Characterization of Solar Energetic H and He Spectra Measured by the Energetic Particle Telescope (EPT) On-Board PROBA-V During the January 2014 SEP Event

Abstract

On January 6, 2014 a Solar Energetic Particle (SEP) event started that led to a 1030 cm $^{-2}$ $\text{s}^{-1}$ sr $^{-1}$ peak flux of E > 10 MeV protons on January 9, 2014 at geosynchronous orbit, an event exceeded only by about 15% of all SEP events. Such high flux events contribute the most to solar event-induced radiation effects in space equipment, while being easy to characterize based on data acquired by spectrometers, such as the EPT. The EPT instrument provides fluxes of electrons (0.5–20 MeV), H (9.5–300 MeV) and He (38–1200 MeV) ions. It presently flies on the PROBA-V satellite, launched into a Low Earth Orbit on May 7, 2013. As it has been reported that the He contribution to Total Non-Ionizing Dose (TNID) may be comparable to that of H in representative space environments, a data analysis to identify periods of high He flux as compared to H, and conditions under which both ions must be accounted for during radiation effect analyses, was performed. From the study of the positional variation of solar H and He fluxes, a formulation of the minimum L-value reached by these particles for a given rigidity is provided. The shape of solar H and He energy spectra as well as the H/He fluence ratio and pitch angle distributions are characterized. The contribution of He compared to H for Total Ionizing Dose (TID) and TNID effects is below 5% for devices shielded by >2mm Al.