丝阵负载Z箍缩早期过程的研究

Research on early stages of wire array Z-pinch

利用X箍缩等离子体产生的μm级、亚ns脉冲X射线点源对双丝电爆炸过程进行了X射线背光照相,结果表明:真空环境下爆炸丝通常形成"核冕"结构,即高密度丝核表面围绕着低密度冕等离子体;随后在全局磁场驱动下,冕层将被连续剥离并向轴线汇聚,形成"先驱等离子体",大大降低丝阵的内爆品质。针对上述问题,进一步对实现"无核丝爆"(提高丝核沉积能量实现金属丝的均匀汽化)的方法进行了研究。实验结果表明:提高驱动电流上升率以及在金属丝表面构造正向径向电场均有利于丝核沉积能量的提高。结合上述两种方法,提出了阴极串联闪络开关的电极构型,大幅度提高了丝核沉积能量:正负极性驱动电流下比能量分别提高到原来的2倍(从5.7eV/atom到13eV/atom)和3.5倍(3.4eV/atom到12eV/atom),均超过了钨丝汽化能(8.8eV/atom),且激光干涉图像表明爆炸产物具有很高的汽化率,即实现了"无核丝爆"。

Electrical explosion of wire (EEW) is the first stage of wire array Z-pinch, which has great influence on the following dynamics and the final X-ray emission. In this paper, the physical processes of two-wire Z-pinch was observed by X-ray backlighting. The sub-nanosecond? micrometer-scale X-ray source was generated with X-pinches connected in series with the Z-pinch. Experimental results show that electrically exploded wires in vacuum usually develop into “core-corona” structure (high-density core surrounded by low-density corona plasma). The corona plasma is then driven to the axis by global magnetic field to form a precursor plasma column, adding to the instabilities of the implosion stage. Therefore single wire EEW experiments were carried out to increase the energy deposition of wire core so as to suppress the formation of <<core-corona>, structure. Experimental results show that the performance of EEW can be improved by higher rising-rate of driving current and positive radial electric field along wire surface. In order to combine the two favorable methods9 a flashover switch was inserted between wire-end and cathode. As a result, the specific energy of EEW was increased by 2 times (5. 7 eV/atom vs 13 eV/atom) and 3. 5 times (3. 4 eV/at-om vs 12 eV/atom) under positive and negative driving current , exceeding the atomization enthalpy of tungsten (8. 8 eV/atom) by a factor of 1.4. The laser interferogrcims show no high-density wire core; in other words? Fully vaporized (core-free) wire explosion of bare tungsten wire was achieved.