Researchers from the Institute of Modern Physics (IMP) of the Chinese Academy of Sciences (CAS) and their collaborators have obtained new results on key atomic processes of solar coronal mass ejections. They precisely measured the quantum‑state population in collisions between highly charged nitrogen ions and helium atoms, providing benchmark data for more accurate modelling of space and astronomical observations. Their findings were published in The Astrophysical Journal Supplement Series on June 8.

Coronal mass ejection is an extreme space weather phenomenon involving massive release of charged ionic matter and energy triggered by intense solar activity. It can trigger severe geomagnetic storms and seriously disrupt satellite communications, navigation systems and the stability of power grids. Highly charged ions ejected during coronal mass ejections undergo charge‑exchange reactions with neutral particles in the Earth's magnetosphere, emitting characteristic X‑rays. Therefore, precise modelling of observed X‑ray spectra is an indispensable approach to trace the chemical composition, solar activity characteristics and internal information of the Sun behind coronal mass ejections.

Nevertheless, the lack of precise atomic data and insufficient understanding of the microscopic mechanism of highly excited states in charge‑exchange reactions have long limited human understanding of coronal mass ejection events.

In this study, utilizing the 320 kV platform for multi-disciplinary research with highly charged ions in Lanzhou, China, the researchers adopted an innovative strategy to directly measure excited quantum‑state populations. They quantified the highly excited‑state populations in collisions between neutral helium gas and highly charged nitrogen ions (N⁶⁺), a key species in coronal mass ejections.

"The experiment offered benchmark cross‑sections for quantum‑state populations and resolved discrepancies among previous theoretical calculations, a finding that is of significance for advancing close‑coupling theoretical methods in atomic collision research," said Dr. ZHANG Ruitian from IMP, the first and corresponding author of this study.

The study also revealed that the experimentally measured double‑excited‑state populations contribute considerably to the soft X‑rays observed during coronal mass ejection events. The experimental methodology developed in this work is applicable to future laboratory astrophysics research.

The research was jointly accomplished by IMP, Beijing Institute of Applied Physics and Computational Mathematics, Shenzhen Technology University, High Energy Accelerator Research Organization (Japan), National Astronomical Observatories of CAS, Netherlands Space Office, Technion‑Israel Institute of Technology, Tianjin University and Eckerd College (USA).

DOI: https://doi.org/10.3847/1538-4365/ae690d

Figure. Dependence of quantum state population on the collision energy. (Image from IMP)