Numerical study of proton acceleration at interplanetary shocks for the interpretation of the HENON CubeSat mission measurements

The HENON CubeSat mission is designed to fly on a distant retrograde orbit (DRO) around the Earth at about 0.1 Earth radii, for advance time space weather monitoring. The mission has a set of instruments which include an energetic particle detector measuring protons from a few MeV to hundreds of MeV. In this work, we investigate under what conditions energetic particles can be accelerated at interplanetary shocks above the detection threshold of about 2 MeV of the HENON instrument.
We set up a test particle numerical simulation in which protons move in the drift approximation around a shock transition, and are accelerated each time they cross the shock. Protons are injected at the shock with an energy of few tens of keV and are scattered in pitch angle by a collision operator. In the simulation, we vary the pitch-angle scattering time, the shock compression ratio, and the type of transport, which can be either normal diffusion or superdiffusion. In the superdiffusive case, a power-law distribution of scattering times is generated in order to reproduce a Levy walk. The proton energy spectra are obtained as a function of the elapsed time, keeping in mind that for strong heliospheric shocks associated to fast coronal mass ejections, the shock lifetime is of the order of one or two days. Several runs are carried out in order to determine (i) the parameter domain which leads to efficient acceleration and (ii) which runs lead to the highest energies. For typical parameters, superdiffusive acceleration turns out to be faster in accelerating protons. Simulation results will be presented for a wide parameter range, and we find that energies in the range of 2-10 MeV can be reached in a number of cases. 
This work was funded by the Italian Space Agency (ASI) through the Argotec contracts, numbers ARG-IT-CON-P-HEN-220002 and ARG-IT-CON-P-HEN-250003. GZ, SP, and GP acknowledge partial support by the Italian PRIN 2022, project 2022294WNB entitled "Heliospheric shocks and space weather: from multispacecraft observations to numerical modelling” (CUP H53D23000900006).