Ion Temperature Enhancements Research Articles

Mechanism of enhanced ion temperature by impurity seeding in EAST H-mode plasma

Ion temperature (T i) profiles are commonly observed to increase in peaking, leading to higher central T i, after impurity seeding in the EAST H-mode plasma. Argon can be more efficient at raising T i than neon. Toroidal rotation can also be enhanced in scenarios with NBI heating. A more significant increase in toroidal rotation is brought about by seeding argon than seeding neon. Turbulence is experimentally observed to be suppressed. Extensive modeling using the quasilinear gyrokinetic code QuaLiKiz is performed to explain the above observations. It is found that the enhanced T i can always be explained by the turbulence stabilization. However, the mechanism of turbulence stabilization is related to heating methods and the seeding impurity species. In the pure RF (ECRH + LHW) heating scenarios, where only the trapped electron mode (TEM) exists, argon can stabilize the TEM more significantly than neon due to its higher charge and heavier mass. In scenarios with increasing NBI power, the ion heat flux can be dominated by the ion temperature gradient (ITG), thus the enhanced T i is mainly attributed to ITG stabilization. In these cases, except argon’s ability to more efficiently stabilize TEM, more evident increased toroidal rotation brought about by argon seeding can also be beneficial to stabilize turbulence.

Behaviors of Ionospheric Topside Ion Density, Ion Temperature, and Electron Temperature During the 20 November 2003 Superstorm

AbstractWe identified a few new storm‐time ionospheric phenomena by analyzing disturbances in topside ion density, electron temperature, and ion temperature at ∼840 km altitude measured by the Defense Meteorological Satellite Program satellites during the 20 November 2003 magnetic storm. The storm‐time ion density enhancements showed different features at different local times. Longitudinal structures in the enhanced ion density occurred in the morning sector and extended from equatorial regions to middle latitudes. Ion density increase due to enhanced fountain effect was observed in the evening sector and lasted for ∼18 hr. A positive ionospheric storm occurred during the late recovery phase of the storm and was associated with increased atomic oxygen to molecular nitrogen column density ratio. Electron temperature at subauroral latitudes reached 8000 K during the storm, ∼4000 K higher than the quiet‐time temperature. The subauroral temperature enhancement lasted for 2–3 days. Simultaneous enhancements in the ion density, electron temperature, and ion temperature from subauroral to equatorial latitudes occurred in the night‐time ionosphere and lasted for ∼18 hr. A negative correlation between ion density and electron/ion temperature variations occurred in the dusk sector for ∼12 hr. An enhanced ion temperature crest in the winter hemisphere during the magnetic storm lasted for 2 days. A decrease in the ion temperature crest was also observed with an increase of the ion density. These new features in the ionospheric density and temperature, together with the results from previous studies, provide a more comprehensive scenario of the ionospheric response to the superstorm.

Ion Heating in the Polar Cap Under Northwards IMF Bz

AbstractJoule heating deposits a significant amount of energy into the high‐latitude ionosphere and is an important factor in many magnetosphere‐ionosphere‐thermosphere coupling processes. We consider the relationship between localized temperature enhancements in polar cap measured with the Resolute Bay Incoherent Scatter Radar‐North (RISR‐N) and the orientation of the interplanetary magnetic field (IMF). Based on analysis of 10 years of data, RISR‐N most commonly observes ion heating in the noon sector under northwards IMF . We interpret heating events in that sector as being primarily driven by sunwards plasma convection associated with lobe reconnection. We attempt to model two of the observed temperature enhancements with a data‐driven first principles model of ionospheric plasma transport and dynamics, but fail to fully reproduce the ion temperature enhancements. However, evaluating the ion energy equation using the locally measured ion velocities reproduces the observed ion temperature enhancements. This result indicates that current techniques for estimating global plasma convection pattern are not adequately capturing mesoscale flows in the polar cap, and this can result in underestimation of the energy deposition into the ionosphere and thermosphere.

Ion Scattering and Energization in Filamentary Structures Through Earth's Magnetosheath

AbstractMulti‐point measurements on kinetic scales through Earth's magnetosheath have revealed a spectrum of filamentary currents and vortical flows advected with the shocked plasmas outside the magnetopause. The spectral energy density in these structures is correlated with enhanced ion temperatures. Using an empirically derived statistical model based on fluid‐kinetic theory for these structures we demonstrate how they act to scatter magnetosheath ions. Through the combined action of energization in the direction perpendicular to the background magnetic field along chaotic orbits, and pitch‐angle scattering into the parallel direction appreciable ion energization occurs. These dynamics drive heating while generating non‐thermal energetic tails similar to that observed. It is shown how the operation of this process depends on the field topology with deviations from planar form and counter‐propagation required to drive significant energization. This process will modulate ion anisotropies through the magnetosheath independent of both adiabatic effects and the action of anisotropy instabilities.

Anomalous Electron Temperature Increases in the Evening Equatorial Ionosphere

AbstractWe use novel radar observations at the Jicamarca Radio Observatory to study the first observations of highly enhanced plasma temperatures in the evening equatorial ionosphere. These short‐lived solstice evening events occurred following large upward plasma drifts and sharply reduced plasma densities. The electron temperatures increase during the August 5 and 6, 2011 moderate solar event reached peak values of about 1,000 K near 350 km. Smaller electron temperature increases were observed to altitudes up to about 500 km. There were also smaller concurrent ion temperature enhancements. During the very low solar flux January 20 and 21, 2020 event, a peak electron temperature increase of about 700 K occurred at an altitude of about 270 km. We also show that SAMI2‐PE simulations using the measured vertical plasma drifts reproduce the main characteristics of the measured plasma densities and temperatures up to 300 km, but not at higher altitudes. These simulations indicate that the evening anomalous plasma heating below about 300 km is due to the decrease in the electron‐ion cooling rate resulting from upward plasma drift driven decrease in the plasma density. Plasma transport and reduced cooling rate is a potential source of higher altitude heating.

Electron Density Depletion Region Observed in the Polar Cap Ionosphere

AbstractThis paper presents and discusses electron density depletion regions observed with the incoherent scatter EISCAT Svalbard Radar (ESR) located at 75.43°N geomagnetic latitude. The data include several decades of measurements, which make them suitable for studying statistical features and characteristics of the ionospheric parameters. Here we focus on the electron density depletions and their dependence on diurnal and seasonal variations and solar activity. An electron density depletion region is identified in the ESR data in the early morning sector. This depletion region seems to be clearest during equinox and winter and moderate/high solar activity. An enhancement in the ion temperature is often co‐located with the electron density depletion region. The ion temperature enhancement could indicate that ion frictional heating is related to the electron density depletion region. However, during summer when the solar activity is low, the electron density depletion is not observed although the ion temperature is enhanced, suggesting that formation of the electron density depletion regions due to ion frictional heating may depend on the background effective temperature and O/N2 ratio. In addition, seasonal changes in the solar zenith angle could also contribute to the formation of the depletion region.

A Statistical Study of the Subauroral Polarization Stream Over North American Sector Using the Millstone Hill Incoherent Scatter Radar 1979–2019 Measurements

AbstractThis work conducts a statistical study of the subauroral polarization stream (SAPS) feature in the North American sector using Millstone Hill incoherent scatter radar measurements from 1979 to 2019, which provides a comprehensive SAPS climatology using a significantly larger database of radar observations than was used in seminal earlier works. Key features of SAPS and associated electron density (Ne), ion temperature (Ti), and electron temperature (Te) are investigated using a superposed epoch analysis method. The characteristics of these parameters are investigated with respect to magnetic local time, season, geomagnetic activity, solar activity, and interplanetary magnetic field (IMF) orientation, respectively. The main results are as follows: (1) Conditions for SAPS are more favorable for dusk than near midnight, for winter compared to summer, for active geomagnetic periods compared to quiet time, for solar minimum compared to solar maximum, and for IMF conditions with negative By and negative Bz. (2) SAPS is usually associated with a midlatitude trough of 15–20% depletion in the background density. The SAPS‐related trough is more pronounced in the postmidnight sector and near the equinoxes. (3) Subauroral ion and electron temperatures exhibit a 3–8% (50–120 K) enhancement in SAPS regions, which tend to have higher percentage enhancement during geomagnetically active periods and at midnight. Ion temperature enhancements are more favored during low solar activity periods, while the electron temperature enhancement remains almost constant as a function of the solar cycle. (4) The electron thermal content, Te × Ne, in the SAPS associated region is strongly dependent on 1/Ne, with Te exhibiting a negative correlation with respect to Ne.

Force and Energy Balance of the Dipolarization Front

AbstractWe have performed a particle‐in‐cell simulation to understand the dynamic evolution of the dipolarization front during its early stage after ejected by magnetic reconnection, focusing on the force and energy balance around the dipolarization front. We track the temporal evolution of the force and different energy channels in the Lagrangian frame of the dipolarization front. We find that the curvature force continuously accelerates the dipolarization front moving outward, while the thermal pressure gradient force hinders the movement of the DF. The DF is accelerated outward because the total force is positive. The maximum value of Bz at the DF gradually increases during the outward propagation of the front. Although the dipolarization front is the site with significant energy conversion from the magnetic field to plasma, that is, J · E > 0, the compression of the magnetic field by the convergent flow at the front leads to the gradual enhancement of Bz. The released magnetic energy bulk accelerates and heats the plasma. The plasma thermal energy increases at the front that is primarily due to the work of the pressure gradient (v · (∇ · P) > 0), while the enthalpy flux emitted from the front reduces the thermal energy. Both the pressure‐strain interaction −(P′ · ∇) · v and the pressure dilation p∇ · v contribute to the ion and electron temperature enhancement. Our results are important for revealing the dynamic evolution of the dipolarization fronts and will aid us to understand the energy transport in the disturbed magnetotail.

Plasma Cavity Formation During Ionospheric Heating at Arecibo

AbstractThe formation of an anomalous, high‐altitude plasma cavity was observed during the 11–15 June 2019 ionospheric heating campaign at Arecibo Observatory. The cavity was induced by interactions of the transmitted 5.125‐MHz heater wave with the ionospheric plasma. Simultaneous ion line and plasma line measurements were taken by the Arecibo Incoherent Scatter Radar (ISR). We used a novel experimental technique, enabling rapid pulsing of the heater, to collect ISR spectral data of the heated ionosphere without high frequency (HF)‐induced enhanced ion line (HFIL), simplifying the analysis. ISR data were analyzed using Tikhonov regularization, revealing that the cavity was confined to a very narrow altitude range around 350 km and constituted a deep depletion of the electron density, along with strong electron temperature enhancement, and ion temperature enhancement. We report on the details of these observations, and the possibility for unique combinations of physical interactions to explain the underlying mechanisms.

Neutron yield enhancement and suppression by magnetization in laser-driven cylindrical implosions

In inertial confinement fusion, an externally applied magnetic field can reduce heat losses in the compressing fuel thereby increasing neutron-averaged ion temperatures and neutron yields. However, magnetization is only beneficial if the magnetic pressure remains negligible compared to the fuel pressure. Experiments and three-dimensional magneto-hydrodynamic simulations of cylindrical implosions on the OMEGA laser show ion temperature and neutron yield enhancements of up to 44% and 67%, respectively. As the applied axial magnetic field is increased to nearly 30 T, both experiments and simulations show yield degradation. For magnetized, cylindrical implosions, there exists an optimal magnetic field that maximizes the increase in yield. Limiting the fuel convergence ratio by preheating the fuel can further increase the benefit of magnetization. The results demonstrate that it is possible to create a plasma with a density of order 1 g/cm3 and an ion temperature greater than 1 keV with a magnetic pressure comparable to the thermal pressure, a new regime for laser-produced plasmas on OMEGA.

Plasma Flow in the North‐South Aligned Discrete Aurora Equatorward of the Cusp

AbstractOn the equatorward side of the dayside cusp there often appear diffuse auroras. In this paper, we report north‐south aligned discrete aurora events and show the spatial relationships between the auroras and the plasma flow. Several events of the north‐south aligned discrete auroral structures were identified using an all‐sky imager at Longyearbyen, Svalbard, during the recovery of a moderately disturbed period on 8 December 2013. During a brief interval of the moderately disturbed period, the cusp shifted to higher latitudes; as a result, the field‐aligned beam of the EISCAT Svalbard Radar (ESR) passed through the northern portion of the north‐south aligned auroral structures. Simultaneous observations from the all‐sky imager and ESR reveal that enhancements in ion temperature (caused by fast ion flow) occurred near the eastward and westward boundaries of the north‐south aligned auroral structures. However, within the region of the most enhanced aurora, the ion temperature enhancements were moderately suppressed. These features indicate that the ion flow slows down in the region of electron precipitation responsible for north‐south aligned auroral structures. We can quantitatively interpret the slowdown of the flow as the reduction of the electric field due to the polarization effect in the north‐south aligned region of the increased Pedersen conductivity. It thus appears that the magnetospheric source of the north‐south aligned discrete auroras is a limited area embedded in the region of plasma flow toward the dayside magnetopause.

Characteristics of CME‐ and CIR‐Driven Ion Upflows in the Polar Ionosphere

AbstractWe investigated how velocity and flux of ionospheric ion upflows vary during magnetic storms driven by corotating interaction regions (CIRs) and coronal mass ejections (CMEs), using data from the European Incoherent Scatter (EISCAT) Tromsø UHF and Svalbard radars between 1996 and 2015. The characteristics of ion upflows were compared with ion and electron temperature variations measured with the EISCAT radars and also joule heating rate, electric field, and field‐aligned current distribution derived from the Weimer model. Upward ion velocity increases in the nighttime at Tromsø (66.2 °N geomagnetic latitude) just after the CIR‐ and CME‐driven storms, corresponding to electron temperature enhancements due to soft particle precipitation and also ion temperature enhancements in the strong westward electric field region. The CME‐driven storms have larger upward ion flux (~1.7 × 1013 m−2s−1) than those under the CIR‐driven storms (~0.3 × 1013 m−2s−1). In the daytime, ion upflows are seen at Longyearbyen, Svalbard (75.2 °N geomagnetic latitude), with an upward flux of typically 1013 m−2s−1 for small CIR and CME storm cases. Substantial ion upflows last for a few days after the storm onsets under small CIR storms, whereas they last for only a day under small CME storms. Under both the cases, the substantial ion upflows are associated with an enhancement of the Region 1 field‐aligned current, eastward electric field and Joule heating rate. For large CME storms, substantial ion upflows are absent in the daytime probably due to equatorward expansion of the auroral oval.

High‐Resolution Local Measurements of F Region Ion Temperatures and Joule Heating Rates Using SuperDARN and Ground‐Based Optics

AbstractFrictional heating, frequently termed Joule heating, results from the difference in ion and neutral flows in the Earth's upper atmosphere and is a major energy sink for the coupled magnetosphere‐ionosphere‐thermosphere system. During disturbed geomagnetic conditions, energy input from the Earth's magnetosphere can strongly enhance ion velocities and densities, which will generally increase the rate of Joule heating. Previous theoretical and experimental studies have shown that small‐scale variations in Joule heating can be quite significant in the overall energy budget. In this study, we employ high‐resolution fitting of ion velocities obtained by Super Dual Auroral Radar Network (SuperDARN) coherent scatter, along with spatially resolved neutral wind data from the Poker Flat Scanning Doppler Imager, to examine the spatial and temporal structure of F region ion temperature enhancements, as well as changes in Joule heating rates due to the neutral wind. These results are compared to those obtained using Poker Flat Incoherent Scatter Radar in order to assess the validity of this analysis, with the objective of developing a method that can be applied to any current or future neutral measurements worldwide, thanks to the global coverage of SuperDARN. We examine the agreement between the ion temperatures predicted using the Scanning Doppler Imager‐SuperDARN method and the temperatures measured directly by Poker Flat Incoherent Scatter Radar and discuss possible reasons for any discrepancies. We observe significant spatial structure in both the ion temperature and Joule heating rates during periods of magnetic activity.

Swarm Satellite and EISCAT Radar Observations of a Plasma Flow Channel in the Auroral Oval Near Magnetic Midnight

AbstractWe present Swarm satellite and EISCAT radar observations of electrodynamical parameters in the midnight sector at high latitudes. The most striking feature is a plasma flow channel located equatorward of the polar cap boundary within the dawn convection cell. The flow channel is 1.5° wide in latitude and contains southward electric field of 150 mV/m, corresponding to eastward plasma velocities of 3,300 m/s in the F‐region ionosphere. The theoretically computed ion temperature enhancement produced by the observed ion velocity is in accordance with the measured one by the EISCAT radar. The total width of the auroral oval is about 10° in latitude. While the poleward part is electric field dominant with low conductivity and the flow channel, the equatorward part is conductivity dominant with at least five auroral arcs. The main part of the westward electrojet flows in the conductivity dominant part, but it extends to the electric field dominant part. According to Kamide and Kokubun (1996), the whole midnight sector westward electrojet is expected to be conductivity dominant, so the studied event challenges the traditional view. The flow channel is observed after substorm onset. We suggest that the observed flow channel, which is associated with a 13‐kV horizontal potential difference, accommodates increased nightside plasma flows during the substorm expansion phase as a result of reconnection in the near‐Earth magnetotail.

Ion Heating in the Martian Ionosphere

AbstractEnergetic O+ and O ions with energies of up to a few hundred eV are observed in the Martian ionosphere. Corresponding ion velocity distributions show ion conics, suggesting that the observed ion populations have been heated perpendicular to the local magnetic field before experiencing a magnetic mirror force. Magnetic field observations support these interpretations: wave power at the local O+ and O gyrofrequencies in the spacecraft frame is observed coincident with the energetic ions, within an apparent magnetic field bottle‐like topology. Analysis of the observed ion conics leads to estimates of ion temperatures of 10–30 eV. We suggest that the ion populations are initially heated perpendicular to the local magnetic field by wave power propagating inward from the Mars‐solar wind interaction. The local magnetic field “balloons out” in response to these enhanced ion temperatures and pressures. The resultant magnetic field topology is bottle like; the transversely heated ions would subsequently experience a magnetic mirror force in the converging field regions, agreeing with the reported observations. Such strong heating events that significantly increase the ion temperature and pressure, thereby decreasing the net magnetic field, are rare and seem to occur under specific interplanetary magnetic field orientations. Events were observed to span the upper exobase region and just above, a region characterized by significant ion densities in an increasingly collisionless domain. Ion heating in this region has the potential to drive significant ion outflows, thus contributing to atmospheric loss from the planet.

Simultaneous observations of traveling convection vortices: Ionosphere‐thermosphere coupling

AbstractWe present simultaneous observations of magnetosphere‐ionosphere‐thermosphere coupling over Svalbard during a traveling convection vortex (TCV) event. Various spaceborne and ground‐based instruments made coordinated measurements, including magnetometers, particle detectors, an all‐sky camera, European Incoherent Scatter (EISCAT) Svalbard Radar, Super Dual Auroral Radar Network (SuperDARN), and SCANning Doppler Imager (SCANDI). The instruments recorded TCVs associated with a sudden change in solar wind dynamic pressure. The data display typical features of TCVs including vortical ionospheric convection patterns seen by the ground magnetometers and SuperDARN radars and auroral precipitation near the cusp observed by the all‐sky camera. Simultaneously, electron and ion temperature enhancements with corresponding density increase from soft precipitation are also observed by the EISCAT Svalbard Radar. The ground magnetometers also detected electromagnetic ion cyclotron waves at the approximate time of the TCV arrival. This implies that they were generated by a temperature anisotropy resulting from a compression on the dayside magnetosphere. SCANDI data show a divergence in thermospheric winds during the TCVs, presumably due to thermospheric heating associated with the current closure linked to a field‐aligned current system generated by the TCVs. We conclude that solar wind pressure impulse‐related transient phenomena can affect even the upper atmospheric dynamics via current systems established by a magnetosphere‐ionosphere‐thermosphere coupling process.

Electrodynamic structure of the morning high‐latitude trough region

AbstractWe describe the electrodynamics of a postmidnight, high‐latitude ionospheric trough, observed with the European Incoherent Scatter radar in northern Scandinavia on 24–25 June 2003 around 22:00–02:30 UT during quiet conditions. The UHF radar made meridian scans with a 30 min cadence resulting in nine cross sections of ionospheric parameters. The F region electric field was also determined with the tristatic system. Ionospheric equivalent currents, calculated from ground magnetometer data, mostly show an electrojet‐like current that is reasonably uniform in the longitudinal direction. Combined analysis of the conductances and equivalent current with a local Kamide‐Richmond‐Matsushita (KRM) method yields the ionospheric electric field and field‐aligned current (FAC) in a 2‐D (latitude‐longitude) area around the radar. We conclude that the most likely scenario is one where the trough is initially created poleward of the auroral oval by downward FAC that evacuates the F region, but as the trough moves to lower latitudes during the early morning hours, it becomes colocated with the westward electrojet. There the electron density further decreases due to increased recombination caused by enhanced ion temperature, which in turn is brought about by a larger convection speed. Later in the morning the convection speed decreases and the trough is filled by increasing photoionization.

Incoherent scatter ion line enhancements and auroral arc-induced Kelvin–Helmholtz turbulence

We present two cases of incoherent-scatter ion line enhancements in conjunction with auroral arcs drifting through the radar beam. The up- and downshifted ion line shoulders as well as the spectral region between them are enhanced equally and simultaneously. The power enhancements are one order of magnitude above the thermal level and are concentrated in less than 15km wide altitude ranges at the ionospheric F region peak. The auroral arc passages are preceded by significantly enhanced ion temperatures in the E region, assumed to be caused by transient electric fields associated with velocity shears. We use a Hall MHD model of velocity shears perpendicular to the geomagnetic field and show that a Kelvin–Helmholtz instability will grow for the two presented cases.

Decrease in sodium density observed during auroral particle precipitation over Tromsø, Norway

Using a simultaneous and common‐volume observation by a European incoherent scatter (EISCAT) VHF radar and a sodium lidar at Tromsø, Norway (69.6°N, 19.2°E), we have determined, for the first time, the effect of pure particle precipitation, excluding that of the electric field, on sodium density variations. Our observation on 24–25 January 2012 showed that sodium atom density decreased when there was no ion temperature enhancement (indicating a weak electric field) and the electron density increased (indicating strong particle precipitation). From the results, we have concluded that auroral particle precipitation induced sodium atom density decrease in this event. Furthermore, a discussion is provided regarding the time response of the decrease in sodium density.

Ion–neutral coupling in Earth's thermosphere, estimated from concurrent radar and optical observations above Alaska

During March–April 2011 a campaign of coordinated observations was undertaken between the Poker Flat Advanced Modular Incoherent Scatter Radar and the Poker Flat Scanning Doppler Imager. These instruments provide horizontally resolved maps of plasma and neutral parameters in Earth's thermosphere. We report on data collected during the campaign, and use these data to investigate two key aspects of ion–neutral coupling, namely Joule heating and the ion–neutral collision frequency. Volumetric Joule heating rates were often well correlated with measured ion temperature enhancements. The contribution of the neutral wind dynamo to the observed heating rates was positive when the absolute horizontal magnetic field perturbation (|ΔH|) was less than approximately 40nT, and negative above that level. The total momentum–transfer ion–neutral collision frequency was estimated to be 1.02−0.152+0.179s−1 at an altitude of 260km, which, for a neutral composition of 75% atomic oxygen, yielded an estimate of the O+–O collision frequency of 0.766−0.114+0.134s−1.