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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Dependence of ion-cyclotron range of frequencies instabilities on species mix and fast-ion distribution: III. Novel sub-cyclotron modes

Dedicated DIII-D experiments studied instabilities above and below the ion cyclotron frequency by injecting thirteen different neutral beam populations into L-mode plasmas with different thermal compositions of H, D, and 3 He at five different values of toroidal field. Two companion papers describe the results of these experiments in detail. This paper focuses on data and analysis of two instabilities that occur at ${\sim}0.6$ of the deuterium and hydrogen cyclotron frequencies $f_\mathrm {cD}$ and $f_\mathrm {cH}$ in mixed hydrogen and deuterium plasmas. The modes below $f_\mathrm {cD}$ are often driven unstable by deuterium beams but are rarely destabilized by hydrogen beams. The modes below $f_\mathrm {CD}$ are reported here for the first time in a fusion plasma. These $\mathrm{sub-}f_\mathrm {cH}$ modes are only driven by deuterium beams but, unlike the $\mathrm{sub-}f_\mathrm {cD}$ modes, they are only unstable in plasmas with deuterium concentrations that are ${\lesssim}20\%$; they also have a smaller amplitude than the sub-deuterium modes. Addition of fully-ionized 3 He to the plasma has little effect on the sub-cyclotron deuterium modes but is stabilizing for the sub-cyclotron hydrogen modes. The modes are excited in the core and have toroidal mode numbers around 20. These trends are compared with calculations of the growth rate in a simplified model. The theory successfully predicts global Alfvén eigenmode instability with frequencies and mode numbers close to experimental values, the stronger amplitude of the sub-deuterium modes, and the species-mix dependence of the sub-hydrogen modes. Increased damping associated with the ion-ion hybrid, cutoff, and crossover frequencies plausibly accounts for the stabilization of the $\mathrm{sub-}f_\mathrm {cH}$ modes when 3 He is puffed. However, the relative stability of $\mathrm{sub-}f_\mathrm {cH}$ modes during hydrogen injection remains unexplained.

electromagnetic ion cyclotron instability↗
NASA NTRSDate not supplied

Observations of Ion-Scale Cyclotron Waves and Their Relationship with Non-thermal Ion Distributions in the Solar Wind

Introduction - Electromagnetic cyclotron waves (ECWs) near the proton cyclotron frequency (f_pc) and higher than Alfvén wave frequency - Ion cyclotron waves (ICWs): left-hand (LH) polarized in plasma frame - Magnetosonicwaves: right-hand (RH) polarized in plasma frame - They are important because the absorption of fluctuating magnetic field energy starting at f_pc has been demonstrated extensively - Before PSP era, intermittent observations of such ECWs in quiet solar wind have been reported in Behannon (1976), Tsurutani et al. (1994), Jian et al. (2009, 2010, 2014), Boardsen et al. (2015), Wicks et al. (2016), etc

L K Jian↗
NASA NTRS1989

Anisotropy of shock-accelerated ion distributions in interplanetary space

The discrepancy between theory and observation is discussed with regard to the ability of interplanetary shock waves to accelerate a small percentage of the thermal ion population. The major point of departure rests with the spatial dependence of the energetic particle intensity and anisotropy in the region upstream of interplanetary shocks. It is argued that the discrepancy is due to the presence of solar flare particles forming an additional seed population which alters the upstream boundary condition of the energetic population. The resulting anisotropy of the energetic particle distribution several scale lengths upstream of the shock is proportional to the ratio of the streaming of the shock-accelerated population to the density of the solar flare population. This theory is then compared with the results of observed upstream anisotropy and measured particle intensities and anisotropies.

Smith, Charles W.↗
NASA NTRS1988

Three-dimensional magnetosheath plasma ion distributions from 200 eV to 2 MeV

This paper presents initial measurements, made with ISEE 1 plasma and energetic-particle instruments, of the three-dimensional magnetosheath plasma ion flow and the spectrum over the energy range of 200 eV to 2 MeV, obtained on two magnetosheath traversals, one on the dawn (December 19, 1977) and the other on the dusk (July 7, 1978) flanks of the magnetosphere. The data suggest that the magnetosheath plasma ion population often consisted of a shocked solar wind component, of energy not greater than 5 keV, and a magnetospheric high-energy (not below 5 keV) component. The shocked solar wind component generally behaved independently of the magnetic field direction, indicating that the magnetic field was carried along in the bulk plasma flow. The high-energy tail was highly modulated by the magnetic field.

Williams, D. J.↗
NASA NTRS1997

Change in Ion Distribution Function While Crossing the Space Shuttle Wake

During the space shuttle/Spacelab 2 mission (STS-5]F) the Plasma Diagnostic Package (PDP) was placed in free flight in the vicinity of the Orbiter and provided the first opportunity to measure the midwake and far-wake regions of an orbiting spacecraft. During this period the PDP crossed the wake 4 times at downstream distances ranging from 40 m to 240 m. During each crossing a definite change in the ion-retarding potential curves was measured when the PDP was in the shuttle wake compared to the ambient ionosphere. These measurements were obtained by both the differential ion flux probe and the retarding potential analyzer instruments on the PDP. The temperature of the ions, derived from fitting the data to a Maxwellian distribution, are consistent with an enhancement during each wake crossing of as much as a factor of 2.5 (from about 0.08 eV to 0.2 eV). Such studies of plasma wakes were never before performed.

Sorensen, J. E.↗
NASA NTRS1993

Comment on 'Comparison of observed and calculated implanted ion distributions outside Comet Halley's bow shock' by T. I. Gombosi, M. Neugebauer, A. D. Johnstone, A. J. Coates, and D. E. Huddleston

It is argued that the formulation used by Gombosi (1991) does not distinguish between two fundamental types of resonant interactions (those between cometary pickup ions and LF electromagnetic waves). Two problems arise from using their overly simplified expressions. The wave polarization of the solar wind Alfven wave is not purely right-handed, and values from alpha sub com and alpha sub sw are not well known, nor are the 'polarizations' of the 'backward'-going waves in either case. Gombosi et al. discuss the antisunward vs the sunward propagating solar wind Alfven wave, and assume a reasonable value of 0.2 for alpha sub sw. However, alpha sub com is totally unknown. It is concluded that a more correct analysis of wave polarization can lead to significant changes in the formulation and results from Gombosi et al. In his reply Gombosi argues that his simplified wave-particle interaction model is consistent with Giotto observations and plasma kinetic simulations and it leads to a reasonable approximation of the implanted ion transport coefficients. The more complicated approach suggested by Tsurutani & Thorne (1993) requires the introduction of several ad hoc parameters and it does not lead to any change of the energy diffusion coefficient.

Tsurutani, Bruce T.↗
NASA NTRS1982

Ion distribution effects of turbulence on a kinetic auroral arc model

An inverted-V auroral arc structure plasma-kinetic model is extended to phenomenologically include the effects of electrostatic turbulence, with k-parallel/k-perpendicular being much less than unity. It is shown that, unless plasma sheet ions are very much more energetic than the electrons, anomalous resistivity is not a large contributor to parallel electrostatic potential drops, since the support of the observed potential drop requires a greater dissipation of energy than can be provided by the plasma sheet. Wave turbulence can, however, be present, with the ion cyclotron turbulence levels suggested by the ion resonance broadening saturation mechanism of Dum and Dupree (1970) being comparable to those observed on auroral field lines. The diffusion coefficient and net growth rate are much smaller than estimates based solely on local plasma properties.

Cornwall, J. M.↗
NASA NTRS1982

Plasmaspheric helium ion distribution from satellite observations of He II 304-A

High sensitivity and spatial resolution observations of the He II 304-A emission line intensity in the earth's nightglow have been carried out by the extreme ultraviolet telescope on the Apollo-Soyuz mission in July, 1975. The data, obtained over a wide range of plasmasphere parameters, are compared to the predictions of a kinetic equilibrium model of plasmaspheric ion density. Excellent agreement between observation and theory is found using as inputs a temperature model, solar flux and H(+) and O(+) number densities determined by extrapolating nearly simultaneous Atmospheric Explorer C measurements at 300 km. The observations in the Northern Hemisphere are well fit by a model having 285 He(+) ions/cu cm at 500 km independent of latitude or longitude, while those in the south require 430 He(+) ions/cu cm at the same altitude. This result is consistent with available information on the interhemispheric asymmetry of He(+) observed by a mass spectrometer on Explorer 32 and on the winter neutral helium bulge.

Chakrabarti, S.↗
NASA NTRS1973

Yield and ion distribution for the barium cloud at 31,000 kilometers, September 21, 1971.

The photon flux density associated with the 4554-A resonance radiation for Ba II was measured at Mount Hopkins, Arizona, and Cerro Morado, Chile, and was determined to be 36,000 photon/sq cm sec outside the atmosphere; this measurement was made when the cloud was optically thin at 120 sec after release. Using this and a photon scattering efficiency of 0.66 photon/ion sec we estimate a 1.7-kg yield of barium ions that are formed from the initially released atomic barium and are thus associated with the main core of the cloud. Photographic and photometric data are combined to obtain preliminary values for the brightness throughout the cloud for two photographs, and isobrightness plots are presented. These plots indicate that the cloud is quite narrow, that a considerable portion of the ionized barium is outside the main core after a few minutes, and that the striations contain only a small fraction of the total material.

Manring, E. R.↗
DOE OSTI2026

Ion Distribution and Cation Exchange at Mica–Electrolyte Interfaces Probed with Deep Potential Molecular Dynamics

Here, we investigate the Stern layer structure and cation exchange mechanism at muscovite mica-electrolyte interfaces using nanosecond timescale molecular dynamics simulations based on deep neural network interatomic potentials trained on Density Functional Theory (DFT) data. Focusing on mica with exposed surface K + interfaced with aqueous NaCl and mica with surface Na + interfaced with KCl solution, we find that K + remains predominantly in inner-sphere configurations, while Na + exhibits notable populations in outer-sphere states. Most importantly, our simulations show that contact with an electrolyte solution results in the co-adsorption of multiple cation species, making the mica surface locally overcharged and thus reshaping the cation speciation in a manner that enhances the tendency of neighboring surface cations to desorb. These findings are consistent with recent experimental observations that co-adsorption of different cation species induces changes in cation speciation and slow kinetics of cation exchange at the muscovite-water interface, providing a basis for their detailed understanding.

36 MATERIALS SCIENCE↗