The dense plasma focus (DPF) can be an intense source of x rays, wherein the insulator sleeve strongly dictates the electrical breakdown, which subsequently affects the formation of a plasma sheath and a collapse phase. Experiments on a 25 kJ DPF (operated at 4.4 kJ) are carried out to demonstrate the influence of insulator surface morphology on the pinch structure, dynamics, and x-ray yield using a Ne fill. Two borosilicate insulators are directly compared, one with a smooth finish and the other machined with four circumferential grooves traversing the perimeter of the exterior insulator surface. Comparisons are made through same-shot imaging diagnostics of the evolving plasma sheath during breakdown, rundown, and at the pinch in addition to the time-resolved measurements of emitted x rays via filtered photodiodes. The presence of structures on the insulator sleeve reduces x-ray production across all fill pressures by a factor of 2.8 ± 2.4 on average and reduces the highest x ray producing shots by a factor of 5.5 ± 1.8. Observations of sheath asymmetry and inhomogeneity at lift-off are observed and correlated with subsequent observations of off-axis radial collapse. Taken together, this suggests that local variations in the insulator surface decrease the spatial uniformity of the sheath, leading to an azimuthally asymmetric focus, reduced electron densities, and, ultimately, degraded x-ray production.

中文翻译：

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绝缘体表面处理对填充 Ne 的致密等离子体焦点的夹点动力学和 X 射线产生的影响

密集等离子体焦点 (DPF) 可以是强 x 射线源，其中绝缘套管强烈决定电击穿，这随后会影响等离子体鞘的形成和坍塌阶段。对 25 kJ DPF（在 4.4 kJ 下运行）进行了实验，以证明绝缘体表面形态对使用 Ne 填充的箍缩结构、动力学和 X 射线产率的影响。直接比较了两种硼硅酸盐绝缘子，一种具有光滑的表面，另一种加工有四个环绕绝缘子外表面周边的圆周凹槽。除了通过过滤光电二极管对发射的 X 射线进行时间分辨测量外，还通过在击穿、耗尽和夹点期间对不断演变的等离子体鞘的同拍成像诊断进行比较。绝缘套管上结构的存在将所有填充压力下的 X 射线产生平均减少了 2.8 ± 2.4 倍，并将产生最高 X 射线的镜头减少了 5.5 ± 1.8 倍。观察到的鞘层不对称和不均匀性在抬离时被观察到，并与随后的离轴径向塌陷的观察结果相关联。综上所述，这表明绝缘体表面的局部变化会降低护套的空间均匀性，导致方位角不对称焦点、电子密度降低，并最终降低 X 射线产生。观察到的鞘层不对称和不均匀性在抬离时被观察到，并与随后的离轴径向塌陷的观察结果相关联。综上所述，这表明绝缘体表面的局部变化会降低护套的空间均匀性，导致方位角不对称焦点、电子密度降低，并最终降低 X 射线产生。观察到的鞘层不对称和不均匀性在抬离时被观察到，并与随后的离轴径向塌陷的观察结果相关联。综上所述，这表明绝缘体表面的局部变化会降低护套的空间均匀性，导致方位角不对称焦点、电子密度降低，并最终降低 X 射线产生。