Magnetic opening switch shaping the pressure pulse for high-speed liner implosion by high-current explosive generator

摘要

The paper presents the results of the experiment in which the liner implosion was realized by a pressure pulse shaped by a magnetic opening switch. The current of the high-current explosive generator flows through the ring element of the magnetic opening switch during the time of 430 /spl mu/s till it rises to 10 MA. The diameter of the copper ring element was 100 mm, length along the axis was 15 mm, and its thickness was 1.2 mm. The ring element was connected to the current-conducting electrodes by the bridges only 0.2 mm thick. Under the effect of magnetic pressure from the flowing ultra-high current the ring element expands in the radial direction. A thin bridge 0.2 mm thick is easily cut in the beginning of the element expansion, and then the ring element is only in sliding contact with the electrodes. Having run the distance of 14 mm, the ring element slides off the current-conducting electrodes. Separation of the ring element happened 30 /spl mu/s prior to the explosive high-current generator operation completion and prior to reaching the maximum current in it. At the moment of separation the rate of the ring element radial expansion was 1.5 mm//spl mu/s. A volumetric arc appears in the gap between the ring element and the current- conducting electrodes. Under the effect of magnetic pressure of /spl sim/ 10/sup 9/ Pa the magnetized plasma spreads into a toroidal cavity of the coaxial above the imploding cylindrical liner. The peak current in the high-current explosive generator was 19 MA. The amplitude of current in the toroidal cavity of the coaxial above the imploding liner generated after the separation of the opening magnetic switch ring element from the electrodes was 18 MA, the time of current rise from 4 MA to 18 MA in the coaxial above the liner was 8 /spl mu/s. The aluminum liner initial diameter was 100 mm, the wall thickness was 1 mm. The radial rate of the liner implosion was 6.2 km/s. The analysis demonstrates that the liner acceleration was provided by a combined action of gaskinetic and magnetic pressure of magnetized plasma. The advantage of the magnetic opening switch is its design simplicity, and also the fact that the pressure pulse shaping is not accompanied by the high-current generator current interruption but is realized by a continuous travel of the conducting medium towards the liner. This increases the efficiency of energy usage for liner implosion. The disadvantage is that as the liner radius decreases the pressure in it increases less than in case of direct current transfer to the liner. In the experiment considered the toroidal cavity of the coaxial above the liner was not vacuumized. The liner implosion rate may be higher in case the cavity is vacuumized and in case the ring element slide-off moment in the magnetic opening switch is delayed towards the moment of peak current in the high-current generator.