Researchers Obtain New Results on Solar Wind Ion Charge Exchange (Planetary Science)

Researchers at the Institute of Modern Physics (IMP) of the Chinese Academy of Sciences (CAS) and their collaborators have recently obtained new results on the solar wind ion charge exchange. The results were published in The Astrophysical Journal Supplement Series

Charge exchange is one of the important mechanisms of soft X-ray emission in many celestial environments. Soft X-rays caused by charge exchange are important basic data for diagnosing plasma evolution and celestial plasma modeling, which can be used to study the temperature, abundance, and ion species of solar wind ions or stellar wind ions, and help us gain an in-depth understanding of celestial plasma and fusion.  

At present, in charge-exchange soft X-ray emission modeling, researchers usually apply the semi-classical theories to calculate the cross-section data of the state-selective capture resolved by the principal quantum number n and the angular quantum number l. However, the accuracy of the model urgently needs to be verified.  

In this study, the researchers used Reaction Microscopy to systematically measure the state-selective charge exchange of Ne(8,9)+ ions with He and H2 in the solar wind speed range, and obtained the cross-section data of the main quantum number resolution of the electron captured to the projectile ion.

Fig. 2. The normalized emission spectra of Ne7+ following single electron capture between 4 keV/u Ne8+ and He. The solid lines show the reconstructed X-ray spectra from different angular momentum models; The solid square symbol indicates the other group measured X-ray spectra. (Image from The Astrophysical Journal Supplement Series)

They then compared the experimental data with the results calculated by the multi-channel Landau-Zener method and found that the main reaction channels were consistent with theoretical expectations. 

Meanwhile, by applying charge exchange models commonly used in astrophysics, the researchers obtained the angular quantum number resolution cross-sections corresponding to different angular quantum number distribution models, developed relevant calculation programs, and obtained soft X-ray spectra in the charge exchange between Ne8+ and He atoms.

Moreover, they compared reconstructed X-ray spectra with the existing X-ray measurement spectrum and found that there were significant differences in different angular momentum distribution models, which tested the applicability of the angular momentum distribution model in astrophysics. 

This work was supported by the Key R&D Program of the Ministry of Science and Technology, the Strategic Priority Research Program of CAS, and the National Natural Science Foundation of China. 

Featured image: The measured Q-value spectra for the single electron capture in Ne8+-He collisions at different projectile velocities. (Image from The Astrophysical Journal Supplement Series)

Reference:  J. W. Xu et al., “Measurement of n-resolved State-selective Charge Exchange in Ne(8,9)+ Collision with He and H2“, 2021 ApJS 253 13.

Provided by Chinese Academy of Sciences

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