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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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Ballooning mode instability at the plasmapause

The ballooning mode instability, which can excite hydromagnetic waves at the plasmapause, is studied in the presence of azimuthal plasma flows induced during geomagnetically disturbed periods. A general sufficient criterion for the ballooning mode stability is derived, for a change in the potential energy greater than or equal to 0, which involves the integration over an entire field line. A local stability analysis at the equatorial plasmapause region shows that the ballooning modes could be spontaneously generated via instability under at least two conditions: one is similar to the usual interchange condition, and the second to the quasi-interchange modes. Both of these local instability conditions can be derived from the general stability criterion. Finally an exact solution for the equilibrium state with flow is derived analytically, and the change in the potential energy is computed numerically. It is found that, in the cases studied, the flow does not spontaneously excite the ballooning modes; it only further stabilizes (or destabilizes) the ballooning spectrum if originally the system is stable (or unstable). The analysis would be useful for the interpretation of some of the low-frequency modes observed at the ground and near the equatorial plasmapause.

Lakhina, G. S.↗
NASA NTRS1994

Anisotropic Alfven-ballooning modes in Earth's magnetosphere

We have carried out a theoretical analysis of the stability and parallel structure of coupled shear Alfven and slow magnetosonic waves in Earth's inner magnetopause (i.e., at equatorial distances between about five and ten Earth radii) including effects of finite anisotropic Grad-Shafranov equation yields an approximate self-consistent magnetohydrodynamic (MHD) equilibrium. This MHD equilibrium is used in the numerical solution of a set of eigenmode equations which describe the field line eigenfrequency, linear stability, and parallel eigenmode structure. We call these modes anisotropic Alfven-ballooning modes. The main results are: (1) The field line eigenfrequency can be significantly lowered by finite pressure effects. (2) The parallel mode structure of the transverse wave components is fairly insensitive to changes in the plasma pressure, but the compressional magnetic component can become highly peaked near the magnetic equator as a result of increased pressure, especially when P(sub perpendicular to) is greater than P(sub parallel) (here P(sub perpendicular to) and P(sub parallel) are the perpendicular and parallel plasma pressure). (3) For the isotropic (P(sub parallel) = P(sub perpendicular to) = P) case ballooning instability can occur when the ratio of the plasma presure to the magnetic pressure, beta = P/(B squared/8 pi), exceeds a critical value beta(sup B)(sub 0) is approximately equal to 3.5 at the equator. (4) Compared to the isotropic case the critical beta value is lowered by anisotropy, either due to decreased field line bending stabilization when P(sub parallel) is greater than P(sub perpendicular to) or due to increased ballooning-mirror destabilization when P(sub perpendicular to) is greater than P(sub parallel). (5) We use a beta-delta stability diagram to display the regions of instability with respect to the equatorial values of the parameters bar beta and delta, where bar beta = (1/3)(beta(sub parallel) + 2 beta(sub perpendicular to)) is an average beta value and delta = 1 - P(sub parallel)/P(sub perpendicular to) is a measure of the plasma anisotropy. The diagram is divided into regions corresponding to the firehose, mirror and ballooning instabilities. It appears that observed values of the plasma pressure are below the critical value for the isotropic ballooning instability but it may be possible to approach a ballooning-mirror instability when P(sub perpendicular to)/P(sub parallel) is greater than or approximately 2.

Chan, Anthony A.↗
NASA NTRS1986

Resistive ballooning modes in line-tied coronal arcades

The equations describing the linear evolution of resistive ballooning modes are obtained by using a modified WKB expansion in the short perpendicular wavelength, while variations of the perturbations along the field are described by a slowly varying amplitude, on which the tying boundary conditions are imposed. In general, given an equilibrium, there are certain ranges of magnetic surfaces for which the system predicts instability even without dissipation. The main conclusion is that within the resistive MHD approximation cylindrically symmetric arcades with pressure falling with radius are unstable to resistive localized modes; the growth rates, close to ideal marginal stability, are large, so that it would appear that energy could be released during 10 to 100 Alfven times. The wavelength of the modes is expected to be limited by the ion gyroradius, when stabilizing drift effects must be taken into account. The nonlinear evolution of resistive ballooning modes should be studied to assess their overall relevance to the violent and rapidly evolving phenomena observed on the sun.

Velli, Marco↗
NASA NTRS1988

Current-driven resistive ballooning modes in axially bounded solar flare plasmas

The most unstable current-driven resistive modes of an axially bounded coronal loop are found in computer simulations to exhibit the spatial structure of ballooning modes. The observed modes are not confined to mode rational surfaces, but instead have broad radial extent. A theory assuming ballooning mode spatial structure predicts that a minimum current should be required for linear instability, and that, when the mode is unstable, the linear growth rate scales linearly with the resistivity eta below a critical resistivity, and scales as cu root of eta for larger resistivities. Both predictions are borne out by simulation results. Both theory and simulation analyses of the mode suggest that the strong radial structure of the mode near the ends of the system is the primary contributing factor to the instability of the mode. A helical current sheet is formed in the nonlinear evolution of the mode near the edge of the current channel and is accompanied by a strong radial gradient in the current and partial current reversal.

Otani, Niels F.↗
NASA NTRS1989

The effect of ballooning modes on thermal transport and magnetic field diffusion in the solar corona

Presently favored mechanisms of coronal heating (current sheet dissipation and Alfven wave resonant heating) deposit heat in thin layers. Classical thermal conduction cannot explain how heat is transported across the magnetic field. If heating occurs in thin layers, large pressure gradients can be created which can give rise to ballooning modes. These instabilities are caused by the pressure gradient and the curvature of the magnetic field, and are stabilized by magnetic tension. The modes are broad band in wavelength and should produce turbulence. A mixing length expression for the turbulent heat transport shows that it is more than adequate to rapidly convect heat into much broader layers. Furthermore, the turbulent resistivity implies that heating occurs over most of the width of these broadened layers. The broadening also implies that much shorter time scales are required for heating. The beta values in the corona suggest that 1-10 turbulent layers are formed in typical loop or arch structures.

Strauss, H. R.↗
NASA NTRS1990

Ballooning instability of the earth's plasma sheet region in the presence of parallel flow

Stability of the plasma sheet and plasma sheet boundary layer against the ballooning mode instability is investigated. The equilibrium state of a two-dimensional plasma sheet configuration with parallel sheared flow is modeled. This equilibrium is shown to be ballooning unstable when delta-W is not positive definite, where delta-W is the potential energy. The eigenmode structure of the ballooning mode is found by imposing the boundary conditions that the waves are totally reflected from the ionosphere, and that no waves are coming in from infinity. The eigenmode structure of the unstable balloning modes is highly oscillatory, extending beyond about 100 R(E). The ballooning modes are thus a possible candidate for explaining the MHD waves and other dynamical events observed in the magnetotail by ISEE 3 and other spacecraft.

Lakhina, G. S.↗
NASA NTRS1989

Ballooning stability of axisymmetric plasmas with sheared equilibrium flows

A WKB theory is formulated for large-n ballooning modes in axisymmetric, toroidal plasmas with sheared equilibrium flows. The validity of the standard ballooning respresentation is severely restricted in the presence of sheared toroidal flow, despite the fact that to leading order in (1/n), where n is the azimuthal number, the eigenmode equation contains only derivatives along a field line. Necessary and sufficient conditions for stability are obtained in a high-beta ordering for rigid toroidal rotation as well as field-aligned flows.

Bhattacharjee, A.↗
NASA NTRS1981

Nonlinear magnetohydrodynamic stability

The computer code developed by Bauer et al. (1978) for the study of the magnetohydrodynamic equilibrium and stability of a plasma in toroidal geometry is extended so that the growth rates of instabilities may be estimated more accurately. The original code, which is based on the variational principle of ideal magnetohydrodynamics, is upgraded by the introduction of a nonlinear formula for the growth rate of an unstable mode which acts as a quantitative measure of instability that is important in estimating numerical errors. The revised code has been applied to the determination of the nonlinear saturation, ballooning modes and beta limits for tokamaks, stellarators and torsatrons.

Bauer, F.↗
NASA NTRS1972

Stably trapped proton limits for Jupiter

A general introduction to pitch-angle diffusion for Earth and Jupiter magnetospheres is given. The instabilities which might limit the trapped fluxes in the earth magnetosphere are identified as the interchange or ballooning mode, electrostatic loss cone modes, and electromagnetic ion cyclotron wave. The instability theory of the ion cyclotron wave is discussed. This wave can be unstable only if protons can be in cyclotron resonance with the wave. The instability growth rate is proportional to the cyclotron frequency, the fractional number density of fast particles, and the anisotropy of the fast particle distribution. The critical proton energy is the lowest energy for which the stably trapped limit applies, and is calculated to be 150 MeV at L = 2 and for 10 ion pairs/cu cm. Particles above the critical threshold energy are considered and their stability limit is approximately 3 x 10 to the 10th power/sq cm/sec divided by L to the 4th power.

Kennel, C.↗
NASA NTRS1982

An assessment of the FGGE satellite observing system during SOP-1

The sensitivity of a Goddard Laboratory for Atmospheric Sciences global objective analysis cycle to the addition of FGGE level II-b data is assessed. The GOAS system comprises a predictive continuity provided by a model first-guess forecast integrated from a previous forecast and updated by data gathered in the interim. FGGE data originated in the Jan.-Mar. 1979 period and were acquired by rawinsondes, pilot balloons, surface stations, satellites, ships, and drifting buoys deployed during SOP-1. Focussing on 2-5 and 8-day forecasts, comparisons were made of the 6 hr forecast error at the 300 mb height in three experiments using all, no-satellite (NOSAT), and without rawinsondes or pilot balloons modes. Larger errors occurred in the case of NOSAT, while significant corrections to the GOAS predictions were noted using all the FGGE data. It was concluded that all forecasts were improved by inclusion of full FGGE data sets, including forecasting beyond one week.

Halem, M.↗
NASA NTRS1989

Nonlinear twist-kink instability of a coronal loop

Three-dimensional magnetoinductive particle simulations are used to demonstrate that the mechanical twisting motion applied to a magnetized plasma column induces a current aligned to the external magnetic field direction, pinches the plasma and magnetic fields, and stores the energy in poloidal magnetic fields. As the twist motion continues, the field lines locally begin to wrap around the plasma more than one revolution. A strong MHD instability sets in that is a mixture of kink and ballooning modes, releasing the magnetic energy and causing destruction of coherent column structure and flows of turbulent plasma. A similar episode ensues, exhibiting relaxation oscillations. The buildup of poloidal fields and structure and its sudden release driven by the twist motion may be a model for the solar coronal loop dynamics which exhibits a slow energy buildup with some photospheric motion and a sudden energy release by flares.

Zaidman, E. G.↗
NASA NTRS1990

Ballooning stability of anisotropic, rotating plasmas

The linearized equation of motion is given in a Lagrangian representation for a rotating plasma with anisotropic pressure. A WKB theory is developed for large-n ballooning modes in an axisymmetric configuration with field-aligned and rigid toroidal flows. In the presence of field-aligned flows, it is shown that a resonance occurs which is strongly suggestive of a generalized mirror instability. In the presence of toroidal rotation, a possible stabilizing effect is identified for P(normal) greater than P(parallel). Finally, as a special case of the theory, the necessary and sufficient conditions for stability in a static, anisotropic plasma are obtained.

Wang, X.-H.↗
NASA NTRS1990

Thermal emission spectroscopy of the middle atmosphere

The general objective of this research is to obtain, via remote sensing, simultaneous measurements of the vertical distributions of stratospheric temperature, ozone, and trace constituents that participate in the catalytic destruction of ozone (NO(sub y): NO, NO2, NO3, HNO3, ClONO2, N2O5, HNO4; Cl(sub x): HOCl), and the source gases for the catalytic cycles (H2O, CH4, N2O, CF2Cl2, CFCl3, CCl4, CH3Cl, CHF2Cl, etc.). Data are collected during a complete diurnal cycle in order to test our present understanding of ozone chemistry and its associate catalytic cycles. The instrumentation employed is an emission-mode, balloon-borne, liquid-nitrogen-cooled Michelson interferometer-spectrometer (SIRIS), covering the mid-infrared range with a spectral resolution of 0.020 cm(exp -1). Cryogenic cooling combined with the use of extrinsic silicon photoconductor detectors allows the detection of weak emission features of stratospheric gaseous species. Vertical distributions of these species are inferred from scans of the thermal emission of the limb in a sequence of elevation angles. The fourth SIRIS balloon flight was carried out from Palestine, Texas on September 15-16, 1986 with 9 hours of nighttime data (40 km). High quality data with spectral resolution 0.022 cm(exp -1), were obtained for numerous limb sequences. Fifteen stratospheric species have been identified to date from this flight: five species from the NO(sub y) family (HNO3, NO2, NO, ClONO2, N2O5), plus CO2, O3, H2O, N2O, CH4, CCl3F, CCl2F2, CHF2Cl, CF4, and CCl4. The nighttime values of N2O5, ClONO2, and total odd nitrogen have been measured for the first time, and compared to model results. Analysis of the diurnal variation of N2O5 within the 1984 and 1986 data sets, and of the 1984 ClONO2 measurements, were presented in the literature. The demonstrated ability of SIRIS to measure all the major NO(sub y) species, and therefore to determine the partitioning of the nitrogen family over a continuous diurnal cycle, is a powerful tool in the verification and improvement of photochemical modeling.

Kunde, V. G.↗
NASA NTRS1992

Is the earth's magnetotail balloon unstable?

In the past, the onset of magnetospheric substorms has been attributed to the plasma tearing mode instabilities. This paper investigates the ideal MHD ballooning instability of the near-and middle-tail magnetosphere region, as a first step toward determining whether it could trigger the tearing mode, by using the energy principle to investigate whether standard 2D tail models with the 'hard' ionospheric boundary condition are unstable to ballooning instability. Numerical results are presented for compressible ballooning modes that are symmetric about the center of the current sheet. It is shown that, for such a hard boundary condition, no reasonable magnetotail configuration exists that would be unstable to compressible symmetric ballooning but stable against interchange.

Lee, D.-Y.↗
NASA NTRS1989

Fracture characteristics of balloon films

An attempt was made to determine the failure modes of high altitude scientific balloons through an investigation of the fracture characteristics of the thin polyethylene films. Two films were the subject of the evaluation, Winzen Int.'s Stratafilm SF-85 and Raven Industries' Astro-E. Research began with an investigation of the film's cold brittleness point and it's effect on the ultimate strength and elasticity of the polyethylene film. A series of preliminary investigations were conducted to develop an understanding of the material characteristics. The primary focus of this investigation was on the notch sensitivity of the films. Simple stress strain tests were also conducted to enable analysis employing fracture toughness parameters. Studies were conducted on both film types at 23 C (room temperature), -60 C, -90 C, and -120 C.

Portanova, Marc A.↗
NASA NTRS2008

Study of Molecular Line Parameters down to Very Low Temperature

The impact of precise spectroscopic measurements on the P(9) multiplet in the v3 band of 12CH4, obtained using a newly developed cold Herriott cell coupled with a tunable diode laser spectrometer, is examined in the context of remote sensing of methane in the atmosphere. More specifically, the influence of the air-broadening temperature dependence, of line narrowing and of line-mixing effects is assessed when fitting high resolution atmospheric spectra recorded from a balloon in the solar occultation mode. This is achieved by considering residuals and retrieved methane volume mixing ratio profiles. By combining data from previous studies together with new measurements, the expression for the temperature dependence of the broadening coefficient has been revisited. It is shown that a correcting factor applied to the usual law gives better results, when considering all the available measurements from room temperature down to about 10-20 K, as compared to the usual expression of the width versus temperature. These results clearly demonstrate that collision broadening is more sensitive to long-range attractive forces when the temperature is decreased.

Mondelain, D.↗
NASA NTRS1973

Stability analysis and trend study of a balloon tethered in a wind, with experimental comparisons

A stability analysis and trend study for a balloon tethered in a steady wind are presented. The linearized, stability-derivative type analysis includes balloon aerodynamics, buoyancy, mass (including apparent mass), and static forces resulting from the tether cable. The analysis has been applied to a balloon 7.64 m in length, and the results are compared with those from tow tests of this balloon. This comparison shows that the analysis gives reasonable predictions for the damping, frequencies, modes of motion, and stability boundaries exhibited by the balloon. A trend study for the 7.64-m balloon was made to illustrate how the stability boundaries are affected by changes in individual stability parameters. The trends indicated in this study may also be applicable to many other tethered-balloon systems.

Redd, L. T.↗