A commercial magnetohydrodynamic (MHD) simulation package USIM is used to simulate two colliding plasma bubbles,which are not moving in the same horizontal line along the X direction.One similar experiment is performed on Shenguang Ⅱ laser facility,in which four laser beams each with a wavelength of 0.351 μm,total energy of 1.0 kJ,pulse duration of 1ns,are irradiated on an A1 target with a thickness of 50 μm.Every two beams constitute one 150-μm-diameter focal spot with an intensity of 1015 W/cm2.The X-ray radiation results show the asymmetric and peach-like plasma bubbles,which are different from the results obtained before, Here we report the possible reason for the asymmetric and peach-like structure in experiment.External magnetic field on the order of 1 T is chosen to perform the simulations,which could be a possible applied B field in future experiments performing on the Shenguang Ⅱ laser facility.In the simulations,different cases,especially the effects of different directional external magnetic fields,are consid-ered.When the reversal directional magnetic fields are embedded in the Y direction,the magnetic field lines are frozen in the plasma bubbles,moving and approaching to each other gradually with the magnetic field lines.The change of the direction of magnetic field lines in the interaction region indicates that the magnetic reconnection has been happened.The outflows between two plasma bubbles in the experimental result could be explained by magnetic reconnection,which can efficiently convert stored magnetic energy into kinetic energy and thermal energy by accelerating and heating plasma particles.The density jump at the position of the bow structure indicates the generation of shock waves,where the velocity of flow v is also larger than the sound speed vs.When the same directional attractive magnetic fields are embedded in the Y direction,magnetic field lines are piled up in the central part,where the magnetic field density is high,which indicates that the magnetic repulsion has been happened.Magnetic repulsion also delays the colliding between two plasma bubbles.The shock waves each with a width of 4 μm are also found in this case.The X-ray images in experiment and the density images in simulations show the similar peach-like structures,where the density results could be used to explain the X-ray radiation result for,I(v,Te) o∝ ρ2/√Tee(-hv/kTe),I is the radiation intense,v is the plasma velocity,Te is the electron temperature,p is the plasma density.Magnetic reconnection is the possible reason for the asymmetrical and peach-like structure in the experiment by comparing all kinds of simulation cases.The present simulation results will be of benefit to the future designing of experimental setup on the Shenguang Ⅱ laser facility,although a two-fluids model is needed to build a spontaneous magnetic field for the real plasma bubbles.%利用商用磁流体力学模拟程序USIM对双等离子体团相互作用过程进行了数值模拟,分别考察和比较了双对流等离子体团在外加磁场和无外加磁场情况下,相互作用的物理过程.发现在外加磁场情况下等离子体团相互作用会伴随着磁重联(反向磁场)、磁排斥(同向磁场)以及一些不稳定过程.针对激光产生等离子体团错位相互作用实验,进行了标度模拟,发现外加磁场起着重要作用,进一步表明激光等离子体的磁化特征.研究结果为下一步在神光Ⅱ激光装置进行强磁环境下等离子体实验提供理论指导.
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