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Magnetic reconnection is a primary driver of particle acceleration processes in space and astrophysical plasmas. Understanding how particles are accelerated and the resulting particle energy spectra are among the central topics in reconnection studies. We review recent advances in addressing this problem in nonrelativistic reconnection that is relevant to space and solar plasmas and beyond. We focus on particle acceleration mechanisms, particle transport due to 3D reconnection physics, and their roles in forming power-law particle energy spectra. We conclude by pointing out the challenges in studying particle acceleration and transport in a large-scale reconnection layer and the relevant issues to be addressed in the future. [ABSTRACT FROM AUTHOR]

For nanosecond pulsed gas discharge under hundreds of kV/cm in sulfur hexafluoride (SF6), the electric field emission (EFE) effect may be the mechanism of the initial electrons. Electrode surface micro-protrusions (ESMPs) generated after discharging, would affect the discharge process under a high electric field. To investigate the effect of ESMPs on the breakdown time delay and jitter, the breakdown characteristics of different electrode materials and surface roughness are determined in this paper. Three types of electrode materials include stainless 304L, EDM-AF5 graphite, and CuW70 W-Cu alloy. The influences of stainless 304L electrodes with surface roughness coefficients of 1.6 and 0.8 on the breakdown delay and jitter are compared. After 700 discharge shots, the morphology characteristics and distributions of ESMPs are observed by a contourgraph. Based on the statistical results of ESMPs and EFE theory, the relationship between the electric field of EFE and ESMPs can be calculated. In addition, the effective electron rates of negative ion detachment (NID) are estimated. The experimental and calculation results indicate that the initial electrons are mainly produced by the EFE effect. When the pressure is below 0.5 MPa, the NID effect is limited and the breakdown time delay and jitter are dependent on the height to radius ratio and distributions of ESMPs. Once the pressure exceeds 0.5 MPa, the NID effect will be significant and the influence of ESMPs can be neglected. [ABSTRACT FROM AUTHOR]

Magnetic reconnection in strongly magnetized astrophysical plasma environments is believed to be the primary process for fast energy release and particle energization. Currently, there is strong interest in relativistic magnetic reconnection in that it may provide a new explanation for high-energy particle acceleration and radiation in strongly magnetized astrophysical systems. We review recent advances in particle acceleration and reconnection physics in the magnetically dominated regime. Much discussion is focused on the physics of particle acceleration and power-law formation as well as the reconnection rate problem. In addition, we provide an outlook for studying reconnection acceleration mechanisms and kinetic physics in the next step. [ABSTRACT FROM AUTHOR]

Various systems can be modeled as a point-like explosion of ionized debris into a magnetized, collisionless background plasma—including astrophysical examples, active experiments in space, and laser-driven laboratory experiments. Debris streaming from the explosion parallel to the magnetic field may drive multiple resonant and non-resonant ion–ion beam instabilities, some of which can efficiently couple the debris energy to the background and may even support the formation of shocks. We present a large-scale hybrid (kinetic ions + fluid electrons) particle-in-cell simulation, extending hundreds of ion inertial lengths from a 3D explosion, that resolves these instabilities. We show that the character of these instabilities differs notably from the 1D equivalent by the presence of unique transverse structure. Additional 2D simulations explore how the debris beam length, width, density, and speed affect debris–background coupling, with implications for the generation of quasi-parallel shocks. [ABSTRACT FROM AUTHOR]

In this paper, the evolution and dynamics of anode plasmas in high-power hollow cathode diodes were studied by particle-in-cell (PIC) simulation. The simulation results show that the ion flow emitted by the anode plasma layer and the increase of the electron current caused by the ion flow will cause a significant decline in the diode impedance in a short time. In addition, the expansion of the anode plasma layer will cause the diode impedance to decrease. The PIC simulation technique is also applied to a high-power hollow cathode diode of a 1.0 MV-LTD generator for anode plasmas, and the PIC simulation results were compared with the experimental data. [ABSTRACT FROM AUTHOR]

Surface evolution for a conductor electrode under pulsed megagauss (MG) magnetic field was investigated. Stainless steel rods with 3 mm diameter were driven by 8 MA, 130 ns (10%–90%) current pulse in a series of shots on the Primary Test Stand. Experimental data from two complementary diagnostic systems and simulation results from one-dimensional magneto-hydrodynamics code reveal a transition phase for instability development. The transition, which begins as the conductor surface starts to expand, lasts about 40 ns in the pulse. It ends after the thermal plasma is formed, and striation electrothermal instability growth stops but magneto-Rayleigh-Taylor instability (MRTI) starts to develop. An expanding velocity which grows to about 2.0 km/s during the transition phase was directly measured for the first time. The threshold magnetic field for thermal plasma formation on the stainless steel surface was inferred to be 3.3 MG under a rising rate of about 66 MG/μs, and after that MRTI becomes predominant for amplitude growth in surface perturbation. [ABSTRACT FROM AUTHOR]