In this work, new evidence and information about both the origin and evolution of filamentary structures observed in the current sheath of a small plasma focus (PF) discharge are reported. The experiments were carried out in a small generator of low energy (multipurpose generator) at the PF configuration, under different operating conditions. These include different anode and insulator geometries, without return bars and in a high-performance regime of the generator at high pressures (10 mbar). The evolution of the plasma structures is characterized by means of refractive optical techniques. The electrical behavior of the discharge, as well as its performance, are monitored with conventional electrical diagnostics and neutron and x-ray detectors, respectively. Plasma filaments of the same species are present in all tested configurations, however, in experiments with larger effective anode length (and smaller anode radii), the plasma region containing the filaments moves away from the anode surface and remains confined in a region of the plasma sheath, such as a toroidal plasma belt, without reaching the top of the anode nor participating in the radial compression phase. According to images of the plasma sheath in its early phase, the filaments originate and evolve from a precursor annular plasma formed in the lower part of the anode next to the insulator, during the process of electrical breakdown. The local character that these dense-filamentary structures acquire in the evolution of the plasma sheath would discard the current-filament hypothesis. On the other hand, experiments performed in deuterium gas with anodes of larger effective lengths and without filaments in the radial compression phase allowed the production of neutrons and x-rays at a high performance.
本工作中，报告了在小型等离子体聚焦（PF）放电装置中观察到的丝状结构的新证据及其起源与演化的相关信息。实验是在一台低能量（多功能）小型发生器上，以PF构型在不同工作条件下进行的。这些条件包括不同的阳极和绝缘体几何形状、无回流杆，以及在高气压（10 mbar）下的高性能运行模式。等离子体结构的演化通过折射光学技术进行表征。放电的电学行为及其性能分别通过常规电诊断以及中子探测器和X射线探测器进行监测。在所有测试构型中均存在相同类型的等离子体丝状结构，然而，在有效阳极长度较大（且阳极半径较小）的实验中，包含丝状结构的等离子体区域会远离阳极表面，并被约束在等离子体鞘层内的一个区域中，例如环形等离子体带，而不会到达阳极顶端，也不会参与径向压缩阶段。根据等离子体鞘层早期的图像，这些丝状结构起源于击穿过程中在阳极附近、绝缘体旁形成的环形初始等离子体，并从中演化而来。这些致密丝状结构在等离子体鞘层演化过程中所获得的局部特性，否定了电流丝假说。另一方面，在氘气中采用有效长度较大且无丝状结构的阳极进行的实验，在径向压缩阶段未出现丝状结构，却实现了高性能的中子和X射线产生。