Energetic Ion Fluxes Research Articles

Modulation of auroras by Pc5 pulsations in the dawn sector in association with reappearance of energetic particles at geosynchronous orbit

Geomagnetic Pc5 pulsations were observed in the dawn sector of the auroral zone on 17 January 1994 in association with increased energetic ion fluxes at geosynchronous orbit 10min after the Pi2 onset. The characteristic properties of auroras associated with these pulsations were studied using movies taken by an all-sky imager. It was found that a pulsating aurora (PA) can be an optical manifestation of the Pc5 waves by a strong poloidal component observed with ground-based magnetometers. Goes7 observations showed compressional pulsations with the same period which can be attributed to the influence of the finite pressure of plasma and field line curvature on the poloidally polarized Alfvén waves. These poloidal pulsations may be generated by the ion injection observed with the LANL 1989-046 satellite. Two auroral arcs were observed north of the PA with optical features characteristic for the toroidal field line resonances: strong localization across L-shells, 180° phase change across the resonance, poleward phase propagation. Thus the Pc5 oscillations split into the toroidal and poloidal mode and oscillated coherently at latitudes from 62°N to 70°N. This study provides observational evidence of polarization splitting of the Alfven oscillation spectrum. Such a polarization splitting would occur in association with the reappearance of the energetic particles at geosynchronous orbit.

Observations of energetic particles in the upstream of a quasi-parallel collisionless shock

通过Cluster卫星在2005年3月16日观测到的一个准平行激波观测事例，研究了准平行激波上游低频等离子体波动与能量离子之间的关系.卫星观测结果表明，在准平行激波上游，离子微分能通量受到了非线性波动的调制.在磁场强度较小区域，离子微分能通量较高.产生这种现象的可能原因是准平行激波上游的非线性波动可以捕获离子，被捕获的离子在波动中来回弹跳并被电场加速，从而导致磁场强度较小区域离子微分能通量较高.这一观测结果与已有的混合模拟结果相吻合.

OBSERVATIONS OF ENERGETIC PARTICLES BETWEEN A PAIR OF COROTATING INTERACTION REGIONS

We report observations of the acceleration and trapping of energetic ions and electrons between a pair of corotating interaction regions (CIRs). The event occurred in Carrington Rotation 2060. Observed at spacecraft STEREO-B, the two CIRs were separated by less than 5 days. In contrast to other CIR events, the fluxes of energetic ions and electrons in this event reached their maxima between the trailing-edge of the first CIR and the leading edge of the second CIR. The radial magnetic field (Br) reversed its sense and the anisotropy of the flux also changed from sunward to anti-sunward between the two CIRs. Furthermore, there was an extended period of counter-streaming suprathermal electrons between the two CIRs. Similar observations for this event were also obtained for ACE and STEREO-A. We conjecture that these observations were due to a "U-shape" large scale magnetic field topology connecting the reverse shock of the first CIR and the forward shock of the second CIR. Such a disconnected U-shaped magnetic field topology may have formed due to magnetic reconnection in the upper corona.

MHD and kinetic analysis of flow bursts in the Earth’s plasma sheet

In an attempt to study the flow bursts in the Earth’s plasma sheet we select an event that took place on August 7, 2004 in the expansion phase of a substorm, using data from the geomagnetic index, solar wind data, plasma and magnetic field observations from C1 Cluster satellite (the Cluster mission has 4 satellites) and from Double Star TC-1 satellite. In MHD approach, TC-1 firstly observed the tailward flow, then the earthward, and finally the flow alternated in two directions. C1 firstly observed the earthward plasma flow, and then the tailward plasma flow. Before flow bursts are observed by TC-1 and C1, there are disturbances in local entropy with their tailward local entropy larger than those of the earthward. The kinetic features of the plasma flow observed by C1 are similar to those in MHD. However, kinetic characteristics of the plasma flow observed by TC-1 are far more than the description in MHD. The inadequacy mainly exists in two cases: (i) the firstly enhanced tailward flows given in MHD are found without significant increase of the energetic tailward flux; (ii) the almost stagnant flow in MHD is composed of the enhanced energetic ion flux in both earthward and tailward directions. The earthward flow burst observed by TC-1 might be multiple overshoots and rebounds. The earthward flow burst observed by C1 might be simply rebounded in the near-Earth. The pulsation observed by C1 is earlier than that observed by TC-1 with the former intensity less than that of the latter. After the energetic ion flux in the tailward direction is significantly enhanced, the power spectrum intensity of the ULF wave commences to increase obviously, which may suggest that the stream instability is closely correlated with ULF pulsations.

THE SOLAR WIND AS A POSSIBLE SOURCE OF FAST TEMPORAL VARIATIONS OF THE HELIOSPHERIC RIBBON

We present a possible source of pickup ions (PUIs) the ribbon observed by the Interstellar Boundary EXplorer (IBEX). We suggest that a gyrating solar wind and PUIs in the ramp and in the near downstream region of the termination shock (TS) could provide a significant source of energetic neutral atoms (ENAs) in the ribbon. A fraction of the solar wind and PUIs are reflected and energized during the first contact with the TS. Some of the solar wind may be reflected propagating toward the Sun but most of the solar wind ions form a gyrating beam-like distribution that persists until it is fully thermalized further downstream. Depending on the strength of the shock, these gyrating distributions can exist for many gyration periods until they are scattered/thermalized due to wave-particle interactions at the TS and downstream in the heliosheath. During this time, ENAs can be produced by charge exchange of interstellar neutral atoms with the gyrating ions. In order to determine the flux of energetic ions, we estimate the solar wind flux at the TS using pressure estimates inferred from in situ measurements. Assuming an average path length in the radial direction of the order of a few AU before the distribution of gyrating ions is thermalized, one can explain a significant fraction of the intensity of ENAs in the ribbon observed by IBEX. With a localized source and such a short integration path, this model would also allow fast time variations of the ENA flux.

The free escape continuum of diffuse ions upstream of the Earth's quasi‐parallel bow shock

The Earth's bow shock is very efficient in accelerating ions out of the incident solar wind distribution to high energies (≈ 200 keV/e). Fluxes of energetic ions accelerated at the quasi‐parallel bow shock, also known as diffuse ions, are best represented by exponential spectra in energy/charge, which require additional assumptions to be incorporated into these model spectra. One of these assumptions is a so‐called “free escape boundary” along the interplanetary magnetic field into the upstream direction. Locations along the IBEX orbit are ideally suited for in situ measurements to investigate the existence of an upstream free escape boundary for bow shock accelerated ions. In this study we use 2 years of ion measurements from the background monitor on the IBEX spacecraft, supported by ACE solar wind observations. The IBEX Background Monitor is sensitive to protons > 14 keV, which includes the energy of the maximum flux for diffuse ions. With increasing distance from the bow shock along the interplanetary magnetic field, the count rates for diffuse ions stay constant for ions streaming away from the bow shock, while count rates for diffuse ions streaming toward the shock gradually decrease from a maximum value to ~1/e at distances of about 10 RE to 14 RE. These observations of a gradual decrease support the transition to a free escape continuum for ions of energy >14 keV at distances from 10 RE to 14 RE from the bow shock.

High-Energy-Density Pinch Plasma: A Unique Nonconventional Tool for Plasma Nanotechnology

Low-temperature (<; 10 eV) plasmas with densities varying over a very wide range from 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sup> m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> at the lower end to as high as 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">23</sup> m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> have firmly established themselves as one of the most efficient and versatile tools to create and process materials at nanoscale. The dense plasma focus (DPF) device, which is a noncylindrical <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Z</i> -pinch facility that compresses the plasma to very high energy densities, offers a complex mix of high energy ions of the filling gas species, immensely hot and dense decaying plasma, fast-moving ionization wave front, and a strong shockwave that provides a unique plasma and a physical/chemical environment that is completely unheard of in any other conventional plasma-based deposition or processing facility. This review aims to highlight the novel features offered by pulsed high-energy-density pinch plasmas from a DPF, having temperatures and densities a few orders of magnitudes higher than conventional low-temperature plasmas, in the processing and the synthesis of materials at nanoscale. The nanoscale fabrication using the DPF device is elaborated and discussed in two broad categories: 1) top-down nanoscale fabrication by processing of bulk or thin-film target materials that are placed downstream the anode axis by the energetic transient flux of energetic ions, the hot decaying plasma, the fast ionization wave front, and the shock front; and 2) bottom-up nanoscale fabrication by deposition of nanostructured thin films of metals and/or their nitrides, carbides, and oxides by ablating the metal fitted on to the anode top under suitable reactive or inert background plasma.

Nonturbulent stabilization of ion fluxes by the fan instability

Abstract Resonant interactions between energetic ion fluxes and wave packets they excite through fan instability are studied using self-consistent 3D simulations to explain the nonlinear wave–particle mechanisms at work and to estimate the energy lost by the flux and its sharing between wave emission and particle heating. The saturation of waves and the relaxation of particles are studied over long time periods. The ions are not only diffusing in the waves but are also trapped simultaneously by several potential wells of large amplitude overlapping waves. Estimates of the ion heating energy and rate are given and compared with space observations.

Ionospheric characteristics associated with wave–particle interactions in a SED plume during a super geomagnetic storm

We report some interesting ionospheric characteristics associated with wave–particle interactions with observations of the ionosonde and co-located incoherent scatter radar (ISR) at Millstone Hill in a storm-enhanced density (SED) plume identified from two-dimensional GPS TEC maps during a super geomagnetic storm on Nov. 20, 2003. Firstly, the digisonde ionogram only contained echoes for scanning frequencies from 6.2MHz to 9.3MHz. The lack of echoes at frequencies below 6.2MHz is attributed to enhancements of sub-ionospheric absorption caused by precipitating RC electrons in the SED plume. Secondly, there was an obvious F1 layer, as well as an Es layer, appearing on the ISR profile, that was not observed by the digisonde due to strong sub-ionospheric absorption. For echoes at frequencies from 6.2MHz to 9.3MHz, a comparison of the virtual height obtained from the digisonde ionogram and that derived from the ISR electron density profile, demonstrated that an Es layer appeared with a peak altitude of 123km. The occurrence of the Es layer is attributed to enhancements of precipitating energetic ion fluxes in the SED plume. Our result suggests that the ionospheric behavior in the SED plume is controlled not only by ionospheric dynamical process but also by precipitating energetic RC ions/ electrons as a consequence of wave–particle interactions in the plasmaspheric plume.

Revisiting the role of magnetic field fluctuations in nonadiabatic acceleration of ions during dipolarization

Using energetic (9–212 keV/e) ion flux data obtained by the Geotail spacecraft, Ono et al. (2009) statistically examined changes in the energy density of H+ and O+ ions in the near‐Earth plasma sheet during substorm‐associated dipolarization. They found that ions are nonadiabatically accelerated by the electric field induced by the magnetic field fluctuations whose frequencies are close to their gyrofrequencies. The present paper revisits this result and finds it still holds.

Energetic ions near the dayside magnetopause reconnection site: Implications for energization sources

During a magnetopause crossing by the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft, signatures of magnetic reconnection and of accelerated flows were observed. The maximum magnetic shear model of the reconnection X-line suggests that the spacecraft passed very close to the reconnection line. At the inner edge of the low latitude boundary layer (LLBL), accelerated ions are observed, which are magnetically connected to the quasi-parallel bow shock and travel towards the northern cusp region. However, a short time later the THEMIS satellite crossed the reconnection line, onto field lines, which map out to the quasi-perpendicular bow shock (or, the weak quasi-parallel bow shock very far downstream). At these times there is no significant difference in the energetic ion flux component observed coming from the shock versus from the cusp. These signatures suggest that, at least in some cases, energetic particles observed in the cusp regions originate at the quasi-parallel bow shock.

Investigating the relationship between cusp energetic particle events and cusp diamagnetic cavities

The magnetospheric cusps in the high latitude magnetosphere are characterized by open field lines and precipitating magnetosheath ions. Contrary to the well-understood precipitating thermal magnetosheath ion population, the origins of energetic ions in the cusp regions are still a matter of controversy. It has been suggested that these cusp energetic particles (CEP) with significant fluxes up to several hundred keV/e are accelerated in the cusp by local magnetic turbulence in strongly depressed magnetic field regions called cusp diamagnetic cavities (CDC). Alternative explanations for these CEP events suggest the magnetosphere and also the quasi-parallel bow shock from where energetic ions are transported downstream and enter the cusp along newly reconnected field lines. Composition and energy spectra of these CEPs resemble those of bow shock energetic diffuse ions and support this model.In this study we investigate the relationship between CEP events and CDCs. The survey contains 822 high altitude cusp crossings observed by the TIMAS instrument on the Polar spacecraft for which we document local magnetic field conditions and the flux of energetic ions at 102keV and 191keV. We find that high fluxes of energetic ions are independent of the local magnetic field conditions. This lack of correlation between CEP and CDCs suggests that the source of these energetic ions is not local acceleration in the cusp.

Fast ion power loads on ITER first wall structures in the presence of NTMs and microturbulence

The level and distribution of the wall power flux of energetic ions in ITER have to be known accurately in order to ensure the integrity of the first wall. Until now, most quantitative estimates have been based on the assumption that fast ion transport is dictated by neoclassical effects only. However, in ITER, the fast ion distribution is likely to be affected by various MHD effects and probably also by microturbulence. We have now upgraded our orbit-following Monte Carlo code ASCOT so that it has simple, theory-based models for neoclassical tearing mode (NTM)-type islands as well as for turbulent diffusion. ASCOT also allows for full-orbit following, which is important close to the material surfaces and, possibly, also when strong toroidal inhomogeneities are present in the magnetic field. Here we introduce the new models, preliminary results obtained with them, and how these models could be made more realistic in the future. The simulations are carried out for thermonuclear alpha particles in ITER scenario 2 plasma, because we consider this combination to be most critical for the successful operation of ITER. Neither the turbulent transport nor NTM-type islands are found to introduce alarming changes in the wall loads. However, at this stage it was not possible to combine the island structures with the non-axisymmetric magnetic field of ITER, and it remains to be seen what the combined effect of drift islands together with the toroidal ripple and local field aberrations, such as those due to test blanket modules and resonant magnetic perturbations will be.

THEMIS observations of double-onset substorms and their association with IMF variations

Abstract. On 16 July 2008, two pairs of consecutive bursts of Pi2 pulsations were recorded simultaneously across the THEMIS ground-based observatory system. Wavelet transformation reveals that for each high-latitude pair, the dominant frequency of the first burst is higher than that of the second. But at low latitudes, the dominant frequency does not change. It is suggested that both pairs result from fast magnetospheric cavity waves with the second burst also containing shear Alfvén waves. INTERMAGNET magnetograms at auroral latitudes showed magnetic variations affected by two recurrent electrojets for each pair. The ground-based magnetometers and those at geostationary orbit sensed magnetic perturbations consistent with the formation of the substorm current wedge. Four consecutive enhancements of energetic electron and ion fluxes detected by the THEMIS probes in the dayside magnetosphere appeared in the later afternoon and then in the early afternoon. The horizontal magnetic variation vectors had vortex patterns similar to those induced by the upward and downward field-aligned currents during substorm times. The hodogram at mid-L stations had a polarization pattern similar to the one induced by the substorm current wedge for each Pi2 burst. The mapping of ground Pi2 onset timing to the interplanetary magnetic field (IMF) observations shows that they appear under two cycles of north-to-south and then north variation. CLUSTER 4 in the south lobe observed wave-like magnetic fluctuations, probably driven by near-Earth reconnection, similar to those on the ground. These two observations are consistent with the link of double-onset substorms to magnetotail reconnection externally triggered by IMF variations.

Research Spotlight: Wave‐particle interactions important in radiation belt dynamics

In the Earth's outer radiation belt the flux of energetic electrons and ions can vary significantly over short time periods in response to solar activity. These energetic particles can damage satellites, making it important to be able to understand and predict variability in the radiation belts. In recent years, scientists' understanding of how electrons are accelerated in the radiation belts has changed. Thorne reviews a variety of recent advances in understanding and modeling radiation belt dynamics, highlighting the importance of interactions of energetic particles with magnetosphere waves.

Low temperature Ti-Si-C thin film deposition by ion beam assisted methods

Thin, multiphase Ti-Si-C coatings were formed by IBSD or by IBAD methods on AISI 316L steel substrates in room temperature, using single Ti3SiC2 target. In those methods the TiXSiCY coatings were formed from the flux of energetic atoms and ions obtained by ion sputtering of the Ti3SiC2 compound sample. As sputtering beam the beam of Ar+ ions at energy of 15keV was applied. In the IBAD method the dynamically formed coatings were additionally bombarded by beam of Ar+ ions at energy of 15keV. The ion beams parameters were obtained by using Monte Carlo computer simulations. The morphology (SEM, TEM), chemical (EDS/EDX) and phase composition (XRD) examinations of formed coatings were provided as well as confocal Raman microspectroscopy. Analyzed coatings were relatively thin (150nm-1μm), flat and dense. XRD analysis indicated in amorphous TiSi, the traces of Ti5Si3 and other phases from Ti-Si-C system (TiSi, TiSi2,Ti3SiC2). For chemical bonds investigation, the laser beam with length of 532nm was used. Those analyses were performed in the low (LR) or in high (HR) resolution modes in room temperature and in 4000C. In the HR mode the spectral resolution was close to 2 cm−1. In Raman spectra peaks at: 152cm−1, 216cm−1, 278cm−1, 311 cm−1, 608cm−1, 691cm−1 were recorded. Nanoindentation tests were done on coated and uncoated substrates with diamond, Berkovich-type indenter. Vickers hardness HIT and reduced elastic modulus EIT were calculated using Olivier& Pharr method. HIT for coated substrates was in the range 2.7 to 5.3 GPa, EIT was 160 GPa.

Nanocrystalline Silicon Thin Films Fabricated at 80°C by Using Electron Cyclotron Resonance Chemical Vapor Deposition

Deposition of nanocrystalline silicon (nc-Si) on glass at very low temperatures by electron cyclotron resonance (ECR) plasma enhanced chemical vapour deposition (PECVD) was investigated. It was shown that nc-Si could be deposited from hydrogen diluted silane gas at a substrate temperature of 80° C with a crystalline fraction up to 80% and a lateral grain size of around 50 nm. This was achieved by growing the nc-Si in a low pressure regime which ensured that mono-silyl species were the dominant deposition precursor. Furthermore, a high flux of energetic hydrogen ions was required to induce crystallisation of the silicon material through a chemical annealing process.

Fluorine Plasma Treatments of Poly(propylene) Films, 2 – Modeling Reaction Mechanisms and Scaling

AbstractThe surface properties of commodity hydrocarbon polymers such as poly(propylene) (PP) can be modified by functionalization with plasma‐generated radicals and ions. For example, affixing fluorine to a hydrocarbon surface lowers surface energy and increases hydrophobicity. One such process is treatment of PP films in low‐pressure, capacitively coupled plasmas (CCPs) sustained in F2‐containing gas mixtures. F atoms produced in the plasma abstract H atoms from the hydrocarbon and passivate the resulting alkyl sites producing CFn sites. Energetic ion and photon fluxes sputter and initiate crosslinking. In this paper, the plasma fluorination of PP in a CCP sustained in Ar/F2 is discussed with results from a two‐dimensional plasma hydrodynamics model. The surface reaction mechanism includes a hierarchy of H abstraction and F/F2 passivation reactions, as well as crosslinking, and ion and photon‐activated processes. Predictions for surface composition were compared to experiments. We found that the lack of total fluorination with long plasma exposure is likely caused by crosslinking, which creates CC bonds that might otherwise be passivated by F atoms. Increasing steric hindrances as fluorination proceeds also contribute to lower F/C ratios.magnified image

Efficient acceleration of a small dense plasma pellet by consecutive action of multiple short intense laser pulses

AbstractThe acceleration of a micrometer-sized plasma pellet at 100 critical densities (1023 cm−3) by consecutive application of ultra-short ultra-intense laser pulses is studied using two-dimensional particle-in-cell simulation. It is shown that due to the repeated actions of the laser ponderomotive force, a small dense plasma pellet can be efficiently accelerated, with a considerable fraction of the plasma ions accelerated to high speeds. The proposed scheme can provide a high-density flux of energetic ions, which should be valuable in many practical applications.

A simulation study of particle energization observed by THEMIS spacecraft during a substorm

Energetic ions with hundreds of keV energy are frequently observed in the near‐Earth tail during magnetospheric substorms. We examined the sources and acceleration of ions during a magnetospheric substorm on 1 March 2008 by using Time History of Events and Macroscale Interactions during Substorms (THEMIS) and Cluster observations and numerical simulations. Four of the THEMIS spacecraft were aligned at yGSM = 6 RE during a very large substorm (AE = 1200) while the Cluster spacecraft were located about 5 RE above the auroral ionosphere. For 2 h before the substorm, Cluster observed ionospheric oxygen flowing out into the magnetosphere. After substorm onset the THEMIS P3 and P4 spacecraft located in the near‐Earth tail (xGSM = −9 RE and −8 RE, respectively) observed large fluxes of energetic ions up to 500 keV. We used calculations of millions of ions of solar wind and ionospheric origin in the time‐dependent electric and magnetic fields from a global magnetohydrodynamic simulation of this event to study the source of these ions and their acceleration. The simulation did a good job of reproducing the particle observations. Both solar wind protons and ionospheric oxygen were accelerated by nonadiabatic motion across large (&gt;∼5 mV/m) total electric fields (both potential and induced). The acceleration occurred in the “wall” region of the near‐Earth tail where nonadiabatic motion dominates over convection and the particles move rapidly across the tail. The acceleration occurred mostly in regions with large electric fields and nonadiabatic motion. There was relatively little acceleration in regions with large electric fields and adiabatic motion or small electric fields and nonadiabatic motion. Prior to substorm onset, ionospheric ions were a significant contributor to the cross‐tail current, but after onset, solar wind ions become more dominant.