In this study we examine the ability of protons of solar origin to access the near‐equatorial inner magnetosphere. Here we examine four distinct solar proton events from 20–200 MeV, concurrent with ...both quiet time and storm time conditions using proton data from the ACE satellite in the solar wind upstream of Earth and data from the Relativistic Electron Proton Telescope (REPT) instrument aboard Van Allen Probes. We examine the direct flux correspondence between interplanetary space and the inner magnetosphere. Small substructures in interplanetary space are observable in the REPT flux profiles, which can penetrate down to L values of ≤4. Furthermore, there are orbit‐to‐orbit variations in the west‐to‐east anisotropic flux ratios. The anisotropic flux ratios are used as a proxy for cutoff energies and display cutoff variations with L shell and energy. The dependence of the anisotropic flux ratio on Dst values is shown. The results paint a picture of highly dynamic spatial and temporal proton cutoff rigidities in the near‐equatorial inner magnetosphere.
Key Points
Small flux substructures in interplanetary space are observed in the inner magnetosphere
West‐to‐east flux ratios are used as a proxy for cutoff location and energy
West‐to‐east flux ratios are highly dynamic from orbit to orbit and respond quickly to magnetospheric changes
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Magnetic reconnection is a universal process where energy is transferred from magnetic fields to particles. However, it remains unclear whether this transfer of energy includes the direct ...energization of particles to high energies (i.e., >10s of keV). We compare the spectral indices of energetic (50–200 keV) electrons from six magnetotail electron diffusion region candidates encountered by MMS with those from “quiet‐time” plasma sheet crossings to test whether energetic electron enhancements result from direct energization at/near the reconnection site or simply focusing high‐energy populations that do not originate from the nearby X‐line and already exist in the plasma sheet along the newly reconnected field lines. The study suggests that active reconnection can be a source of localized electron energization. However, the EDR spectra are not outside the range of those from the quiet‐time plasma sheet, which surprisingly still often have very energetic (up to and beyond 200 keV) electrons present.
Plain Language Summary
Magnetic reconnection is a fundamental process in plasma physics and is hypothesized to be an efficient process to accelerate particles up to very high energies by transferring energy held in the magnetic field to the particles. Similar to how a taught rubber band can snap, releasing its latent energy—so too do magnetic fields “snap” in reconnection; as the field lines relax to their normal state, they transfer their energy to particle. This paper addresses an outstanding question of whether magnetic reconnection in fact produces high energy electrons. While many computer simulations have predicted this, most in situ observations have focused on energization at much lower energies than we look at here. However, this paper compares a handful of events very near the region where reconnection is believed to occur to a “control group” of nonactive regions not near a reconnection site and finds that the events nearest the reconnection do tend to have more energetic electrons. This provides evidence that the energetic electrons are in fact coming from the reconnection site.
Key Points
Six candidate EDRs identified by the MMS team are compared to a statistical database of quiet‐time plasmasheet crossings
The spectral indices of energetic electrons near the EDRs are indeed harder than the plasmasheet crossings, suggesting local energization
Even the quiet‐time plasmasheet crossings include cases with surprisingly hard spectra, perhaps sourced by distant tail reconnection
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The first cosmic ray albedo proton map of the Moon Wilson, Jody K.; Spence, Harlan E.; Kasper, Justin ...
Journal of Geophysical Research: Planets,
December 2012, Volume:
117, Issue:
E12
Journal Article
Peer reviewed
Open access
Neutrons emitted from the Moon are produced by the impact of galactic cosmic rays (GCRs) within the regolith. GCRs are high‐energy particles capable of smashing atomic nuclei in the lunar regolith ...and producing a shower of energetic protons, neutrons and other subatomic particles. Secondary particles that are ejected out of the regolith become “albedo” particles. The neutron albedo has been used to study the hydrogen content of the lunar regolith, which motivates our study of albedo protons. In principle, the albedo protons should vary as a function of the input GCR source and possibly as a result of surface composition and properties. During the LRO mission, the total detection rate of albedo protons between 60 MeV and 150 MeV has been declining since 2009 in parallel with the decline in the galactic cosmic ray flux, which validates the concept of an albedo proton source. On the other hand, the average yield of albedo protons has been increasing as the galactic cosmic ray spectrum has been hardening, consistent with a disproportionately stronger modulation of lower energy GCRs as solar activity increases. We construct the first map of the normalized albedo proton emission rate from the lunar surface to look for any albedo variation that correlates with surface features. The map is consistent with a spatially uniform albedo proton yield to within statistical uncertainties.
Key Points
The albedo proton yield is spatially uniform over the Moon's surface
The albedo/primary proton ratio at the Moon is within a factor of 3 of Earth's
The lunar albedo proton yield is increasing as solar activity increases
Observations from the Energetic Particle Detector (EPD) instrument suite aboard the Magnetospheric Multiscale (MMS) spacecraft show that energetic (greater than tens of keV) magnetospheric particle ...escape into the magnetosheath occurs commonly across the dayside. This includes the surprisingly frequent observation of magnetospheric electrons in the duskside magnetosheath, an unexpected result given assumptions regarding magnetic drift shadowing. The 238 events identified in the 40 keV electron energy channel during the first MMS dayside season that exhibit strongly anisotropic pitch angle distributions indicating monohemispheric field‐aligned streaming away from the magnetopause. A review of the extremely rich literature of energetic electron observations beyond the magnetopause is provided to place these new observations into historical context. Despite the extensive history of such research, these new observations provide a more comprehensive data set that includes unprecedented magnetic local time (MLT) coverage of the dayside equatorial magnetopause/magnetosheath. These data clearly highlight the common escape of energetic electrons along magnetic field lines concluded to have been reconnected across the magnetopause. While these streaming escape events agree with prior studies which show strong correlation with geomagnetic activity (suggesting a magnetotail source) and occur most frequently during periods of southward IMF, the high number of duskside events is unexpected and previously unobserved. Although the lowest electron energy channel was the focus of this study, the events reported here exhibit pitch angle anisotropies indicative of streaming up to 200 keV, which could represent the magnetopause loss of >1 MeV electrons from the outer radiation belt.
Plain Language Summary
Although extremely powerful, the Sun does not produce many energetic charged particles. However, lower energy particles originating from the Sun (and Earth) can be energized through multiple processes by the Earth's magnetic field. As such, energetic particles are primarily found within the region of space dominated by the Earth's magnetic field, known as the “magnetosphere.” Despite this fact, energetic particles are still commonly found outside of the magnetosphere. This raises questions as to where these particles come from and how they get there. The study presented here shows new observations of energetic particles (specifically focusing on electrons) from the Magnetospheric Multiscale (MMS) spacecraft. These observations show that the energetic electrons seen outside the magnetosphere are in fact coming from inside the magnetosphere and are escaping via a mechanism known as magnetic reconnection, where magnetic field lines from the Earth and Sun meet and are reconfigured. The reorientation of these field lines during reconnection provides an easy avenue of escape for energetic electrons within the magnetosphere. Although this loss process is minimal in terms of the total number of particles in the magnetosphere, it is fundamental for our understanding of the intrinsic processes of near‐Earth space.
Key Points
The 238 field‐aligned 40 keV electron streaming events are identified in MMS magnetosheath observations
Statistically, electron escape/streaming from the magnetosphere occurs across all MLT on the dayside
Results support the conclusion that these energetic electrons escape via reconnected field lines
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The Van Allen Probes mission operations materialized through a distributed model in which operational responsibility was divided between the Mission Operations Center (MOC) and separate instrument ...specific SOCs. The sole MOC handled all aspects of telemetering and receiving tasks as well as certain scientifically relevant ancillary tasks. Each instrument science team developed individual instrument specific SOCs proficient in unique capabilities in support of science data acquisition, data processing, instrument performance, and tools for the instrument team scientists. In parallel activities, project scientists took on the task of providing a significant modeling tool base usable by the instrument science teams and the larger scientific community. With a mission as complex as Van Allen Probes, scientific inquiry occurred due to constant and significant collaboration between the SOCs and in concert with the project science team. Planned cross-instrument coordinated observations resulted in critical discoveries during the seven-year mission. Instrument cross-calibration activities elucidated a more seamless set of data products. Specific topics include post-launch changes and enhancements to the SOCs, discussion of coordination activities between the SOCs, SOC specific analysis software, modeling software provided by the Van Allen Probes project, and a section on lessons learned. One of the most significant lessons learned was the importance of the original decision to implement individual team SOCs providing timely and well-documented instrument data for the NASA Van Allen Probes Mission scientists and the larger magnetospheric and radiation belt scientific community.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Successful treatment of skull base tumors with interstitial brachytherapy requires high targeting accuracy for the brachytherapy needles to avoid harming vital anatomical structures. To enable safe ...placement of the needles in this area, we developed an image-based planning and navigation system for brachytherapy, which includes a custom-made mechanical positioning arm that allows rough and fine adjustment of the needle position. The fine-adjustment mechanism consists of an XYZ microstage at the base of the arm and a needle holder with two fine-adjustable inclinations. The rotation axes of the inclinations cross at the tip of the needle so that the inclinational adjustments do not interfere with the translational adjustments. A vacuum cushion and a noninvasive fixation frame are used for the head immobilization. To avoid mechanical bending of the needles due to the weight of attached tracking markers, which would be detrimental for targeting accuracy, only a single LED marker on the tail of the needle is used. An experimental phantom-based targeting study with this setup demonstrated that a positioning accuracy of 1.4 mm (rms) can be achieved. The study showed that the proposed setup allows brachytherapy needles to be easily aligned and inserted with high targeting accuracy according to a preliminary plan. The achievable accuracy is higher than if the needles are inserted manually. The proposed system can be linked to a standard afterloader and standard dosimetry planning module. The associated additional effort is reasonable for the clinical practice and therefore the proposed procedure provides a promising tool for the safe treatment of tumors in the skull base area.
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