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In this paper, we report the rise time of three silicon reach-through avalanche photodiodes (APD) when measuring alpha particles and low-energy ions in the energy range from 50 to 300 keV. The APDs were custom manufactured by Hamamatsu Photonics and differ by their doping manufacturing method (p-type or n-type) and their depletion layer thickness (30 or $150~\mu \text{m}$ ). Our findings are summarized as follows: 1) the rise time is largely a function of detector drift layer thickness and 2) the rise time is mostly independent of ion species. The measured rise time values were comparable to ~1.5 ns for the two $30~\mu \text{m}$ APDs at the operational bias voltages. In combination with the timing electronics, such as constant fraction discriminators, a less than 1-ns response time resolution will be achievable for these APDs. These new findings are valuable for applying APDs for suprathermal particle measurements in space physics, enabling simplified time-of-flight and energy systems, and high count rate applications.

This paper reports a novel application of silicon photomultipliers (SiPMs) for directly counting kiloelectron-volt-range electrons and protons. Current instruments for measuring low-energy ions and neutral atoms ( keV particles replacing conventional detectors for certain applications in this paper. Our results demonstrated that the VUV-SiPM was sensitive above 1 keV both for electron pulses and protons. Using absolute beam monitor system, the proton detection efficiency of these SiPMs was evaluated. The efficiency was ~1% for 1-keV protons and plateaued above 5–6 keV at the expected 75% efficiency that agreed reasonably with the Monte Carlo numerical simulation results. The 75% plateau level was matching the open area ratio of the SiPM structure. The electron-pulse efficiency was also estimated by applying the same model, which shows ~1-keV detection limit and plateau above 3–4 keV. The agreement between the simulation and measurement shows that the dominating mechanism to trigger SiPM signals is the ionization loss of primary electrons and protons in the active volume of the pixel. An analytic investigation shows that the dark count rate can be significantly reduced with a double (or quadruple) coincidence measurement if multiple electrons can be produced from a single event.

Dementia associated with the Alzheimer's disease is thought to be correlated with the conversion of the β - Amyloid (Aβ) peptides from soluble monomers to aggregated oligomers and insoluble fibrils. We present a discrete-time mathematical model for the aggregation of Aβ monomers into oligomers using concepts from chemical kinetics and population dynamics. Conditions for the stability and instability of the equilibria of the model are established. A formula for the number of monomers that is required for producing oligomers is also given. This may provide compound designers a mechanism to inhibit the Aβ aggregation.

The Interstellar Boundary Explorer (IBEX) frequently images the Earth's magnetosphere in Energetic Neutral Atoms (ENAs). In May 2013, there was an extended period of northward interplanetary magnetic field (IMF) while IBEX was imaging the Earth's magnetotail. During this period, IBEX imaged the development of the cold plasma sheet between about 15 and 20 Earth radii (RE) down the tail from the Earth. The ENA fluxes changed in both amplitude and average energy during this development. In addition, the plasma sheet may have thickened. At the end of the interval, the IMF turned southward and ENA fluxes decreased. The thickening of the plasma sheet suggests that the plasma in this region increases in both density and volume as it develops during extended periods of northward IMF. The decrease in the ENA flux suggests thinning of the plasma sheet and loss of plasma associated with the IMF turning.

An acoustic camera comprising a linear microphone array is used to image the thunder signature of triggered lightning. Measurements were taken at the International Center for Lightning Research and Testing in Camp Blanding, FL, during the summer of 2014. The array was positioned in an end-fire orientation thus enabling the peak acoustic reception pattern to be steered vertically with a frequency-dependent spatial resolution. On 14 July 2014, a lightning event with nine return strokes was successfully triggered. We present the first acoustic images of individual return strokes at high frequencies (>1 kHz) and compare the acoustically inferred profile with optical images. We find (i) a strong correlation between the return stroke peak current and the radiated acoustic pressure and (ii) an acoustic signature from an M component current pulse with an unusual fast rise time. These results show that acoustic imaging enables clear identification and quantification of thunder sources as a function of lightning channel altitude.

This study reports the performance of single crystal chemical vapor deposit diamond detectors for measuring space plasma and energetic particles : ~7 keV energy resolution for protons with a 14 keV threshold level, and good response linearity for ions and electrons as expected from Monte-Carlo calculations of primary particle energy loss. We investigated that these diamond detectors are able to operate at high temperature ( > 70 ° C ) and have fast response times ( 1 ns rise time). While silicon detectors have proven capability over this energy range for space plasma measurements, diamond detectors offer a faster response, higher temperature operation, greater radiation tolerance, and immunity to light.

Using energetic neutral atom (ENA) emission observations of the subsolar magnetopause measured by the Interstellar Boundary Explorer (IBEX), we study the correlation between the upstream interplanetary magnetic field (IMF) conditions and the spectral index of the source ion population. Our ENA data set includes hour-averaged ENA measurements at energies between ∼0.5 and ∼6 keV obtained by the IBEX High Energy ENA imager from January 2009 to May 2011. Under the condition of quiet geomagnetic activity (SYM-H index >−20 nT), we find that the shallower spectra in the suprathermal tail of the ion population of the subsolar magnetopause is weakly correlated (correlation coefficient of −0.30) with the shock angle of the Earth's bow shock, but not correlated with parameters related to magnetic reconnection (i.e., elevation and clock angle of the interplanetary magnetic field orientation). The observed correlation suggests suprathermal ion energization from diffusive shock acceleration and thus that the suprathermal ions in the subsolar magnetopause are of shocked solar wind origin. We also argue that the roles of magnetospheric ion leakage or ion acceleration by magnetic reconnection are reduced in the magnetopause emissions compared to shock acceleration processes.

Thin carbon foils are used in different environments for various purposes. For example, they are used in vacuum technology to create a barrier between two volumes, in space plasma instrumentation to detect the crossing of a particle passing through them, or as a stripper of electrons for high energy particles. In the case of a change of pressure on either side of the foil, the pressure differential creates mechanical stresses to the foil that can lead to irreversible damage. Few experiments have characterized the survivability of carbon foils as a function of pressure. In this study, we show measurements of the resistance to pressure of carbon foils (CF) up to partial rupture. The focus is on ultra-thin carbon foils (e.g., 0.5–1.0 μg/cm2) that are typically used in space plasma instrumentation. However, our results can be used in other areas of experimental physics. Our results show that the finer the pitch of the supporting grid, the more pressure resistant the foil is, indicating that the CF support grid is perhaps more important in the design trade than the foil thickness. For example, we find that nominal 1.0 μg/cm2 foils mounted on 13.1 lpmm (333 lines per inch) nickel grids can hold a remarkable static pressure of ∼9 kPa (∼1.3 psi) with almost no damage.

[1] 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.

[1] We report on the time evolution of energetic neutral atom (ENA) emissions measured by the Interstellar Boundary Explorer (IBEX) during instances of compressed and expanded dayside magnetosheath. The ENA observations, taken during the passage of a corotating interaction region on 27 and 28 November 2010, are compared with in situ observations from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft. IBEX's field of view (6.5° full width at half maximum) covered a wide region of the dayside magnetosheath for several days, providing continuous information from that region. The high sensitivity and high-energy resolution of IBEX instruments enabled unprecedented remote-sensing diagnostics of dayside magnetosheath ENA spectra at energies between ~0.1 and ~6 keV, which can be directly compared with various upstream parameters. The inferred plasma spectra from ENA observations showed characteristic suprathermal tails described by kappa distributions that correlate well with the solar wind cone angle and are in agreement with in situ observations, suggesting that the shock angle contributed to magnetosheath particle heating. Simultaneous in situ ion measurements in the dayside magnetosheath provided by THEMIS agree reasonably well with IBEX-inferred spectra, demonstrating synergy between remote IBEX ENA observations (global) and in situ measurements (local) for studying localized magnetospheric processes.

The solar wind continuously flows out from the Sun filling interplanetary space and directly interacting with the surfaces of small planetary bodies and other objects throughout the solar system. A significant fraction of these ions backscatter from the surface as energetic neutral atoms (ENAs). The first observations of these ENA emissions from the Moon were recently reported from the Interstellar Boundary Explorer (IBEX). These observations yielded a lunar ENA albedo of similar to 10 and showed that the Moon reflects similar to 150 metric tons of neutral hydrogen per year. More recently a survey of the first 2.5 years of IBEX observations of lunar ENAs was conducted for times when the Moon was in the solar wind. Here we present the first IBEX ENA observations when the Moon is inside the terrestrial magnetosheath and compare them with observations when the Moon is in the solar wind. Our analysis shows that: (1) the ENA intensities are on average higher when the Moon is in the magnetosheath (2) the energy spectra are similar above similar to 0.6 solar wind energy but below there are large differences of the order of a factor of 10 (3) the energy spectra resemble a power law with a "hump" at similar to 0.6 solar wind energy and (4) this "hump" is broader when the Moon is in the magnetosheath. We explore potential scenarios to explain the differences namely the effects of the topography of the lunar surface and the consequences of a very different Mach number in the solar wind versus in the magnetosheath. (C) 2013 Elsevier Ltd. All rights reserved.

We demonstrate the performance of a large-area avalanche photodiode array as a medium-energy electron detector. This avalanche photodiode array is composed of eight pixels with 1.2 cm2 of total active area. The energy resolution (DeltaE/E) is as low as 4.5% in full width at half maximum for 25-keV electrons, and the linearity is excellent. Monte Carlo modeling by Geant4 shows that the detection efficiency of this device is appropriate for the detection of electrons ranging from 200 keV. This new device can be coupled with magnetic deflectors, electrostatic analyzers, and other physics instruments requiring position-sensitive or large-area solutions for the detection of electrons in this energy range.

Using a NaI(Tl) scintillation detector designed to operate in electrically noisy environments, we observed intense bursts of energetic radiation (≫10 kiloelectron volts) during the dart leader phase of rocket-triggered lightning, just before and possibly at the very start of 31 out of the 37 return strokes measured. The bursts had typical durations of less than 100 microseconds and deposited many tens of megaelectron volts into the detector. These results provide strong evidence that the production of runaway electrons is an important process during lightning.

This study provides, for the first time, complete and validated observations from the first three years (2009-2011) of the Interstellar Boundary Explorer (IBEX) mission. Energetic neutral atom (ENA) fluxes are corrected for both the time-variable cosmic ray background and for orbit-by-orbit variations in their probability of surviving en route from the outer heliosphere in to 1 AU where IBEX observes them. In addition to showing all six six-month maps, we introduce new annual ram and anti-ram maps, which can be produced without the need for algorithm-dependent Compton-Getting corrections. Together, the ENA maps, data, and supporting documentation presented here support the full release of these data to the broader scientific community and provide the citable reference for them. In addition, we show that heliospheric ENA emissions have been decreasing over the epoch from 2009 to 2011 with the IBEX Ribbon decreasing by the largest fraction and only the heliotail (which is offset from the down wind direction by the interstellar magnetic field) showing essentially no reduction and actually some increase. Finally, we show how the much more complete observations provided here strongly indicate a quite direct and latitude-dependent solar wind source of the Ribbon.