Electronic dynamics in many-body system composed of atoms/molecules are of great importance in our daily life since high-tech applications such as semi-conductor, laser associates, bioscience, fuel chemical reactions and so on are, to a large extent, based on our knowledge of the dynamics of many-electron processes. Under APEX international cooperation, research topic in this direction is related to ion-atom collisions at collision energies ranging from 100 eV/u up to GeV/u, i.e., from the low velocity edge to the relativistic regime, where a large band of bare/dressed ions from proton to uranium ions, or even the corresponding neutral atoms [1], can be selected as projectiles to study ionization of the target, electron loss by structured projectiles, two-center dielectronic transitions, charge exchange processes in astrophysics & plasma[2], Coulomb explosion of molecules[3-5], creation of electron-positron pairs in a strong electromagnetic field of the colliding partners. Dedicated experimental terminals on the current HIRFL facility at Lanzhou have been well established and for the near future HIAF facility at Huizhou are proposed.

In these terminals a couple of high-resolution reaction microscopes (REMi) (shown in Fig. 1) are/will be used to obtain fully differential cross sections (FDCS) of the ultrafast ion collision processes, i.e., cross-sections differential in all observables (momenta) of the final state of the colliding system, enabling much more detailed studies of such processes and provide valuable information on the collision dynamics.  Integrations over any of these quantities(observables) will blur the clarity of investigations on the mechanism of corresponding collisions thus such FDCS provide by far the most stringent test for theory. Owing to its revolutionary improvements in both detection efficiency and accuracy of the REMi our knowledges about the few-body quantum dynamics have been significantly advanced in the field during the last two decades. Despite some activity during the last decades the field of relativistic collisions involving highly charged ions with light atoms remains largely unexplored. Besides the relativistic effects, in collisions with highly charged ions such as Zp/v ~ 1, at such strong electromagnetic field, one would expect significant deviations / discrepancies between nonperturbative and perturbative calculations. 

Fig. 1 reaction microscope

Another interesting topic which can only be studied via big storage ring facilities is the electron-positron pair creation/production in the supercritical field generated by two head-on colliding highly charged ions at energies close to the Coulomb barrier. The experimental exploration of this phenomenon would constitute a major breakthrough and an important test of the theory of quantum electrodynamics (QED) in the region of strong fields. In HIAF facility, a giant set of detector arrays dedicated to the subject have been thus proposed (Fig. 2).

Fig. 2 Detector arrays for atomic processes at extremes @ HIAF

[1]   Zhang, S. F.; Zhu, X. L.; Voitkiv, A. B.; Feng, W. T.; Guo, D. L.; Gao, Y.; Zhang, R. T.; Wang, E. L. & Ma, X., Mutual ionization in atomic collisions near the electronic threshold, Journal of Physics B: Atomic, Molecular and Optical Physics 2014, 47, 105202

[2]  Jiawei Xu, Xiaolong Zhu^*, Wentian Feng, Dongmei Zhao, Weizhe Huang, Dalong Guo, Yong Gao, Shaofeng Zhang, Xu Shan, Xiangjun Chen, Xinwen Ma^*, State-selective single-electron capture in 30-keV N3+–He collisions, X-Ray Spectrometry 49, 85–89

[3]  XiaoLong Zhu, XiaoQing Hu, ShunCheng Yan, YiGeng Peng, WenTian Feng, DaLong Guo, Yong Gao, ShaoFeng Zhang, Amine Cassimi, JiaWei Xu, DongMei Zhao, DaPu Dong, Bang Hai, Yong Wu*, JianGuo Wang and X. Ma*, Heavy N+ ion transfer in doubly charged N2Ar van der Waals cluster, Nature Communications, 11, 2987

[4]   S. Yan, P. Zhang, V. Stumpf, K. Gokhberg, X. C. Zhang, S. Xu, B. Li, L. L. Shen, X. L. Zhu, W. T. Feng, S. F. Zhang, D. M. Zhao, and X. Ma, Interatomic relaxation processes induced in neon dimers by electron-impact ionization, Physical Review A 97(1): 010701

[5] Zhang, S. F.; Fischer, D.; Schulz, M.; Voitkiv, A. B.; Senftleben, A.; Dorn, A.; Ullrich, J.; Ma, X. & Moshammer, R., Two-Center Interferences in Dielectronic Transitions in H_2^+ + He Collisions, Phys. Rev. Lett. 2014, 112, 023201