of state for a uniformly charged thin disk. Finally, bouncing from the lower electrode was found to be avoided by lowering the impact velocity <100 mm/s.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Study of the expansion dynamics of the plasma of a thin aluminum foil under the action of soft X-ray emission

Results are presented from experiments on the irradiation of thin aluminum foils by an intense soft X-ray (SXR) source on the basis of the Z-pinch formed during the implosion of a tungsten wire array at the Angara-5-1 facility. The state of the foil target is examined by taking two-dimensional X-ray frames. The expansion velocity of the plasma formed under the action of pulsed SXR emission on the front (irradiated) and back sides of the foil and the glow intensity of aluminum plasma on the back side are found from the spatial distribution of the radiation intensity of the plasma of the irradiated foil. The time at which the foil plasma becomes transparent to Z-pinch radiation is determined from the increase in the intensity of transmitted SXR emission.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Investigating the dynamics of laser induced sparks in atmospheric helium using Rayleigh and Thomson scattering

We have used optical Rayleigh and Thomson scattering to investigate the expansion dynamics of laser induced plasma in atmospheric helium and to map its electron parameters both in time and space. The plasma is created using 9 ns duration, 140 mJ pulses from a Nd:YAG laser operating at 1064 nm, focused with a 10 cm focal length lens, and probed with 7 ns, 80 mJ, and 532 nm Nd:YAG laser pulses. Between 0.4 μs and 22.5 μs after breakdown, the electron density decreases from 3.3 × 10{sup 17 }cm{sup −3} to 9 × 10{sup 13 }cm{sup −3}, while the temperature drops from 3.2 eV to 0.1 eV. Spatially resolved Thomson scattering data recorded up to 17.5 μs reveal that during this time the laser induced plasma expands at a rate given by R ∼ t{sup 0.4} consistent with a non-radiative spherical blast wave. This data also indicate the development of a toroidal structure in the lateral profile of both electron temperature and density. Rayleigh scattering data show that the gas density decreases in the center of the expanding plasma with a central scattering peak reemerging after about 12 μs. We have utilized a zero dimensional kinetic global model to identify the dominant particle species versus delay time and this indicates that metastable helium and the He{sub 2}{sup +} molecular ion play an important role.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Control of laser-ablation plasma potential with external electrodes

The potential of a laser-ablation plasma was controlled stably up to +2 kV by using external ring electrodes. A stable electron sheath was formed between the plasma and the external electrodes by placing the ring electrodes away from the boundary of the drifting plasma. The plasma kept the potential for a few μs regardless of the flux change of the ablation plasma. We also found that the plasma potential changed with the expansion angle of the plasma from the target. By changing the distance between the plasma boundary and the external electrodes, we succeeded in controlling the potential of laser-ablation plasma.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1986

Plasma waves associated with the first AMPTE magnetotail barium release

Plasma waves observed during the March 21, 1985, AMPTE magnetotail barium release are described. Electron plasma oscillations provided local measurements of the plasma density during both the expansion and decay phases. Immediately after the explosion, the electron density reached a peak of about 400,000/cu cm, and then started decreasing approximately as t to the -2.4 as the cloud expanded. About 6 minutes after the explosion, the electron density suddenly began to increase, reached a secondary peak of about 240/cu cm, and then slowly decayed down to the preevent level over a period of about 15 minutes. The density increase is believed to be caused by the collapse of the ion cloud into the diamagnetic cavity created by the initial expansion. The plasma wave intensities observed during the entire event were quite low. In the diamagnetic cavity, electrostatic emissions were observed near the barium ion plasma frequency, and in another band at lower frequencies. A broadband burst of electrostatic noise was also observed at the boundary of the diamagnetic cavity. Except for electron plasma oscillations, no significant wave activity was observed outside of the diamagnetic cavity.

Gurnett, D. A.↗
DOE OSTI2016

Plasma heating via adiabatic magnetic compression-expansion cycle

Heating of collisionless plasmas in closed adiabatic magnetic cycle comprising of a quasi static compression followed by a non quasi static constrained expansion against a constant external pressure is proposed. Thermodynamic constraints are derived to show that the plasma always gains heat in cycles having at least one non quasi static process. The turbulent relaxation of the plasma to the equilibrium state at the end of the non quasi static expansion is discussed and verified via 1D Particle in Cell (PIC) simulations. Applications of this scheme to heating plasmas in open configurations (mirror machines) and closed configurations (tokamak, reverse field pinche) are discussed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Energy conversion and transfer for plasmas in a magnetic expansion configuration

A two-dimensional axisymmetric particle-in-cell code with Monte Carlo collision conditions has been used to study particle energy transfer in plasmas and conversion in applied magnetic and electric fields appropriate to coaxial acceleration. The research incorporates a computation scheme with: a model of single particle magnetic interactions; a model of single particle interactions in electric and magnetic fields; and a model of multi-particle collisional interactions in order to understand the energy transfer processes and conversion mechanisms of charged plasma particles. This approach predicts electron and ion motions along with their energy variations for physical conditions that occur in the related models; the results allow comparison with experimental data for magnetic field strengths of 0.01–0.05 T and electrode voltages of 22.0–32.0 V. With the incorporation of magnetic and electric field effects on charged particles, the multi-particle model includes electron-neutral ionization collisions, ion-neutral charge exchange collisions, and electron-ion Coulomb collisions. This research presents a new approach to achieve an underlying understanding of the plasma energy transfer and conversion in the external electric and magnetic fields that is not possible using magnetohydrodynamics continuum representations. Results indicate the following innovative conclusions: (1) Radial and azimuthal energies of magnetized electrons are converted into an axial electron energy component in the diverging magnetic field, and the azimuthal kinetic energy of unmagnetized ions is converted into axial and radial components. (2) In electric and magnetic fields, electric field energy is primarily converted into axial kinetic energy of magnetized electrons by the energy transformation effects of magnetic fields, and for unmagnetized ions, the radial kinetic energy component dominates in the conversion of electric field energy. (3) For the collisional plasma, electron kinetic energy tends to increase (or decrease) to a terminal value since electrons lose energy in collisions then gain energy again from the field. Ions acquire most energy directly from the electric field, although part of the electric field energy arrives to the ions by collisions. Further, the ion axial energy component dominates the total ion energy. The collision processes are found to be integral and essential for the conversion of the plasma non-directed energy gain to be converted into the resultant axial energy, the magnitudes of which are found to be in agreement with experimental results.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Particle-in-cell simulation study of a lower-hybrid shock

The expansion of a magnetized high-pressure plasma into a low-pressure ambient medium is examined with particle-in-cell simulations. The magnetic field points perpendicular to the plasma's expansion direction and binary collisions between particles are absent. The expanding plasma steepens into a quasi-electrostatic shock that is sustained by the lower-hybrid (LH) wave. The ambipolar electric field points in the expansion direction and it induces together with the background magnetic field a fast E cross B drift of electrons. The drifting electrons modify the background magnetic field, resulting in its pile-up by the LH shock. The magnetic pressure gradient force accelerates the ambient ions ahead of the LH shock, reducing the relative velocity between the ambient plasma and the LH shock to about the phase speed of the shocked LH wave, transforming the LH shock into a nonlinear LH wave. The oscillations of the electrostatic potential have a larger amplitude and wavelength in the magnetized plasma than in an unmagnetized one with otherwise identical conditions. The energy loss to the drifting electrons leads to a noticeable slowdown of the LH shock compared to that in an unmagnetized plasma.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Radial acceleration of ions during adiabatic expansion of a multicomponent cylindrical plasma

The methods of modern group analysis allow an analytic solution of the Cauchy problem to be constructed for the system of kinetic equations for a fully ionised electron – ion plasma, describing the acceleration of ions during the adiabatic expansion of a cylindrical plasma. Time and spatial dependences of the distribution functions of particles are obtained and their integral characteristics, such as density, average velocity, temperature, and energy spectrum, are found. The formation of the energy spectrum of accelerated ions, asymptotically repeating the spatial distribution of their density, and the cooling of electrons in the process of ion acceleration are analytically described. Particular attention is paid to the investigation of the influence of the heavy ionic component on the dynamics of the light component. The features of ion acceleration in the case of a two-temperature electron distribution function that describes the presence of hot and cold electron components are studied, which corresponds to the typical conditions of the experiment on plasma heating by intense laser radiation. (paper)

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1992

The stability of the near-Earth magnetotail against the ballooning instability

In an extension to a previous study, conditions for the ballooning instability in the magnetohydrodynamic approximation are derived. It is necessary for exciting the ballooning instability that the plasma pressure is higher where plasma is convected outward. However, the expansion of plasma, which results from the divergence of outward flows in the curved geometry of field lines, may overcompensate for the convective change in the plasma pressure. Conditions for the instability are derived from the equation describing the linear coupling between the Alfven and slow magnetosonic waves. The result indicates that excessive curvature stabilizes, rather than destabilizes, perturbations, as well as the field aligned current and the field aligned flow. That is the field line curvature should be smaller than the pressure gradient for exciting the ballooning instability. It is inferred that this condition is not satisfied during quiet times in the near Earth tail. The plasma sheet becomes more stable to the instability in accordance with the thinning of the plasma sheets during the growth phase of substorms, while in the region nearer to the Earth (the inner edge of the plasma sheet or the ring current region) the plasma pressure gradient, which is possibly localized during the growth phase, may drive the instability.

Ohtani, Shin-Ichi↗
DOE OSTI2019

Laser-generated plasmas in length scales relevant for thin film growth and processing: simulation and experiment

In pulsed laser deposition, thin film growth is mediated by a laser-generated plasma, whose properties are critical for controlling the film microstructure. The advent of 2D materials has renewed the interest in how this ablation plasma can be used to manipulate the growth and processing of atomically thin systems. For such purpose, a quantitative understanding of the density, charge state, and kinetic energy of plasma constituents is needed at the location where they contribute to materials processes. Here, we study laser-induced plasmas over expansion distances of several centimeters from the ablation target, which is the relevant length scale for materials growth and modification. The study is enabled by a fast implementation of a laser ablation/plasma expansion model using an adaptive Cartesian mesh solver. Simulation outcomes for KrF excimer laser ablation of Cu are compared with Langmuir probe and optical emission spectroscopy measurements. Furthermore, simulation predictions for the plasma-shielding threshold, the ionization state of species in the plasma, and the kinetic energy of ions, are in good correspondence with experimental data. For laser fluences of 1–4 J cm -2 , the plume is dominated by Cu 0 , with small concentrations of Cu+ and electrons at the expansion front. Higher laser fluences (e.g. 7 J cm -2 ) lead to a Cu + -rich plasma, with a fully ionized leading edge where Cu 2+ is the dominant species. In both regimes, simulations indicate the presence of a low-density, high-temperature plasma expansion front with a high degree of ionization that may play a significant role in doping, annealing, and kinetically-driven phase transformations in 2D materials.

2D materials↗
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 NTRS1992

Interaction between alpha 2-adrenergic and angiotensin II systems in the control of glomerular hemodynamics as assessed by renal micropuncture in the rat

The hypothesis that renal alpha 2 adrenoceptors influence nephron filtration rate (SNGFR) via interaction with angiotensin II (AII) was tested by renal micropuncture. The physical determinants of SNGFR were assessed in adult male Munich Wistar rats 5-7 d after ipsilateral surgical renal denervation (DNX). DNX was performed to isolate inhibitory central and presynaptic alpha 2 adrenoceptors from end-organ receptors within the kidney. Two experimental protocols were employed: one to test whether prior AII receptor blockade with saralasin would alter the glomerular hemodynamic response to alpha 2 adrenoceptor stimulation with the selective agonist B-HT 933 under euvolemic conditions, and the other to test whether B-HT 933 would alter the response to exogenous AII under conditions of plasma volume expansion. In euvolemic rats, B-HT 933 caused SNGFR to decline as the result of a decrease in glomerular ultrafiltration coefficient (LpA), an effect that was blocked by saralasin. After plasma volume expansion, B-HT 933 showed no primary effect on LpA but heightened the response of arterial blood pressure, glomerular transcapillary pressure gradient, and LpA to AII. The parallel results of these converse experiments suggest a complementary interaction between renal alpha 2-adrenergic and AII systems in the control of LpA.

NASA Discipline Cardiopulmonary↗
DOE OSTI2018

Collisionless coupling of a high- β expansion to an ambient, magnetized plasma. II. Experimental fields and measured momentum coupling

The momentum coupled to a magnetized, ambient argon plasma from a high-β, laser-produced carbon plasma is researched in a collisionless, weakly coupled limit. The total electric field was measured by separately examining the induced component associated with the rapidly changing magnetic field of the high-β (kinetic β~10 6 ), expanding plasma and the electrostatic component due to polarization of the expansion. Their temporal and spatial structures are discussed and their effect on the ambient argon plasma (thermal β~10 –2 ) is confirmed with a laser-induced fluorescence diagnostic, which directly probed the argon ion velocity distribution function. For the given experimental conditions, the electrostatic field is shown to dominate the interaction between the high-β expansion and the ambient plasma. Particularly, the expanding plasma couples energy and momentum into the ambient plasma by pulling ions inward against the flow direction.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1986

A plasma generator utilizing the high intensity ASTROMAG magnets

The magnet configuration for the proposed particle astrophysics magnet facility (ASTROMAG) on the space station includes a cusp magnetic field with an intensity of a few tesla. With these large magnets (or others) located in the outer ionosphere, many quite interesting and unique plasma physics experiments become possible. First there are studies utilizing the magnet alone to examine the supersonic, sub-Alfvenic interaction with the ambient medium; the scale length for the magnet perturbation is approx. 20 m. The magnetic field geometry when combined with the Earth's and their relative motion will give rise to a host of plasma phenomena: ring nulls, x-points, ion-acoustic and lower-hybrid shocks, electron heating (possible shuttle glow without a surface) launching of Alfvenwaves, etc. Second, active experiments are possible for a controlled study of fundamental plasma phenomena. A controlled variable species plasma can be made by using an RF ion source; use of two soft iron rings placed about the line cusp would give an adequate resonance zone (ECH or ICH) and a confining volume suitable for gas efficiency. The emanating plasma can be used to study free expansion of plasma along and across field lines (polar wind), plasma flows around the space platform, turbulent mixing in the wake region, long wavelength spectrum of convecting modes, plasma-dust interactions, etc.

Sullivan, James D.↗
DOE OSTI2013

The high-energy-density counterpropagating shear experiment and turbulent self-heating

The counterpropagating shear experiment has previously demonstrated the ability to create regions of shock-driven shear, balanced symmetrically in pressure, and experiencing minimal net drift. This allows for the creation of a high-Mach-number high-energy-density shear environment. New data from the counterpropagating shear campaign is presented, and both hydrocode modeling and theoretical analysis in the context of a Reynolds-averaged-Navier-Stokes model suggest turbulent dissipation of energy from the supersonic flow bounding the layer is a significant driver in its expansion. A theoretical minimum shear flow Mach number threshold is suggested for substantial thermal-turbulence coupling.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗