On December 18, Dr. ZHU Bojing and his research team from Sun Yat-sen University, University of Chinese Academy of Sciences, Key Laboratory of Computing Geodynamics of Chinese Academy of Sciences, and Columbia University published their research in Applied Mathematical Modelling, in two-paper series titled “Relativistic HPIC-LBM and its Application in Large Temporal-spatial Turbulent Magnetic Reconnection”.

These two papers provide a novel numerical scheme based on statistical mechanics for investigating the self-generated turbulence by magnetic field and plasma motion collective interaction in CKFC LTSTMRs

 In order to understand the role of turbulence in these relativistic resistive regions, it is important to understand visually and graphically. The mechanism of the magnetic energy release conversion, plasma heating and charged particle energization-acceleration in the CKFC LTSTMRs. Until now, the role of turbulence in these processes has been an open question that has been fiercely debated because of lack of high-resolution numerical simulations, which must be integrated long enough in time. To accomplish these lofty goals, researchers have resorted to employ the utmost resources from Tianhe-II supercomputer system in Guangzhou.

Solar atmosphere activities (SAA; e.g., limbs, flares, CMEs and so on), which are the most important phenomenon in the solar and Sun-Earth space systems are typical LTSTMRs and possess the following characteristics:

Multicomponent. There are several chemical compositions in the solar atmosphere that are dominated by hydrogen and helium, but these components constitute only a small percent of the total mass. In solar physics, scientists identify all the components as metals except hydrogen and helium, even though elements such as carbon and oxygen are included, which are not commonly considered to be metals.

Different degree of ionization. The plasma of the SAA includes partially and fully ionized plasma, and different layers have different thicknesses, temperatures and degrees of ionization.

Relativistic plasma. Observations show that the accelerated electron and ion particles reach relativistic energies in solar atmosphere LTSTMR activities.

CKFC physics process. Observations show that the SAA include many kinetic scale fractal and turbulence magnetic structures and are typical CKFC LTSTMRs.

All these demonstrates that the LTSTMRs in SAA are very complicated, and many of the physical pictures are still unclear or controversial, especially in the 3D LTSTMR self-generating-organization magnetic field region and self-feeding-sustaining plasma region.

To date, to the best of the authors' knowledge, there are no CKFC temporal-spatial scale physical and mathematical models, algorithms, or codes for investigating solar atmosphere LTSTMR.

In these two-paper, the team led by ZHU Bojng developed and validated the RHPIC-LBM (part I) and investigated the role of turbulence in the flux rope interaction (part II) on Tianhe-2 platform (from the National Supercomputer Center in Guangzhou, with 100,000 CPU cores, 120 CPU hours and 250 TB output per case). It must be pointed out that over 2000 cases were run in a period of 15 months. Such an accumulation of wall clock time on the Tianhe-II represents an astounding accomplishment in China and also in most western countries. The main discoveries are shown as follows:

Slipping MR exists in the adjacent magnetic field lines (MFLs) during the compress-stretch-slip process on the quasi-separatrix layers (QSLs and MFLs drastically change and form a linkage span) and the adjacent MFLs’ break-rejoin MR exists on the separatrix surfaces.

The slipping MR (first type MR) and the MFLs’ break-rejoin MR (second type MR) are closely linked with the oblique and resistive tearing instabilities, respectively. In the 3D model, the first type MR forms O-type null points, while the second type MR forms X-type null points. The magnetic energy conversion is dominated by turbulence-induced oblique instabilities in the 3D model instead of the resistive tearing instabilities in the 2.5D model.

Magnetic energy conversion occurs in the interaction of the plasmoid-to-flux rope, plasmoid-to-plasmoid, and flux rope-to-flux rope. The turbulent acceleration is an independent acceleration mechanism in LTSTMR, included by the interaction of waves-to-waves and waves-to-particles, which is different from the original hybrid acceleration mechanism.

Particles can be energized and accelerated at a longer time scale and can be accelerated to relativistic energies after being pre-accelerated by a Fermi-Betatron-shock wave acceleration process.

Note:

CKFC : Continuous kinetic-dynamic-hydro fully coupled (electron MHD; Hall MHD; ion MHD; hydro-physics).

LTSTRM: Large temporal-spatial scale turbulent MR (observed current sheet thickness to characteristic electron length ratios on the order of 1010~1011; observed evolution time to electron cyclotron time ratios on the order of 1010~1011).

Contact:

 ZHU Bojing, YNAO, CAS

bjzhu@ynao.ac.cn