Production of runaway electrons and x-rays during streamer inception phase
Production of runaway electrons and x-rays during streamer inception phase
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DOI：
10.1088/1361-6463/acaab9
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发表时间：
2022-12
期刊：
影响因子：
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通讯作者：
L. Contreras-Vidal;C. Silva;R. Sonnenfeld
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文献类型：
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作者：
L. Contreras-Vidal;C. Silva;R. Sonnenfeld
流光在闪电通道的形成和传播中起着关键作用。在自然界中，飘带很少单独出现。它们的整体行为非常复杂，难以描述。例如，负闪电先导的流光区内复杂的动力学产生了空间干，这有助于推进步进先导。另一个例子是精灵形态复杂性的增加如何导致更高的精灵电流和更大的能量沉积在中间层。流光电晕的复杂动力学的见解可以从实验室实验中获得，使我们能够控制流光形成的条件。基于同步纳秒时间分辨率摄影，和测量的电压，电流和X射线发射，我们报告的负实验室流光在88千帕的大气中的特性。在6cm的点-面放电间隙中，在62.2 ± 3.8 kV的峰值电压下产生流光。虽然所有的放电驱动到相同的峰值电压，放电发生在不同阶段的相对缓慢的电压上升（177 ns），使我们能够研究放电特性作为一个函数的起始电压。起始电压范围在24和67 kV之间，但观察到X射线发射仅发生在53 kV以上，X射线爆发能量与电压成二次方。发现电流脉冲和X射线发射之间的平均延迟为3.5 ± 0.5 ns，表明逃逸电子是在流光初始阶段或不晚于过渡阶段产生的，此时初始云破裂成流光细丝。在这个短时间内，逃逸的电子可以穿过差距，撞击接地板并产生韧致辐射x射线光子。然而，流光本身不能跨越差距超过3.5 mm，这支持了逃逸电子产生与流光到接地电极的连接无关的想法。
Streamers play a key role in the formation and propagation of lightning channels. In nature streamers rarely appear alone. Their ensemble behavior is very complex and challenging to describe. For instance, the intricate dynamics within the streamer zone of negative lightning leaders give rise to space stems, which help advance the stepped-leader. Another example is how the increasing morphological complexity of sprites can lead to higher sprite current and greater energy deposition in the mesosphere. Insights into the complex dynamics of a streamer corona can be obtained from laboratory experiments that allow us to control the conditions of streamer formation. Based on simultaneous nanosecond-temporal-resolution photography, and measurements of voltage, current, and x-ray emissions, we report the characteristics of negative laboratory streamers in 88 kPa of atmosphere. The streamers are produced at peak voltages of 62.2 ± 3.8 kV in a point-to-plane discharge gap of 6 cm. While all discharges were driven to the same peak voltage, the discharges occurred at different stages of the relatively slow voltage rise (177 ns), allowing us to study discharge properties as a function of onset voltage. The onset voltage ranged between 24 and 67 kV, but x-ray emissions were observed to only occur above 53 kV, with x-ray burst energies scaling quadratically with voltage. The average delay between the current pulse and x-ray emission was found to be 3.5 ± 0.5 ns, indicating that runaway electrons are produced during the streamer inception phase or no later than the transition stage, when the inception cloud is breaking into streamer filaments. During this short time span, runaway electrons can traverse the gap, hit the ground plate and produce bremsstrahlung x-ray photons. However, streamers themselves cannot traverse more than 3.5 mm across the gap, which supports the idea that runaway electron production is not associated to streamer connection to the ground electrode.