Abstract Astrophysical jets play crucial roles in star formation and transporting angular momentum away from accretion discs, however, their collimation mechanism is still a subject of much debate due to the limitations of astronomical observational techniques and facilities. Here, a quasi-static toroidal magnetic field is generated through the interaction between lasers and a four-post nickel target, and our all-optical laboratory experiments reveal that a wide-angle plasma plume can be collimated in the presence of toroidal magnetic fields. Besides the confinement effects, the experiments show the jet can also be accelerated by the enhanced thermal pressure due to the toroidal magnetic fields compressing the flow. These findings are verified by radiation magneto-hydrodynamic simulations. The experimental results suggest certain astrophysical narrow plasma flows may be produced by the confinement of wide-angle winds through toroidal fields.
Abstract The origin of energetic charged particles in universe remains an unresolved issue. Astronomical observations combined with simulations have provided insights into particle acceleration mechanisms, including magnetic reconnection acceleration, shock acceleration, and stochastic acceleration. Recent experiments have also confirmed that electrons can be accelerated through processes such as magnetic reconnection and collisionless shock formation. However, laboratory identifying stochastic acceleration as a feasible mechanism is still a challenge, particularly in the creation of collision-free turbulent plasmas. Here, we present experimental results demonstrating kinetic turbulence with a typical spectrum k −2.9 originating from Weibel instability. Energetic electrons exhibiting a power-law distribution are clearly observed. Simulations further reveal that thermal electrons undergo stochastic acceleration through collisions with multiple magnetic islands-like structures within the turbulent region. This study sheds light on a critical transition period during supernova explosion, where kinetic turbulences originating from Weibel instability emerge prior to collisionless shock formation. Our results suggest that electrons undergo stochastic acceleration during this transition phase.
Abstract The hydrodynamic instability growth seeded by localized perturbations exerts a significant influence on the performance of inertial confinement fusion implosions. Direct-drive, planar target ablative hydrodynamic instability growth simulations were performed to study the evolution of localized perturbations at peak drive intensities of ignition designs. The study focused on hydrodynamic instability seeded by Gaussian bumps and rectangular pits on the target outer surface at a laser intensity of about $9 \times 10^{14} \, \rm W/cm^2$. The findings indicated that the nonlinear growth of localized perturbations is significantly influenced by nonlocal electron heat transport. It was observed that the small-scale Gaussian bump experiences a phase reversal before the target acceleration phase and evolves into an isolated bubble, with spikes growing obliquely on both sides tending to heal the void created by the bubble. Notably, nonlocal electron heat transport effects slow down void healing and nonlinear bubble growth, which can prevent defects from penetrating the target shell prematurely. For rectangular pits with larger lateral dimensions, no overall phase reversal occurs before target acceleration, and the nonlinear bubble growth is similarly suppressed.
These findings underscore the importance of considering nonlocal electron heat transport effects in multi-dimensional implosion simulations.
The ferromagnetic resonance overvoltage of power system often occurs for a long time, which seriously endangers the safe operation of electrical equipment and power grid.The feature extraction and recognition of ferromagnetic resonance overvoltage is helpful for taking targeted measures to restrain overvoltage quickly, and it is of great significance to guarantee electric power system running in reliable and steady status.Based on the analysing the over-voltage and over-current waveform characteristics of different resonance types by EMTP simulation software, a method of ferromagnetic resonance overvoltage recognition is proposed which is named earth capacitance and excitation inductance ratio.The theoretical foundation of this method is visualized, and a lot of actual data show that this method is feasible and effective in ferromagnetic resonance overvoltage recognition.
In astrophysics, relativistic magnetic reconnection, where particles can accelerate in a region of a strong electric field and weak magnetic field, is a key physical process for the explanation of high-energy photon synchrotron emission above 160 MeV, the limit given by the balance between the accelerating electric force and the radiation reaction force. However, the reconnection dynamics—more importantly, the particle acceleration and photon emission dynamics—in this radiation-dominated, relativistic regime have not been self-consistently investigated yet. In this paper, through theoretical derivation of the modified relativistic tearing instability (RTI) and kinetic particle-in-cell simulations, we find that, because of the radiation reaction, the compression of the reconnecting current sheet is significantly enhanced, leading to an increase in the RTI growth rate in the short-wavelength range. As a result, during reconnection, the current sheet is fragmented into a chain of many more magnetic null points separated by much smaller plasmoids, which eventually gives rise to significant improvement of particle acceleration efficiency and shortening of photon emission duration. In the simulations, prompt emission at duration ωpeΔT ≃ 233 (reduced by a factor of 3) of high-energy nonthermal photons with a hard power law of index 2.11 for photon energies <100 MeV and index 1.39 for those >100 MeV is observed. These characteristics are consistent with the observed emission properties of short gamma-ray bursts, particularly of GRB 090510, supporting the radiation-dominated reconnection scenario.
Abstract We discuss the formation of a Kelvin–Helmholtz instability (KHI) produced by a laser-driven thin separate plastic (CH) foil plasma. The experimental design consists of magnetized plasma driven by intense laser irradiation and a small cylindrical permanent magnet. By comparing situations with and without an external magnetic field, we found that the KHI showed different rolling features which could be effectively suppressed by an external magnetic field. A quantitative analysis shows the consistency between the experiments and theory.
Abstract The origin of magnetic fields and their amplification have always been hot topics in fields such as astrophysics and high-energy-density physics. Among them, the turbulent dynamo effect is an important candidate mechanism, and the interaction between supernova remnants (SNRs) is an important carrier for studying the amplification effect of turbulent magnetic fields. In this paper, we use the radiation magnetohydrodynamic simulation program to carry out a scaling simulation study on the amplification effect of turbulent magnetic fields in the interaction of SNRs driven by powerful lasers. We investigate and compare the evolution of turbulence under different laser driving methods, different directions, and different intensities of initial external environmental magnetic fields. Here, we carefully identify the contributions of Biermann self-generated magnetic fields and environmental magnetic fields in the process of magnetic field amplification, present magnetic energy spectra, and magnetic field amplification factors, and analyze the influence of radiative cooling effect on turbulence and magnetic field evolution. The results show that the collision direction component of the environmental magnetic field dominates the process of magnetic field amplification, and the frequency spectrum of turbulence is consistent with Kolmogorov's law. The research results are necessary for sorting out and elucidating the physical mechanism of magnetic field amplification in SNRs, and have reference significance for regulating turbulence in strong magnetic fields in the future.
Pillars of Creation, one of the most recognized objects in the sky, are believed to be associated with the formation of young stars. However, so far, the formation and maintenance mechanism for the pillars are still not fully understood due to the complexity of the nonlinear radiation magneto-hydrodynamics (RMHD). Here, assuming laboratory laser-driven conditions, we studied the self-consistent dynamics of pillar structures in magnetic fields by means of two-dimensional (2D) and three-dimensional (3D) RMHD simulations, and these results also support our proposed experimental scheme. We find only when the magnetic pressure and ablation pressure are comparable, the magnetic field can significantly alter the plasma hydrodynamics. For medium magnetized cases ($\beta_{initial} \approx 3.5$), {the initial magnetic fields undergo compression and amplification. This amplification results in the magnetic pressure inside the pillar becoming large enough to support the sides of the pillar against radial collapse due to pressure from the surrounding hot plasma. This effect is particularly pronounced for the parallel component ($B_y$), which is consistent with observational results.} In contrast, a strong perpendicular ($B_x, B_z$) magnetic field ($\beta_{initial} < 1$) almost remains its initial distribution and significantly suppresses the expansion of blow-off gas plasma, leading to the inability to form pillar-like structures. The 3D simulations suggest that the bending at the head of `Column \uppercase\expandafter{\romannumeral1}' in pillars of creation may be due to the non-parallel magnetic fields. After similarity scaling transformation, our results can be applied to explain the formation and maintenance mechanism of the pillars, and can also provide useful information for future experimental designs.
The kinetic effects of magnetic fields on the transport of relativistic jet in the intergalactic medium remain uncertain, especially for their perpendicular component. By particle-in-cell simulations, we find that when only jet electrons are fully magnetized, they are directly deflected by the magnetic field, but jet protons are mainly dragged by collective charge-separation electric field. However, when both electrons and protons are fully magnetized, the contrary is the case. Their balance tremendously distorts the jet density and electromagnetic fields, leading to enormous energy exchange between different species and fields. As a result, the electron spectrum energy distribution (SED) gets reshaped and the power law slope of the SED decreases as the magnetic field strength increases. In other words, we may infer that magnetic fields around the relativistic jet play a crucial role in shaping the observed SED.
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