The aim of the workshop is to bring the nuclear astrophysics community together to discuss opportunities available at the ATLAS facility, to foster new collaborations, and solicit new ideas for future advancement of the facility and experimental program. The ATLAS facility has undergone an expansion in its capabilities to produce and study isotopes of astrophysical interest, both through facility enhancements (CARIBU, RAISOR, the soon-to-be N=126 factory, etc.) and experimental devices/techniques (MUSIC, HELIOS, ion trapping, GRETINA, GAMMASPHERE, etc.).

MICRA, which stands for Microphysics In Computational Relativistic Astrophysics, is a biennial workshop focused on improving, discussing, and addressing the microphysics needs of relativistic simulations of astrophysical systems, core-collapse supernovae, compact object mergers, and gamma-ray bursts by bringing together nuclear and neutrino theorists and astrophysicists and computational modelers. This year marks the 5th installment and the 10th anniversary of MICRA, and the first since the revolutionary gravitational wave event GW170817.

The beginning of the stellar era in the Universe is a singularly fascinating phase in the history of the Cosmos. The baryonic material filling the Universe at that time, having a composition inherited from Big Bang nucleosynthesis, has its physical characteristics modified by the very first stars. Indeed, the first stars will change the degree of ionized material in their vicinity, and, through their winds and/or supernova explosion, will inject energy, momentum, and newly-synthesized elements.

Nuclear physics is the necessary link between astronomical observations, stellar models and galactic chemical evolution. The impressive progress in astrophysics during the last decades explaining and predicting astronomical scenarios was only possible because of the fruitful interplay between all disciplines. New insights in one field triggered new developments in the other fields. New experimental techniques are typically the response to new predictions and observations.

Transitions mediated by the weak interaction play important roles in a wide variety of astrophysical phenomena. The accurate description of beta decays and electron captures are necessary for modelling the evolution of stars, the description of nucleosynthesis upon their cataclysmic demise, for example in neutron-star mergers and core-collapse supernovae, and the interpretation of multi-messenger signals from such events. A wide variety of β-decay and electron-capture (EC) data are needed for use in astrophysical modelling.

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Radioactive nuclei play a significant role in many current astrophysical quests. From the origin of the elements through the driving of the emissions from supernovae (56Ni) and kilonovae (r-process radioactivity), they are crucial for direct studies of galactic enrichment (7Be, 26Al, 44Ti, 60Fe, 99Tc, 244Pu, ...) and for new insights on stellar explosions (56/57Ni, 44Ti).