ASIF Space Radiation Environment (ASRE) and ASIF related Activities

The current webpage is organized in the following sections:

Space Radiation Environment within the Context of ASIF Activities and Radiation Damage Assessment for Space Missions

Scientific and Technological Activities, Tool Developments for ASIF Space Radiation Environment (ASRE) activities and ASIF related websites

People involved in space radiation environment activities within ASIF

Space Radiation Environment within the Context of ASIF Activities and Radiation Damage Assessment for Space Missions

Together with geomagnetically trapped particles and galactic cosmic rays, solar protons (and other ions, electrons) can pose a hazard to both manned spaceflight and the sensitive components used in satellite subsystems and instrumentation. The physical mechanisms for radiation-induced damages have been investigated for many decades. They are related, for instance, to the type of particle and its energy, the device type, and its material composition (e.g., see this webpage).
The structure of the Earth's magnetosphere, resulting from its almost dipolar internal magnetic field and the influence of the solar wind  (e.g., see Boschini et al. (2021) with references therein, and the ASIF related geomagnetic website), allows the formation of radiation belts. These belts contain trapped particles (not discussed here) that gyrate around geomagnetic field lines. However, for the assessment of expected radiation hazards in space missions outside the Earth's magnetosphere, one primarily needs to consider damages caused by solar energetic charged particles and galactic cosmic rays. In fact, trapped particles in the Earth's magnetosphere are unlikely to contribute significantly, for instance, on the planet's dayside, the subsolar distance (i.e., the radial distance in the direction of the Sun to the nose of the magnetopause) does not exceed about 10 Earth radii, approximately 0.00043 AU.
In the heliosphere, particles of solar origin (e.g., solar energetic charged particles) and those from our galaxy (galactic cosmic rays, GCRs, i.e., protons, electrons and nuclei with relative abundances drastically dropping above Z=28) dynamically modify their populations (i.e., the space radiation environment) due to the Sun's activity. This latter cyclically passes through low and high periods of activity (e.g., see NOAA space weather prediction center) every about 11 years (these are termed solar or sunspot cycles). Some time after a solar maximum, sun magnetic configuration is reversed e.g., see Svalgaard and Kamide, Asymmetric solar polar field reversals (2013)), so that it becomes similar every two solar cycles (termed Hale cycles or sometimes referred to as solar magnetic cycles), i.e., about 22 years. The properties of the solar wind (SW), such as its intensity and embedded magnetic field, are directly linked to solar activity. Parker in Dynamics of the Interplanetary Gas and Magnetic Fields (1958) suggested that the solar magnetic field is frozen-in to flow of the SW non-relativistic plasma, thereby creating the interplanetary magnetic field  (IMF). This solar wind, a plasma primarily composed of protons constituting the largest amount of positively charged particles (e.g., see Ogilvie and Coplan, Solar wind composition (1995)), plays a pivotal role in modulating the intensities of galactic cosmic rays. It streams continuously from the Sun's corona to the boundaries of the heliosphere, exhibiting significant variability over time and space.

Solar charged energetic particle events are a significant part of the near-Earth radiation environment, comprising protons (often called SEP), electrons, and heavier ions (e.g., see Zheng and Evans, Solar Energetic Particles (SEPs) (2014)). These events originate from particle acceleration in solar flares or/and shocks linked to coronal mass ejections (CMEs). During solar minima, about one CME per week is typical, while during solar maxima, there are around two to three per day, providing an indication of the frequency dependence of solar charged particles emission on solar activity. SEP intensities can surpass those of galactic cosmic rays (GCRs) by several orders of magnitude, with energies ranging from keVs with a tail  reaching up to GeVs. Many of these typically low-energy charged particles can penetrate spacecraft walls, accumulating both ionizing (TID) and non-ionizing (NIEL or TNID) doses (e.g., SR-NIEL website) in satellite instruments. TID and TNID doses from GCRs are usually less significant. Extensive literature exists regarding the modeling of solar energetic particles. For example, there are studies like Whitman et al., Review of Solar Energetic Particle Prediction Models (2023), Papaioannou et al, Nowcasting of Solar Energetic Particle Events using near real-time Coronal Mass Ejection characteristics in the framework of the FORSPEF tool (2018), Jiggens et al., Updated Model of the Solar Energetic Proton Environment in Space (2018), among others. Predicting the exact occurrence, intensity, or duration of solar proton events is hardly feasible. Many current solar energetic particle prediction models rely on empirical methods. It's noteworthy that several models, like the SAPPHIRE and ESP models, are accessible through the ESA-SPENVIS website.

Galactic cosmic rays, with energies ranging from hundreds or less of MeV up to TeVs, are mostly responsible for damages due to SEEs in satellite subsystems mostly through the electronic stopping power process (e.g., see Section on Effects of solar modulation on particle flux per unit area as a function of particle energy or electronic stopping power/restricted energy loss per unit length, i.e., on TID and SEE of the SR-NIEL Framework: Physics Handbook). Initially, the GCR transport through the heliosphere was addressed by Parker in the passage of energetic charged particles through interplanetary space (1965). In fact,  the Parker Transport Equation, or Parker Equation, describes (1) the GCR diffusion by magnetic irregularities, (2) adiabatic energy changes related to cosmic radiation expansions and compressions, (3) the convection effect resulting from the solar wind velocity, and (4) drift effects linked to drift velocity. Drift velocity, crucially determined by the antisymmetric part of the diffusion tensor, depends on charge and Sun magnetic polarity configuration.
In recent years, significant advancements in solving the Parker Equation emerged largely exploiting observation data from balloon flights and dedicated spectrometers on space-borne missions like PAMELA and AMS-01 missions (e.g. see Bobik et al., Systematic Investigation of Solar Modulation of Galactic Protons for Solar Cycle 23 Using a Monte Carlo Approach with Particle Drift Effects and Latitudinal Dependence (2012) and references therein), as well as utilizing the unprecedented measurement accuracy of spectra from the AMS-02 experiment on the ISS since 2011, complemented by observations from Ulysses spacecraft and Voyager probes up to the heliosphere boundary (e.g., see Boschini et al., The HELMOD model in the works for inner and outer heliosphere: From AMS to Voyager probes observations (2019) and references therein). At low energies, GCR intensities are significantly affected by time-dependent solar modulation, with the modulation effect diminishing to several percent at around 10 GeV/nucleon (Figs. 9-10 of Boschini et., Inference of the Local Interstellar Spectra of Cosmic-Ray Nuclei Z < = 28 with the Galprop-HelMod Framework (2020) and references therein). 
To evaluate its suitability for space radiation environment applications, the HelMod model underwent a comprehensive comparison with commonly employed solar modulation models — namely, CREME96, CREME2009, ISO-15390, and BON2020 — using the complete set of experimental data from AMS-02. The HelMod model exhibited good to superior agreement with respect to the other models across the full range of experimental data provided by AMS-02 (Boschini et al., The transport of galactic cosmic rays in heliosphere: the HelMod model compared with other commonly employed solar modulation models (2022); see also this web page). The ISO-15390 model, as outlined by the European Cooperation for Space Standardization guideline ECSS on Space Environment: Technical Report ECSS-E-ST-10-04C (2020), is currently recommended for evaluating galactic cosmic rays' spectral fluences within the space radiation environment framework. Moreover, the reliability of the HelMod model extends to energy levels below those observed by AMS-02 (e.g., see Fig. 6 of S.Bartocci et al., Galactic Cosmic-Ray Hydrogen Spectra in the 40–250 MeV Range Measured by the High-energy Particle Detector (HEPD) on board the CSES-01 Satellite between 2018 and 2020 (2020), data from CSES-01 Satellite) and compared with data at solar distances less than 1 AU (e.g., see Fig. 3 of Rankin et al., Anomalous Cosmic-Ray Oxygen Observations into 0.1 au (2022), data from NASA's Parker Solar Probe mission). At present, differential fluxes from the HelMod Model, along with their short- and long-time forecasts at any heliospheric location (e.g., see Boschini et al., Forecasting of cosmic rays intensities with HelMod Model (2022); see also this webpage), are readily accessible on the HelMod website. Additionally, the Local Interstellar Spectra of galactic cosmic rays with Z<=28 (as illustrated in Fig. 8 of Boschini et., Inference of the Local Interstellar Spectra of Cosmic-Ray Nuclei Z < = 28 with the GalProp-HelMod Framework (2020)) resulting from the collaborative GalProp-HelMod initiative (e.g., also referred to as GalProp-HelMod join effort), can be found on the same website. It has to be remarked that, as discussed by Boschini et al. (2024), the contribution of ultra-heavy galactic cosmic ray ions (UHGCRs, i.e., GCRs with Z>28) to the radiation hazard in space, such as the SEE rate, is expected to be negligible (see also this webpage).
Currently, the HelMod code relies on HelMod-4/CUDA, which is a GPU-accelerated method for solving the Parker Equation (e.g., see M J Boschin et al., Fast and accurate evaluation of deep-space galactic cosmic ray fluxes with HelMod-4/CUDA, Advances in Space Research (in press), April 2024). It exploits an NVIDIA GPU farm developed under ASIF program. The code is an evolution of the HelMod-4 code, porting the algorithm to GPU architecture using the CUDA programming language. This approach achieves significant speedup compared to a CPU implementation. The HelMod-4/CUDA code (e.g., see this webpage) has been validated by comparing its results with the most precise and updated experimental GCR spectra observed during high and low solar activity periods, both in the inner and outer heliosphere, at the Earth location, and outside the ecliptic plane. The comparison shows that HelMod-4 and HelMod-4/CUDA can be equivalently used to provide solar-modulated spectra with a similar degree of accuracy in reproducing observed data.

During periods of solar activity close to the minimum, it is expected that 1) there will be reduced emissions of solar energetic charged particles, while 2) galactic cosmic ray intensities will increase, particularly concerning the lower energy part of their omnidirectional distributions.

Finally, it is worth noting that charged particles also are streaming from Jupiter’s magnetosphere and its radiation belts. The distance between Jupiter and Earth ranges from 4.2 to 6.2 AU. Despite this, Jupiter could still serve as a relevant source of low-energy electrons in the inner heliosphere (e.g., see Gogt et al., Jovian electrons in the inner heliosphere (2018)). However, the validity of models available in SPENVIS does not extend typically beyond distances of about 100 Jupiter radii.

The solar energetic charged particles induce (as already mentioned) both ionizing (TID) and non-ionizing (NIEL or TNID) cumulative doses in the sensitive components used in satellite subsystems and instrumentation. The deposited TID and TNID doses due to GCRs are usually expected to be less relevant. However, GCRs are a major source of SEEs, single-event effects in devices sensitive to this type of radiation damage.
As previously illustrated, there are approximated and/or statistical models available for SEP spectral fluences, several are accessible via ESA-SPENVIS website. Therefore, one needs to derive (within suitable approximations) the spectral fluences for each type of charged particle (i.e., electrons, protons, and nuclei/ions dealt previously) emitted from the Sun and those propagated through the heliosphere, finally impinging on satellite devices after traversing spacecraft walls. The expected TID and TNID doses are estimated utilizing the residual spectral fluence for each type of charged particle, i.e., the spectral fluences emerging from the spacecraft walls (then impinging on the devices under investigation) and combining them with electronic and displacement stopping powers, respectively. Meanwhile, for each device sensitive to SEE damage, the expected number of SEEs is estimated by combining the measured SEE cross-section (for the current device under investigation) with GCRs' residual spectral fluences and the corresponding electronic stopping power in the device material.
Due to the relatively low energies of SEP spectral fluences, TID doses are sufficiently well estimated using the electronic stopping power in the device medium. For example, one can obtain this information from the SRIM code for massive charged particles (i.e., protons and nuclei/ions) and, for electrons, from ESTAR tables at NIST (National Institute of Standards and Technology). These data for electrons, protons and nuclei/ions are also available on the  SR-NIEL website from the web calculators section: Electronic Stopping Power Calculators (and TID doses) for protons, ions and electrons; Radiative Stopping Power for electrons. With regard to the deposited NIEL doses (or TNID doses), it's worth noting that tables' availability for displacement stopping power (or NIEL) is limited in the literature. However, since 2014, these latter can be obtained for materials and compounds from SR-NIEL web calculators, particularly in the section SR-NIEL Calculators and TNID doses. They are also accessible via ESA-SPENVIS website (including those dedicated to solar cells).
The unprecedented measurement aaccuracy of the AMS-02 experiment associated with data collected during more than a decade has significantly expanded our past knowledge of GCRs fluences at high energies, well beyond the corresponding tabulated values of the electronic stopping power from the SRIM code (e.g., see Case study on SEEs employing the restricted energy-loss and dependence on solar modulation model in the  SR-NIEL Framework: Physics Handbook). Additionally, for particle energies approaching or above the ionization minimum, the actually deposited energy in a medium may be lower than that dealt from the electronic stopping power due to emitted delta-rays not being fully absorbed (i.e., the restricted energy-loss has to be accounted for). At very high energy, this effect cannot be neglected anymore (e.g., see Particle flux per unit area as a function of particle energy or electronic stopping power/restricted energy loss per unit length, and relevance of solar modulation effects and Restricted energy-loss for cumulative (e.g., TID) and non-cumulative (e.g., SEE) energy deposition effects within SR-framework). Currently, the SR-NIEL website includes the so-called SR-framework electronic stopping power treatment, which extends the energy ranges covered by SRIM up to ultra-high energies. The related web calculators are available in the already mentioned section Electronic Stopping Power Calculators (and TID doses) for protons, ions and electrons; Radiative Stopping Power for electrons. A further web calculator section is dedicated to Restricted Energy-Loss (and TID doses) Calculators within SR-framework of electronic stopping poweRestricted Energy-Loss (and TID doses) Calculators within SR-framework of electronic stopping power. In addition, under the ASIF program, for each species of GCRs experienced during a space mission, the HelMod website provides their spectral fluence via the transfer orbit calculator for GCRs intensities, as well as from SR-NIEL website (see also this webpage) one dedicated to missions at 1 AU, with a table reporting Data Base Current Availability in HelMod website: the spectral fluence of the selected cosmic rays species (with low energy limit indicated here) can be used with the SEE Calculators in SR-NIEL. The HelMod model, as previously illustrated, has forecasting capabilities and fully reproduces AMS-02 data at high energies. Finally, once the Single Event Effect (SEE) device cross-section is available/measured, one can obtain the approximately expected number of SEEs utilizing the SR-NIEL website for the cases of planar or isotropic spectral GCRs fluences.

Further details on space radiation environment can be found, for instance, in Sect. 8.2 (titled Space Radiation Environment, pages 582-645)  of Leroy and Rancoita, Principles of Radiation Interaction in Matter and Detection (2016) (and references therein). Models/topics are available at ESA-SPENVIS website and  ASIF related websites of ASIF program. Moreover, additional pieces of information and treatments regarding electronic stopping power, displacement stopping power (NIEL), and SEEs are available in various chapters (e.g., Chapts. 2, 7 and 11) of the above mentioned book with the inside cited relevant literature, as well as in the complementary SR-NIEL Framework: Physics Handbook.

Scientific and Technological Activities, Tool Developments for ASIF Space Radiation Environment (ASRE) activities and ASIF related websites

(following ASIF implementation agreements 2017-15-HD.0 ASI-INFN, 2021-36-HH.0 ASI-UNIMIB and 2024-21-HH ASI-INFN)

Particle transport and interaction

• SR-NIEL Framework: Physics Handbook
• SR-NIEL Web Calculators
• Geant4 and SR embedded treatment
• Restricted energy-loss treatment within SR-NIEL framework for dealing with particle energy deposition in a medium
• Impact of solar modulation on particle flux per unit area as a function of particle energy or electronic stopping power or restricted energy loss
• LET distributions for Fe-ions from SPENVIS, CREME and SR-NIEL/HelMod-4 frameworks: dependence of the estimated number of SEE on solar modulation model
• Case studies on TID and SEEs when restricted energy-loss is employed with respect to the usage of electronic stopping power
• Case study on SEEs employing the restricted energy-loss and dependence on solar modulation model
• Currently available SR-NIEL–7 web calculators

Forecasting and transport of GCRs in heliosphere

• HelMod-4 Model
• Modulated spectra of cosmic rays ion with Z up to 28 from GalProp-HelMod join effort
• Cosmic Rays in the Heliosphere and HelMod-4 Model
• HelMod-4 forecasting of cosmic rays
• HelMod-4, the solar modulation model of galactic cosmic rays employed within SR-NIEL framework: comparison with AMS-02 data and other commonly employed modulation models
• Impact of ultra-heavy GCR ions (e.g., with Z>28) on the overall expected SEE rate
• Predicting Galactic Cosmic Ray Intensities with HelMod-4 Model: Transfer Orbit Fluences at any Orbital Trajectory inside the Heliosphere
• HelMod-4 Model based web calculator for the cosmic rays fluence along a transfer orbit in deep space missions
• Currently available HelMod web calculators
• HelMod-4/CUDA and GPU-Farm

Magnetosphere transport models

• Comparison between geomagsphere model (gm) and magnetocosmics-magnetospheric shielding model (MSM)
• Geomagsphere model and web available calculators 

Space Radiation Environment and ASIF related websites

• www.sr-niel.org   or   www.sr-niel.asi.it
• www.helmod.org   or   www.helmod.asi.it
• www.geomagsphere.org   or   www.geomagsphere.asi.it

People involved in space radiation environment activities within ASIF

• Who in ASIF space radiation environment activities and tools