eV Protons Research Articles

Enhanced Solar Wind Dynamic Pressure as a Driver of Low‐Energy Proton Temperature Anisotropies and High‐Frequency EMIC Waves

AbstractTypical and high‐frequency electromagnetic ion cyclotron (EMIC) waves were simultaneously registered by satellites in the afternoon sector of the inner magnetosphere during enhanced solar wind dynamic pressure (Pdyn) on 3 November 2015. The compression of the dayside magnetosphere leads to amplified field intensities and squeezed field lines, which causes adiabatic accelerations of both hot (10s keV) and low‐energy (10s–100s eV) protons at the equatorial region. Temperature anisotropies of low‐energy protons enhance in immediate response to Pdyn impact accompanied by the generation of EMIC waves with frequencies close to proton gyrofrequencies. The low‐energy protons with enhanced fluxes are found to resonate with the high‐frequency EMIC waves, indicating their potential contributions to wave excitation. The comprehensive analysis of this work provides a new physical scenario describing the evolution of low‐energy protons and the generation of high‐frequency EMIC waves, reflecting the critical role of Pdyn in magnetospheric plasma dynamics.

Energization of Cold Protons and Helium Ions by EMIC Waves in the Inner Magnetosphere: Hybrid Simulations

AbstractElectromagnetic ion cyclotron (EMIC) waves generated by hot anisotropic (T⊥ > T∥) protons (∼10–100 keV), play an important role in accelerating cold (<1 eV) protons (H+) and helium (He+) ions in the magnetosphere. Using a hybrid code with parameters found in the inner magnetosphere, we examine when and how cold H+ and He+ ions are energized by EMIC waves. Hybrid simulations show that the energization of the cold particles occurs in two steps. In the first step, EMIC waves, which are linearly excited in the early stage of the simulation, interact with cold H+ and He+ ions, resulting in energization mostly in the direction perpendicular to the background magnetic field. The energization in this step is mainly contributed by enhanced bulk motion of these ions as a result of the linear response, consistent with recent observations in the inner magnetosphere. In the second step, nonlinear evolution of energized cold H+ and He+ ions are confirmed in the parallel direction, which is seen after about 200 proton gyroperiods (∼8.5 s). Throughout the simulation run, cold He+ ions are much more energized in the perpendicular direction than in the parallel direction. However, the cold protons are more energized in the parallel direction than in the perpendicular direction after 500 proton gyroperiods (∼21.3 s). By comparing recent observations and the present simulation results, we suggest that the cold particle energization by EMIC waves occurs at an early stage of wave generation when the nonlinear evolution of EMIC waves is not dominant in the inner magnetosphere.

Dependence of Quasi‐Electrostatic Magnetosonic Wave Generation on Plasma Density and Suprathermal Protons

AbstractMagnetosonic (MS) wave is one of the most common electromagnetic emissions in the magnetosphere, while quasi‐electrostatic magnetosonic (QEMS) waves are seldom observed. Here we present an interesting QEMS event detected by Van Allen Probe A on 9 January 2014, in which the presence of multi‐band QEMS emissions shows evident correlations with relatively low plasma densities (∼10 cm−3) and enhancements of suprathermal (∼10 − 100 eV) proton fluxes. Based on the observed proton distributions, simulations demonstrate very similar profiles to the observed QEMS in the wave spectral characteristics. Parametric studies indicate that the QEMS growth rate can increase by ∼20 times with the plasma density decreasing from 50 to 10 cm−3. Effective growth rates of higher‐band QEMS occur when the suprathermal proton population is sufficiently large. This study reveals that low densities and large suprathermal proton populations are favorable for generating distinct multi‐band QEMS in the magnetosphere.

Unusual high frequency EMIC waves: Detailed analysis of EMIC wave excitation and energy coupling between EMIC and magnetosonic waves

• Testing high frequency EMIC waves generation by anisotropic suprathermal protons. • Cyclotron resonance with magnetosonic waves is inefficient in thermal proton heating. • Quantitative understanding of the magnetosonic-EMIC energy coupling process is needed. A recent event study suggested a coupling process whereby suprathermal protons (10–100 eV), as a result of perpendicular heating by pre-existing magnetosonic waves, can excite electromagnetic ion cyclotron (EMIC) waves with frequency near the local proton cyclotron frequency ( f ~ 0.95 f cp ). The present study tests this coupling process. First, one-dimensional hybrid (kinetic ions/massless fluid electrons) simulations of parallel-propagating EMIC waves initialized with the plasma conditions derived from the event prove that high frequency EMIC waves can be generated by anisotropic suprathermal protons instead of more energetic (10s of keV) ring current protons. Calculation of the quasilinear pitch-angle diffusion coefficient for electrons using the simulated waves suggests that these high frequency EMIC waves outside the plasmasphere can play a role in the pitch-angle scattering of ~ MeV electrons due to the large wavenumber of the excited EMIC waves. Second, the role of the pre-existing magnetosonic waves in the suprathermal proton heating is examined using quasilinear diffusion theory and simple test particle calculation. It is found that the quasilinear diffusion becomes ineffective in energies relevant to the suprathermal protons, indicating that the low-energy ( < 10 eV) protons cannot be efficiently energized to the observed level through multi-harmonic cyclotron resonances with the magnetosonic waves observed. Rather, some kind of non-resonant process may have been at play, if the magnetosonic waves were actually involved in the heating. This result suggests that more quantitative understanding of the suggested energy coupling process through magnetosonic waves is needed.

Low energy proton irradiation tolerance of molybdenum disulfide lubricants

As the world’s space agencies look to long duration spaceflight beyond low earth orbit, engineering materials in deep space flight will endure galactic cosmic ray irradiation, of which 85% is protons. Characterization of proton irradiation damage near the threshold displacement energy is required to understand the mechanisms behind performance degradation and the fluence dependent effects of a thermalized spectrum on surface sensitive tribological characteristics. Here, tribological degradation of a space-grade molybdenum disulfide lubricant exposed to low energy (500 eV) protons is investigated as a function of fluence. A 21% increased coefficient of friction and 86% increase in wear rate is measured at 1020H/m2, and 170% increased CoF and 465% increased wear rate at 3·1023H/m2. Associated softening and decreased stiffness is measured by nanoindentation. X-ray photoelectron spectroscopy and Raman spectroscopy identify the mechanism of tribological degradation as being the preferential removal of sulfur leading to a disordered and reactive non-stoichiometric MoS2-x surface with compromised tribological properties. Missions beyond low-earth orbit will be required to withstand GCR radiation, and it is not suggested that the density of radiation damage sustained will be acutely detrimental to MoS2 lubricants. Still, research missions should plan to characterize the magnitude of radiation damage effects.

Theoretical investigations of collision dynamics of cytosine by low-energy (150–1000 eV) proton impact**Project supported by the National Natural Science Foundation of China (Grant Nos. 11905160 and 11635003) and the Natural Science Foundation of Jiangsu Province of China (Grant No. BK20160199).

Using a real-space real-time implementation of time-dependent density functional theory coupled to molecular dynamics (TDDFT-MD) nonadiabatically, we theoretically study both static properties and collision process of cytosine by 150–1000 eV proton impact in the microscopic way. The calculated ground state of cytosine accords well with experiments. It is found that proton is scattered in any case in the present study. The bond break of cytosine occurs when the energy loss of proton is larger than 22 eV and the main dissociation pathway of cytosine is the breaks of C1N2 and N8H10. In the range of 150 eV ≤ Ek ≤ 360 eV, when the incident energy of proton increases, the excitation becomes more violent even though the interaction time is shortened. While in the range of 360 eV < Ek ≤ 1000 eV, the excitation becomes less violent as the incident energy of proton increases, indicating that the interaction time dominates mainly. We also show two typical collision reaction channels by analyzing the molecular ionization, the electronic density evolution, the energy loss of proton, the vibration frequency and the scattering pattern detailedly. The result shows that the loss of electrons can decrease the bond lengths of C3N8 and C5N6 while increase the bond lengths of C4H11, C5H12 and C4C5 after the collision. Furthermore, it is found that the peak of the scattering angle shows a little redshift when compared to that of the loss of kinetic energy of proton.

Muon content of extensive air showers: Comparison of the energy spectra obtained by the Sydney University Giant Air-shower Recorder and by the Pierre Auger Observatory

The Sydney University Giant Air-shower Recorder (SUGAR) measured the energy spectrum of ultra-high-energy cosmic rays reconstructed from muon-detector readings, while the Pierre Auger Observatory, looking at the same Southern sky, uses the calorimetric fluorescence method for the same purpose. Comparison of their two spectra allows us to reconstruct the empirical dependence of the number of muons in the shower on the primary energy for energies between $10^{17}$ and $10^{18.5}$ eV. We compare this dependence with the predictions of hadronic interaction models \mbox{QGSJET-II-04} and \mbox{EPOS-LHC}. The empirically determined number of muons with energies above 0.75 GeV exceeds the simulated one by the factors $\sim$1.67 and $\sim$1.28 for $10^{17}$ eV proton and iron primaries, respectively. The muon excess grows moderately with the primary energy, increasing by an additional factor of $\sim 1.2$ for $10^{18.5}$ eV primaries.

Proton and hydrogen transport through two-dimensional monolayers

Diffusion of protons and hydrogen atoms in representative two-dimensional materials is investigated. Specifically, density functional calculations were performed on graphene, hexagonal boron nitride (h-BN), phosphorene, silicene, and molybdenum disulfide (MoS2) monolayers to study the surface interaction and penetration barriers for protons and hydrogen atoms employing finite cluster models. The calculated barrier heights correlate approximately with the size of the opening formed by the three-fold open sites in the monolayers considered. They range from 1.56 eV (proton) and 4.61 eV (H) for graphene to 0.12 eV (proton) and 0.20 eV (H) for silicene. The results indicate that only graphene and h-BN monolayers have the potential for membranes with high selective permeability. The MoS2 monolayer behaves differently: protons and H atoms become trapped between the outer S layers in the Mo plane in a well with a depth of 1.56 eV (proton) and 1.5 eV (H atom), possibly explaining why no proton transport was detected, suggesting MoS2 as a hydrogen storage material instead. For graphene and h-BN, off-center proton penetration reduces the barrier to 1.38 eV for graphene and 0.11 eV for h-BN. Furthermore, Pt acting as a substrate was found to have a negligible effect on the barrier height. In defective graphene, the smallest barrier for proton diffusion (1.05 eV) is found for an oxygen-terminated defect. Therefore, it seems more likely that thermal protons can penetrate a monolayer of h-BN but not graphene and defects are necessary to facilitate the proton transport in graphene.

Impact of cold O+ ions on the generation and evolution of EMIC waves

We explore the effect of cool O+ ions (~11 eV) on the generation and nonlinear evolution of electromagnetic ion cyclotron (EMIC) waves in the magnetosphere, using hybrid (kinetic ions, fluid electrons) simulations with a dipolar magnetic field. The instability is driven by the temperature anisotropy of the hot (keV), ring current protons whose density is a few percent of the background plasma consisting of cold (eV) protons and O+ ions with concentrations varying between 0 and 30% of the cold protons. The results show that for O+ ion concentration of 7% or less, the properties of the EMIC waves are similar to those in the absence of O+ ions where waves are generated at low latitudes and propagate all the way to the ionospheric boundary. Further increases in O+ density (~15%) result in waves being confined in latitude due to processes explored in this paper. At O+ densities of 30% and higher, the growth of EMIC waves is weak or non‐existent due to cyclotron resonant damping by the O+ ions. Comparing the results of the runs with no and 15% O+ ions shows that the propagation properties of the EMIC waves change dramatically in the presence of O+ ions. Specifically, they show that waves are propagating parallel and anti‐parallel to the magnetic field in both hemispheres due to reflection at points that move to higher latitudes with time. This in turn results in the nonlinear generation of field aligned electrostatic waves with large perturbations in the density of the cold protons and O+ ions and also local heating of these ions. Examination of the wave properties also shows that EMIC waves are only present in regions of space where the density of the hot protons is larger than 1% of the background level. In other words, the propagation properties of the EMIC waves are controlled by the density of the hot protons. This finding is further confirmed by performing a test hybrid simulation in which hot protons reaching latitude of 22° are removed from the run resulting in the confinement of the waves to this and lower latitudes.

ANOMALOUS TRANSPORT OF HIGH-ENERGY COSMIC RAYS IN GALACTIC SUPERBUBBLES. I. NUMERICAL SIMULATIONS

We present a simple continuous-time random-walk model for the transport of energetic particles accelerated by a collection of supernova explosions in a galactic superbubble, developed to simulate and highlight signatures of anomalous transport on the particles' evolution and their spectra in a multi-shock context. We assume standard diffusive shock acceleration (DSA) theory for each shock encounter. The superbubble (an OB stars association) is idealized as a heterogeneous region of particle sources and sinks bounded by a random surface. The model is based on two coupled stochastic differential equations and is applied for protons and alpha particles. Using characteristic values for a typical bubble, our simulations suggest that acceleration and transport in the bubble may be sub-diffusive. In addition, a spectral break in the particles' evolution and spectra is evident located at ≈1015 eV for protons and ≈3 × 1015 eV for alphas. Our simulations are consistent with a bubble's mean magnetic field strength of ≈1 μG and a shock separation distance ~0.1 × the characteristic radius of the bubble. The simulations imply that the diffusion coefficient (for the elementary shock acceleration process) is 1027 cm2 s–1 at 1 GeV/c. While the sub-diffusive transport is readily attributed to the stochastic nature of the acceleration time according to DSA theory, the spectral break appears to be an artifact of transport in a finite medium. These simulations point to a new and intriguing phenomenon associated with the statistical nature of collective acceleration of high-energy cosmic rays in galactic superbubbles.

LOWER LIMITS ON ULTRAHIGH-ENERGY COSMIC RAY AND JET POWERS OF TeV BLAZARS

Lower limits on the power emitted in ultrahigh-energy cosmic rays (UHECRs), which are assumed to be protons with energy 1e17-1e20 eV, are derived for TeV blazars with the assumption that the observed TeV gamma rays are generated due to interactions of these protons with cosmic microwave photons. The limits depend on the spectrum of the injected UHECR protons. While for a -2.2 injection spectrum, the lower limits on the powers emitted in UHECRs by 1ES 0229+200, 1ES 1101-232 and 1ES 0347-121 are lower than their respective synchrotron luminosities (1e46 erg/s); in the case of 1ES 1426+428 it exceeds the corresponding synchrotron luminosity by up to an order of magnitude. The proposed Auger North Observatory should be able to detect 4e19 eV cosmic ray protons from 1ES 1426+428 within a few years of operation and test the TeV gamma-ray production model by UHECR energy losses while propagating along the line-of-sight, or constrain the intergalactic magnetic field to be larger than 1e-16 G in case of no detection. The lower limits on the apparent-isotropic jet power from accelerated 1e10-1e20 eV proton spectra in the blazar jet is of the order of the Eddington luminosity of a 1e9 solar mass black hole for a cosmic-ray injection spectrum -2.2 or harder for all blazars considered except for 1ES 1426+428. In the case of the latter the apparent-isotropic jet power exceeds the Eddington luminosity by an order of magnitude. For an injection spectrum softer than -2.2, as is required to fit the observed cosmic-ray data above 1e17-1e18 eV, the Eddington luminosity is exceeded by the lower limits on the jet power for all blazars considered.

Identifying Nearby Accelerators of Ultrahigh Energy Cosmic Rays Using Ultrahigh Energy (and Very High Energy) Photons

Ultrahigh energy photons (UHE, E>10(19) eV) are inevitably produced during the propagation of approximately 10(20) eV protons in extragalactic space. Their short interaction lengths (<20 Mpc) at these energies, combined with the impressive sensitivity of the Pierre Auger Observatory detector to these particles, makes them an ideal probe of nearby ultrahigh energy cosmic ray (UHECR) sources. We here discuss the particular case of photons from a single nearby (within 30 Mpc) source in light of the possibility that such an object might be responsible for several of the UHECR events published by the Auger collaboration. We demonstrate that the photon signal accompanying a cluster of a few >6 x 10(19) eV UHECRs from such a source should be detectable by Auger in the near future. The detection of these photons would also be a signature of a light composition of the UHECRs from the nearby source.

Auroral ion outflow: low altitude energization

Abstract. The SIERRA nightside auroral sounding rocket made observations of the origins of ion upflow, at topside F-region altitudes (below 700 km), comparatively large topside plasma densities (above 20 000/cc), and low energies (10 eV). Upflowing ions with bulk velocities up to 2 km/s are seen in conjunction with the poleward edge of a nightside substorm arc. The upflow is limited within the poleward edge to a region (a) of northward convection, (b) where Alfvénic and Pedersen conductivities are well-matched, leading to good ionospheric transmission of Alfvénic power, and (c) of soft electron precipitation (below 100 eV). Models of the effect of the soft precipitation show strong increases in electron temperature, increasing the scale height and initiating ion upflow. Throughout the entire poleward edge, precipitation of moderate-energy (100s of eV) protons and oxygen is also observed. This ion precipitation is interpreted as reflection from a higher-altitude, time-varying field-aligned potential of upgoing transversely heated ion conics seeded by the low altitude upflow.

Reanalysis of plasma measurements at geosynchronous orbit

Retrospective analyses of spacecraft anomalies, especially surface charging, require information about the local plasma environment. Such information is usually not available at geosynchronous orbit because most vehicles lack appropriate sensors. We have constructed a nearly continuous hourly database covering four plasma moments at geosynchronous orbit: density and temperature for hot (energies &gt; 100 eV) protons and electrons. The four moments are provided for 24 hourly fiducial local time bins and cover the years 1990–2005. We apply an ensemble of simple models to “fill in” the local time gaps between plasma measurements at geosynchronous orbit made by Los Alamos sensors. Validation on artificial data gaps shows that the reconstruction has rank order correlations ranging from 0.65 to 0.97, depending on bulk moment and local time. As a demonstration, we include a comparison of our reanalysis electron temperature to on‐orbit surface charging measurements at a vehicle that lacks a plasma sensor. In addition to anomaly analyses, the reanalysis database we have produced can be used to provide geosynchronous boundary conditions for numerical simulations of the inner magnetosphere and temporal variations at a single location for statistical studies.

Photodissociation of organic molecules in star-forming regions

The presence of methyl alcohol or methanol (CH 3 OH) in several astrophysical environments has been characterized by its high abundance that depends on both the production late and the destruction rate. In the present work, the photoionization and photodissociation processes of methanol have been experimentally studied, employing soft X-ray photons (100-310 eV) from a toroidal grating monochromator (TGM) beamline of the Brazilian Synchrotron Light Laboratory (LNLS). Mass spectra were obtained using the photoelectron photoion coincidence (PEPICO) method. Kinetic energy distribution and abundances for each ionic fragment have been obtained from the analysis of the corresponding peak shapes in the mass spectra. Absolute photoionization and photodissociation cross sections were also determined. We have found, among the channels leading to ionization, about 11-16% of CH 3 OH survive the soft X-rays photons. This behavior, together with an efficient formation pathways, may be associated with the high column density observed in star-forming regions. The three main photodissociation pathways are represented by COH + (or HCO + ) ion release (with ejection of H 2 + H), the dissociation via C-O bond rupture (with strong charge retention preferentially on the methyl fragment) and the ejection of a single energetic (2-4 eV) proton. Since methanol is very abundant in star forming regions, the produced protons could be an alternative route to molecular hydrogenation or a trigger for secondary dissociation processes or even to promote extra heating of the environment.

Ionic yield and dissociation pathways from soft X-ray multi-ionization of acetic acid

We present data from inner shell excitation and multi-ionization of acetic acid with synchrotron radiation at at energies around C 1s edge. The measurements were taken at the Brazilian Synchrotron Light Laboratory (LNLS) and at center for advanced microstructures & devices (CAMD), employing soft X-ray photons (200–310 eV) from a toroidal grating monochromator (TGM) beamline. The main dissociation route were the secondary decay after deferred charge separation (SDDCS) process and deferred charge separation (DCS) processes. The main dissociation channels were associated to the ions pairs H + + C + , H + + CH + , H + + CH 2 + , H + + O + , H + + CO + and H + + COH + . About 70–80% of the dissociation channels leads to the production of energetic (3–7 eV) protons. The ejection of reactant radical COOH + was seen in about 7–10% of the channels.

The Galactic magnetic field as spectrograph for ultra-high energy cosmic rays

We study the influence of the regular component of the Galactic magnetic field (GMF) on the arrival directions of ultra-high energy cosmic rays (UHECRs). We find that, if the angular resolution of current experiments has to be fully exploited, deflections in the GMF cannot be neglected even for E = 10 20 eV protons, especially for trajectories along the Galactic plane or crossing the Galactic center region. On the other hand, the GMF could be used as a spectrograph to discriminate among different source models and/or primaries of UHECRs, if its structure would be known with sufficient precision. We compare several GMF models introduced in the literature and discuss for the example of the AGASA data set how the significance of small-scale clustering or correlations with given astrophysical sources are affected by the GMF. We point out that the non-uniform exposure to the extragalactic sky induced by the GMF should be taken into account estimating the significance of potential (auto-) correlation signals.

Pc 1 waves and associated unstable distributions of magnetospheric protons observed during a solar wind pressure pulse

We present observations of Pc 1 waves (∼0.6 Hz) that occurred shortly after a strong (&gt;20 nPa) compression of Earth's magnetosphere at 1321 UT, 18 March 2002. Intense Pc 1 waves were observed at several high‐latitude ground stations in Antarctica and Greenland from 1321 UT to beyond 1445 UT. Two wave bursts were recorded at the Polar satellite at 1338 and 1343–1344 UT as it passed outbound in the Southern Hemisphere at 1154 local time (SM magnetic latitude of −22° and near L = 7.5) in good magnetic conjunction with the Antarctic. The pressure increase created a significant population of protons between a few hundred eV and several keV, whose fluxes were mostly perpendicular to B. These protons seem to have replaced the quiescent stream of protons (presumably convected from the plasma sheet) that existed before this increase. There was also a nearly two‐order‐of‐magnitude increase in the population of thermal/suprathermal (0.32–410 eV) protons. The generation of ion cyclotron waves is expected to limit the proton temperature anisotropy A, defined as T⊥/T∥ − 1. The ion cyclotron instability driven by the observed hot ion temperature anisotropy is studied using two models, with and without the presence of cold background plasma. Peaks in the calculated instability as a function of time show excellent agreement with the times of the Polar wave bursts, which were measured a few tens of seconds after maxima in the instability calculation. The time delay is consistent with the propagation time to the spacecraft from a source nearer to the equatorial plane. The hot proton population at Polar appears to be driven back to stability by a sudden increase in very field‐aligned protons having energies less than the hot perpendicular population, suggesting a different source for the two populations. These observations confirm the importance of both the energization and/or increase in population of protons transverse to B in the several keV range (possibly betatron acceleration as a result of the pressure pulse), and the presence of greatly increased fluxes of lower energy protons (100s of eV to a few keV), predominantly aligned along B, in determining whether the particle population is unstable at a given time.

Diffusion of ultra-high energy protons in galaxy clusters and secondary X- and gamma-ray emissions

In this work we simulate the propagation of ultra-high energy (UHE) protons in the magnetised intergalactic medium of galaxy clusters (GCs). Differently from previous works on the subject, we trace proton trajectories in configurations of the intra-cluster magnetic field (ICMF), which have been extracted from a constrained magnetic-SPH simulation of the local universe. Such an approach allows us to take into account the effects of several features of the ICMFs, e.g. irregular geometrical structure and field fluctuations due to merger shocks, which cannot be investigated analytically or with usual numerical simulations. Furthermore, we are able to simulate a set of clusters, which have properties quite similar to those of GCs observed in the nearby universe. We estimate the time that UHE protons take to get out of the clusters and found that in the energy range 5×1018≲E≲3×1019 eV proton propagation takes place in the Bohm scattering diffusion regime passing smoothly to a small pitch angle diffusion regime at larger energies. We apply our results to estimate the secondary gamma- and hard X-ray (HXR) emissions produced by UHE protons in a rich GC. We show that the main emission channel is due to the synchrotron HXR radiation of secondary electrons originated by proton photo-pair production scattering onto the CMB. This process may give rise to a detectable signal if a relatively powerful AGN, or a dead quasar, accelerating protons at UHEs is harboured by a rich GC in the local universe.

A zero-to-few-hundred eV proton beam for calibrations of neutron β decay experiments

We have constructed a system using a duoplasmatron source to produce a beam of low-energy (0 – few hundred eV) protons with the principal goal of testing and calibrating detectors used to detect protons from neutron β decay. The system is stable and produces beams by simply turning on the associated power supplies without the need of careful tuning. As an example we show data from calibration of a surface barrier detector in the emiT apparatus. Protons from the system were scattered from an Al target and used to calibrate detectors in the emiT apparatus.