We report experiments characterizing the stratified and filamentary structures formed in the dense core of nanosecond electrical explosion of aluminum wires to understand the physical scenario of electrothermal instability. Direct experimental observations for stratification and filamentation instabilities, as well as the coexistence state of azimuthal strata and vertical filament in the dense plasma column, are presented. The wire core exhibits remarkable different patterns of instability with the decreasing wire length. The shadowgram of shorter wires demonstrates that the instability is transformed from stratified structures to filamentary structures. According to a radial magnetohydrodynamic computation, the wire enters a phase state of negative temperature dependence of resistivity before voltage breakdown. However, filamentary structures are only observed in exploding wires of 1 cm and 0.5 cm in length. The analyses based on experimental and computational results indicate that the increase in internal energy determines the manifestation of instability in the dense core. Filamentation instability occurs when the total energy input is no less than 1.5 times the vaporization energy at the moment of voltage breakdown. The lower limit of energy deposition ensures that the increase in internal energy covers vaporization energy.

中文翻译：

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爆炸丝密芯中的分层和成丝不稳定性

我们报告了表征在铝线纳秒电爆炸的致密核心中形成的分层和丝状结构的实验，以了解电热不稳定性的物理场景。介绍了分层和细丝不稳定性的直接实验观察，以及致密等离子体柱中方位地层和垂直细丝的共存状态。随着线长度的减少，线芯表现出显着不同的不稳定性模式。较短线的阴影图表明不稳定性从分层结构转变为丝状结构。根据径向磁流体力学计算，导线在电压击穿之前进入电阻率负温度依赖性的相状态。然而，仅在 1 厘米和 0.5 厘米长的爆炸丝中观察到丝状结构。基于实验和计算结果的分析表明，内能的增加决定了致密核心不稳定的表现。当总能量输入不小于电压击穿时汽化能的1.5倍时，就会出现丝状不稳定。能量沉积的下限确保内能的增加覆盖汽化能。电压击穿瞬间汽化能的5倍。能量沉积的下限确保内能的增加覆盖汽化能。电压击穿瞬间汽化能的5倍。能量沉积的下限确保内能的增加覆盖汽化能。