In research of Z-pinch, the initial establishment of current in load, current density distribution mode and current evolution characteristics in different stages are of great significance to study the development of plasma dynamics，analyze plasma instability mode and carry out MHD numerical simulation. Thin planar foil is an ideal configuration with continuous two-dimensional structure to study the problem. Based on an ideal model that consist of foil-backpost configuration with assumed infinite length in reverse exploding condition, the establishment, distribution and evolution of the current channel, magnetic field distribution characteristics and the force state of foil plasma by the inductive mode are calculated and analyzed in theory. Relevant experiments were carried on the QG-1 facility with about 1.4 MA peak current and 100 ns rise time to verify. The self-emission graphs of exploding foils were recorded by visible-light frame camera from side-on and end-on views. Different load configuration were utilized including symmetric and asymmetric condition both assembled with two 20-μm-thick aluminum foils. The results show that the establishment of the initial current in foil (0~70 ns) accord with the expectation of the inductance model. The inductance feature determines the distribution of the current in this stage, which cause current aggregation in foil edges and then edges will suffer greatly higher magnetic field and J∧B force than center. This results in a clamp plasma morphology formed. The later images (70~120 ns) show that the intense emission region will transfer from the foil edges to the center which prove a transfer of current channel. So the magnetic field and J∧B force at foil center get increased and a peak convex plasma morphology form then. It shows that the current distribution will be affected by the plasma evolution process. The convergence process of ablated plasma with current finally leads to the rapid switching (60~80 ns) of current channel.
下载:
