The High-Energy Ion Telescope (HIT) for the Interstellar Mapping And Acceleration Probe (IMAP) Mission

The leading hypothesis for the origin of the Interstellar Boundary Explorer (IBEX) "ribbon" of enhanced energetic neutral atoms (ENAs) from the outer heliosphere is the secondary ENA mechanism, whereby neutralized solar wind ions escape the heliosphere and, after several charge-exchange processes, may propagate back toward Earth primarily in directions perpendicular to the local interstellar magnetic field (ISMF). However, the physical processes governing the parent protons outside of the heliopause are still unconstrained. In this study, we compute the "spatial retention" model proposed by Schwadron & McComas (2013) in a 3D simulated heliosphere. In their model, pickup ions outside the heliopause that originate from the neutral solar wind are spatially-retained in a region of space via strong pitch angle scattering before becoming ENAs. We find that the ribbon's intensity and shape can vary greatly depending on the pitch angle scattering rate both inside and outside the spatial retention region, potentially contributing to the globally distributed flux. The draping of the ISMF around the heliopause creates an asymmetry in the average distance to the ribbon's source as well as an asymmetry in the ribbon's shape, i.e., radial cross section of ENA flux through the circular ribbon. The spatial retention model adds an additional asymmetry to the ribbon's shape due to the enhancement of ions in the retention region close to the heliopause. Finally, we demonstrate how the ribbon's structure observed at 1 au is affected by different instrument capabilities, and how the Interstellar Mapping and Acceleration Probe (IMAP) may observe the ribbon.

The Frontier Solid State Power Amplifier (SSPA), developed at the Johns Hopkins University Applied Physics Laboratory (JHU/APL) to support NASA's Interstellar Mapping and Acceleration Probe (IMAP) mission, is scheduled to launch in 2025. In order to provide reliable communications within a cost, schedule, and mass constrained mission, an SSPA was selected. The SSPA can operate over the International Telecommunication Union (ITU) Near Earth and Deep Space downlink frequency band of 8400–8500 MHz and provides a minimum of 10 W of RF output power, with a nominal efficiency of 31.5%, and a mass of less than 1.1kg. The SSPA consists of two standalone boxes, an RF Amplifier Box and a Power Converter Unit (PCU), connected via an interbox harness. The RF Amplifier box design utilizes three single-string hybrid amplifiers, an isolator, DC bias circuitry, and thermistor-based gain control. The hybrid amplifiers were designed using commercially available GaN transistors that have successfully been screened for the harsh space environment. The transistor is impedance matched at the input and output using microstrip transmission lines and thin-film resistors on alumina substrates, and sealed in a hermetic package. The PCU is a buck-boost converter, which provides 30 V and -5 V secondary voltages from a primary voltage ranging from 22 V to 35 V, while maintaining proper turn on and turn off voltage sequencing. The Engineering Model (EM) SSPA assembly was subjected to a 3-axis sine and random vibration followed by thermal vacuum testing from -25°C to +55°C. The design methodology, analyses, such as thermal, structural, and multipactor, along with a comparison of pre and post environmental testing are presented.

Solar wind features a latitudinal structure that evolves during the solar activity cycle. The only in-situ measurements of the solar wind speed and density available so far were performed by Ulysses at the turn of the 20th and 21st centuries. They showed that when the solar activity is low, the wind is fast and rare, with an equatorial band filled with a slower but denser outflow. During epochs of high activity, the band of slow wind expands to all latitudes. However, details of possible north/south asymmetries and regular structure evolution at shorter time scales could not be established because the measurements were performed in-situ along a highly elliptical orbit with a period of the order of half of the solar cycle.Complementary methods of monitoring the solar wind latitudinal profiles include remote-sensing observations such as interplanetary scintillations (IPS) and hydrogen Lyman-α backscatter glow observations. Existing analyses of IPS and helioglow observations returned somewhat conflicting conclusions. Helioglow maps observed by SOHO/SWAN suggested that the solar wind flux temporarily features flux maxima at mid-latitudes. Analysis of IPS observations for equivalent times did not reveal such maxima in the solar wind speed.Insight from Ulysses resulted in a hypothesis that the energy flux of solar wind is latitudinally invariant, which cannot be verified without additional observations. A confirmation of this invariance would be an important milestone in the understanding of the solar wind emission mechanism and provide a handy tool supporting retrieval of the solar wind structure from observations of either IPS or the helioglow.GLObal solar Wind Structure (GLOWS) is a Lyman-α photometer onboard Interstellar Mapping and Acceleration Probe (IMAP), dedicated to helioglow observations aimed at retrieval of the solar wind structure. We present how GLOWS observations can be interpreted to resolve the helioglow/IPS solar wind structure dilemma and to verify the hypothesis of latitudinal invariance of the solar wind energy flux.

Evidence for two different physical mechanisms for acceleration of solar energetic particles (SEPs) arose 50 years ago with radio observations of type III bursts, produced by outward streaming electrons, and type II bursts from coronal and interplanetary shock waves. Since that time we have found that the former are related to "impulsive" SEP events from impulsive flares or jets. Here, resonant stochastic acceleration, related to magnetic reconnection involving open field lines, produces not only electrons but 1000-fold enhancements of 3He/4He and of (Z>50)/O. Alternatively, in "gradual" SEP events, shock waves, driven out from the Sun by coronal mass ejections (CMEs), more democratically sample ion abundances that are even used to measure the coronal abundances of the elements. Sometimes residual impulsive suprathermal ions contribute to the seed population for shock acceleration, complicating the abundance picture, but this process has now been modeled theoretically. Initially, impulsive events define a point source on the Sun, selectively filling few magnetic flux tubes, while gradual events show broad acceleration that can fill half of the inner heliosphere, beginning when the shock reaches ~2 solar radii. Shock acceleration occurs as ions are scattered back and forth across the shock by resonant Alfven waves amplified by the accelerated protons themselves. These waves also can produce a streaming-limited maximum SEP intensity and plateau region upstream of the shock. Behind the shock lies the large expanse of the "reservoir", a spatially extensive trapped volume of uniform SEP intensities with invariant energy-spectral shapes where overall intensities decrease with time as the enclosing "magnetic bottle" expands adiabatically. These reservoirs now explain the slow intensity decrease that defines gradual events, once erroneously attributed solely to slow outward diffusion.

The Sun drives a supersonic wind which inflates a giant plasma bubble in our very local interstellar neighborhood, the heliosphere. Its boundaries and the turbulent magnetic field shield the solar system from much of the interstellar medium as well as the low-energy portion of galactic cosmic rays (GCRs) which are accelerated primarily by super-nova-driven shocks in our galaxy. The heliosphere is bathed in an extremely variable background of energetic ions and electrons which originate from a number of sources. Solar energetic particles (SEPs) are accelerated in the vicinity of the Sun, whereas shocks driven by solar disturbances are observed to accelerate energetic storm particles (ESPs). Moreover, a dilute population with a distinct composition forms the anomalous cosmic rays (ACRs) which are of a mixed interstellar-heliospheric origin. Particles are also accelerated at planetary bow shocks. In February 2020, the European Space Agency (ESA) launched Solar Orbiter, a science mission to answer the question how the Sun creates and controls the heliosphere. Its orbit brings it within 0.3 astronomical units (au) from the Sun and will also reach moderately high solar latitudes to allow to understand why solar activity changes with time. The spacecraft carries instruments which observe the Sun and its surrounding remotely, others that measure the local environment, and some can track solar disturbances as they travel away from the Sun. The Energetic Particle Detector (EPD) on Solar Orbiter measures suprathermal and energetic particles in the energy range from a few keV up to (near-) relativistic energies (tens of MeV for electrons and about $> 100$ MeV/nuc for ions). Together with the other sophisticated instruments on Solar Orbiter it is designed to unravel how solar eruptions produce energetic particle radiation that fills the heliosphere. Since launch, EPD has made several advances about GCRs, SEPs, ACRs, ESPs, and the particles around the Venusian magnetosphere.

Solar energetic particle (SEP) events have been observed by the Parker Solar Probe (PSP) spacecraft since its launch in 2018. These events include sources from solar flares and coronal mass ejections (CMEs). The IS⊙IS instrument suite on board PSP is measuring ions over energies from ∼ 20 keV nucleon−1 to 200 MeV nucleon−1 and electrons from ∼ 20 keV to 6 MeV. Previous studies sought to group CME characteristics based on their plasma conditions and arrived at general descriptions with large statistical errors, leaving open questions on how to properly group CMEs based solely on their plasma conditions. To help resolve these open questions, the plasma properties of CMEs have been examined in relation to SEPs. Here, we reexamine one plasma property, the solar wind proton temperature, and compare it to the proton SEP intensity in a region immediately downstream of a CME-driven shock for seven CMEs observed at radial distances within 1 au. We find a statistically strong correlation between proton SEP intensity and bulk proton temperature, indicating a clear relationship between SEPs and the conditions in the solar wind. Furthermore, we propose that an indirect coupling of SEP intensity to the level of turbulence and the amount of energy dissipation that results is mainly responsible for the observed correlation between SEP intensity and proton temperature. These results are key to understanding the interaction of SEPs with the bulk solar wind in CME-driven shocks and will improve our ability to model the interplay of shock evolution and particle acceleration.

Based on the multiple-vantage observations of STEREO, SOHO, wind and other spacecraft, the fast and wide coronal mass ejections (CME) during the 24th solar cycle from January 2010 to September 2014 are selected in this paper. Using the outputs of Richardson’s (2014) empirical model of solar energetic particle (SEP) intensity under different conditions, the effects of its associations such as CME, pre-CME, and type II radio bursts, on SEP intensity are analyzed, and the relationship between SEP event and these characteristics is also discussed. The main conclusions are as follows. 1) The presence or absence of pre-CME within 13 h before fast CME significantly improves the model prediction effect and has a significant influence on whether fast CME produces SEP event. Compared with the events without pre-CMEs, the events with pre-CMEs have a low proportion of false alarms (FR: 47.7% <i>vs.</i> 70%). However, the number of pre-CMEs does not improve the model output. 2) CMEs with type-II radio bursts have significantly lower FR to generate SEP events than fast CMEs without type-II radio bursts (42% <i>vs.</i> 68%). And selecting type-II radio bursts as a constraint will filter out some small/weak SEP events, the relationship between model predictions and observations especially for large SEP events (e.g. <i>I</i><sub>p</sub> ≥ 0.01 pfu/MeV) will stand out. Moreover, if the type-II radio enhancement is taken into account, FR can be further reduced to 29.4%, and the proportion of hits can be further increased (HR: 48.5%), and the model prediction is significantly improved. 3) The larger the start frequency of type II radio bursts, the smaller the end frequency is, and FR decreases slightly, but at the same time, a large number of SEP events are excluded by this condition, and the results show that the constraints on the start/end frequency of type-II radio bursts do not improve the model predictions distinctly. 4) If the sub-classification of type-II radio bursts is considered as the model constraint, the CMEs associated with multi-band type-II radio bursts have better model predictions than those with single-band events. For example, m-DH-km type-II radio bursts have lower FR (35.4%) and higher HR (48%), and the accuracy of empirical model is higher. In summary, we find that in addition to the velocity and angular width of CME, the associations of pre-CME, type II radio bursts and their enhancement, and multi-band sub-classification are the favorable conditions for CME to generate SEP events. The SEP intensities obtained by the empirical model have better consistency with the observations, and better predictions can be obtained. This investigation indicates that SEP events are more likely generated by fast and wide CMEs accompanied by pre-CMEs, multi-band type II radio bursts and their enhancements, which seem to serve as discriminative signal for SEP-rich and SEP-poor CMEs.

Transient energetic (E> 10 MeV) particle events from the Sun have been observed at the Earth for half a century using several detection techniques. We review these observations and the change in focus from solar flares to fast coronal mass ejections (CMEs) and shocks as the causal agents of solar energetic particle (SEP) events. We review the properties of SEP events that are important for space weather: 1) the number distributions of peak SEP intensities and of SEP fluences; 2) the relationship of SEP intensities to CME speeds; 3) when SEP events occur during the solar cycle; and 4) where SEP events occur relative to the CME-driven shocks. We conclude with a discussion of two cases of direct negative effects of SEPs on space experiments.

view Abstract Citations (46) References (45) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The effect of losses on acceleration of energetic particles by diffusive scattering through shock waves Voelk, H. J. ; Morfill, G. E. ; Forman, M. A. Abstract A discussion of the effect of local losses on the acceleration of energetic particles by shocks is presented, which considers the energy losses of individual particles and the damping processes for the scattering hydromagnetic waves by means of time asymptotic and steady-state calculations. For acceleration to be a local effect within the Galaxy, the local scattering mean free path must be small by comparison with the effective overall galactic mean free path deduced from the cosmic-ray escape time. Given the spatial extent of the layer for strong shocks propagating into neutral interstellar clouds, the possibility of localized diffusive acceleration is investigated. The estimated strength and extent of the scattering region is not large enough to confine acceleration within the layer, which will instead extend across the entire cloud. The integrated losses of the cloud will then determine the efficiency. Publication: The Astrophysical Journal Pub Date: October 1981 DOI: 10.1086/159272 Bibcode: 1981ApJ...249..161V Keywords: Energetic Particles; Energy Dissipation; Interstellar Matter; Molecular Clouds; Particle Acceleration; Shock Wave Propagation; Cosmic Rays; Gas Ionization; Gaseous Diffusion; Magnetohydrodynamic Waves; Shock Wave Interaction; Stellar Winds; Wave Scattering; Astrophysics full text sources ADS |

With the rise of satellites and mankind's growing dependence on technology, there is an increasing awareness of space weather phenomena related to high-energy particles. Shock waves driven by coronal mass ejections (CMEs) and corotating interaction regions (CIRs) occasionally act as potent particle accelerators, generating hazardous solar energetic particles (SEPs) that pose risks to satellite electronics and astronauts. Numerical simulation tools capable of modelling and predicting large SEP events are thus highly demanded. We introduce the new Icarus+PARADISE model as an advancement of the previous EUHFORIA+PARADISE model. Icarus, based on the MPI-AMRVAC framework, is a three-dimensional magnetohydrodynamic code that models solar wind configurations from 0.1 au onwards, encompassing transient structures like CMEs or CIRs. Differing from EUHFORIA's uniform-only grid, Icarus incorporates solution adaptive mesh refinement (AMR) and grid stretching. The particle transport code PARADISE propagates energetic particles as test particles through these solar wind configurations by solving the focused transport equation in a stochastic manner. We validate our new model by reproducing EUHFORIA+PARADISE results. This is done by modelling the acceleration and transport of energetic particles in a synthetic solar wind configuration containing an embedded CIR. Subsequently, we illustrate how the simulation results vary with grid resolution by employing different levels of AMR.. The resulting intensity profiles illustrate increased particle acceleration with higher levels of AMR in the shock region, better capturing the effects of the shock.

It is extremely important to understand and model the Martian radiation environment in preparation for future human missions to Mars, especially during extreme and elevated conditions such as an intense solar energetic particle (SEP) event. Such events may enhance the radiation level drastically and should be forecasted as soon as possible to prevent severe damage to humans and equipment. Besides, the omnipresent galactic cosmic rays (GCRs) also contribute significantly to the radiation in space and on the surface of Mars and may cause long-term damages to current and future missions. Based on GEANT4 Monte Carlo simulations with the Martian atmospheric and regolith environment setup, we have calculated and obtained some ready-to-go functions which can be used to quickly convert any given SEP or GCR proton/helium ion spectra to the radiation dose on the surface of Mars and also at different depth of the atmosphere. We implement these functions to the RADMAREE tool under the Europlanet project which can be easily accessed by the public.

The inner heliosphere, spanning from the solar corona to Earth's orbit, is a dynamic region where energetic particles are accelerated and transported. Understanding these processes is crucial for comprehending space weather phenomena and their impact on Earth. This paper discusses the key mechanisms involved in particle acceleration near the Sun, primarily driven by solar flares and coronal mass ejections (CMEs), and the subsequent transport of these particles in the solar wind. Furthermore, we address the influence of Solar Energetic Particles (SEPs) and Galactic Cosmic Rays (GCRs) on the global electric circuit (GEC). SEPs, produced by solar flares and CMEs, and GCRs, originating from outside the solar system, both contribute to the ionization of the Earth's atmosphere. This ionization significantly impacts the conductivity of the atmosphere, particularly in the polar regions. Change of ionization due to SEPs and GCRs can alter the potential difference between the ionosphere and the ground, influencing the flow of current within the global electric circuit. These changes can lead to observable effects, such as variations in atmospheric conductivity and potential gradients, and may even influence weather patterns.

During mid-May 2024, active region (AR) 13664 produced a series of M- and X-class flares along with several coronal mass ejections (CMEs) which resulted in exceptionally strong aurora at Earth. This study presents in-situ solar energetic particle (SEP) ion composition data from STEREO-A, ACE and Parker Solar Probe (PSP) as their connectivity to AR 13664 varied throughout the great solar storm period. The observational period was between 08 to 20 May, STEREO-A was 12° longitudinally separated from ACE at 0.96 AU and the SEP intensities rose gradually as a result of several CMEs from AR 13664. Notable events for the spacecraft near Earth included a magnetic field strength jump to 88 nT and the appearance of aurora on Earth on 10 May. Additionally, on 13 May an M6 flare was followed by another SEP event with rapid onset and an estimated particle path length of 0.97 +/- 0.16 AU. PSP, set at approximately 95° longitudinal separation from Earth, was at 0.74 AU during the observational period. PSP measured a qualitatively similar gradually rising SEP intensities beginning on 11 May and continuing until the magnetic field strength rapidly increased to 100+ nT on 16 May coincident with a jump in SEP intensity. Finally, on 20 May an X16 flare from AR 13664 produced an Fe-rich SEP event. Throughout the observational period, AR 13664 produced flares and CMEs causing SEP events with Fe/O ratios that varied from

Through new missions and unusual solar conditions, solar cycle 24 has afforded the opportunity for expanding our understanding of solar energetic particle (SEP) acceleration and transport. With complementary SEP observations from multiple spacecraft separated significantly in longitude, it has been possible to examine the longitudinal distribution of energetic particles in individual events, rather than relying on statistical event studies. Unprecedented 360° views of the Sun, in multiple wavelengths and coronagraphs, has made it possible to identify solar source regions regardless of where they are located and to more accurately determine the properties of related coronal mass ejections. The unusually quiet conditions during the onset of cycle 24 allowed smaller SEP events to be examined and their source regions to be unambiguously identified. This paper reviews some of the unexpected results from multi-spacecraft SEP observations made over this solar cycle and discusses their implications for particle acceleration near the Sun and transport through the inner heliosphere.

Aims.Lunar soil and rocks are not protected by a magnetic field or an atmosphere and are continuously irradiated by energetic particles that can produce cosmogenic radioisotopes directly inside rocks at different depths depending on the particle’s energy. This allows the mean fluxes of solar and galactic cosmic rays to be assessed on the very long timescales of millions of years.Methods.Here we show that lunar rocks can serve as a very good particle integral spectrometer in the energy range 20–80 MeV. We have developed a new method based on precise modeling, that is applied to measurements of26Al (half-life ≈0.7 megayears) in lunar samples from theApollomission, and present the first direct reconstruction (i.e., without any a priori assumptions) of the mean energy spectrum of solar and galactic energetic particles over a million of years.Results.We show that the reconstructed spectrum of solar energetic particles is totally consistent with that over the last decades, despite the very different levels of solar modulation of galactic cosmic rays (ϕ= 496 ± 40 MV over a million years versus (ϕ= 660 ± 20 MV for the modern epoch). We also estimated the occurrence probability of extreme solar events and argue that no events with theF(>30 MeV) fluence exceeding 5×1010and 1011cm−2are expected on timescales of a thousand and million years, respectively.Conclusions.We conclude that the mean flux of solar energetic particles hardly depends on the level of solar activity, in contrast to the solar modulation of galactic cosmic rays. This puts new observational constraints on solar physics and becomes important for assessing radiation hazards for the planned space missions.