NANOSECOND PLASMA-FLOW-SWITCH AS THE OUTPUT DEVICE ON THE S-300 PULSED POWER GENERATOR ∗ A. Kingsep ξ , Yu. Bakshaev, A. Bartov, P. Blinov, A. Chernenko, R. Chikin, K. Chukbar, S. Danko, L. Dubas, Yu. Kalinin, I. Kovalenko + , A. Lobanov + , V. Mizhiritsky, V. Shchagin, V. Smirnov RRC “Kurchatov Institute”, 1 Kurchatov Sq., Moscow, 123182, Russia + Moscow Institute for Physics and Technology, Dolgoprudnyi, 141700, Russia ∗ Work supported by the Russian Department of Atomic Energy and partially by the Russian Foundation for Basic Research, grant 01-02-17359, and by the Russian grant “Scientific School” NSH-2292.2003.2 ξ email: kingsep@dap.kiae.ru Abstract On the S-300 pulsed power generator (4.5 MA, 70 ns, 0.15 Ohm), within the frames of ICF program based on fast high-current Z-pinches, experiments are being carried out studying promising schemes of output units. In particular, a device similar to the plasma flow switch is being investigated aimed at sharpening the pulse. In the experiments with such a device, by means of variation the geometry of the inner electrode of a co-axial, as well as the acceleration of a cascade of plasma “washers”, the switching of the current up to 750 kA has been obtained, with the rise time ~ 5–7 ns and subsequent decrease being in accordance with that of the net current (~ 100 ns). Thereby the opportunity of switching of much more amount of energy onto the load has been demonstrated compared to our preliminary experiments (2.5 MA/2.5 ns). Soft X-ray radiation from the cavity was recorded by means of vacuum diodes with a nickel cathode and especially selected filters. The radiative temperature of the cavity walls estimated from the ratio of diode signals was close to 50 eV. I. INTRODUCTION Fast compression of high-current Z-pinches is under consideration as a possible approach to electric energy conversion into X-ray pulse at the energy scale of dozens of megajoules aimed at the inertial confinement fusion (ICF) as well as experimental study of the extreme state of matter. Nowadays, the typical load of the pulsed power machine of megaampere range is based on the array of wires of the micrometer thickness. Scientific cooperation including TRINITI, Kurchatov institute, Efremov institute, and VNIITF develops the “Baikal” project [1,2] in which an inductive storage has to be used which in the case of successive transformation procedure could produce an electric pulse with parameters adequate for ICF. Unfortunately, one of the shortcomings of such schemes is the X-ray radiation into the solid angle equal to 4π that results in the reduction of energy density and, consequently, the equivalent temperature since the radiation fills the whole volume of the output unit. As a result, the experiments with a Hohlraum are available now only on the level of “Z”-machine at “Sandia” laboratories [3]. The goal of ICF experiments in Kurchatov institute is to study some new kinds of tiny output units those could provide the Hohlraum experiments at the current generation of high-current machines. II. NANOSECOND PLASMA FLOW SWITCH We investigated especial output devices similar to the plasma flow switch but operating in the nanosecond range of pulse duration. The plasma bridge between the inner and outer cylinders was accelerated along the axis by means of the current pulse of generator. The scheme of our output device has been shown in Fig. 1. Accelerated plasma bridge moves along the inner coaxial cylinder. When it is flying through the break of the inner cylinder, the circuit becomes to be broken, as a result, the magnetic flux enters the central cavity where the load is situated. The plasma bridge was created by means of the current-driven explosion of a thin foil in very beginning of the current pulse. Diameters of inner and outer cylinders were equal to 4 and 10 mm, respectively. The break of inner cylinder was varied between 1 to 2.6 mm. The diameter and length of central cavity were equal to 3.6 mm and 10 mm, respectively. The maximal current value was close to 2.5 – 3.0 MA. We used the accelerated foils produced of different materials, to wit, metallic foils as thick as 5 – 10 µm, mylar films of 2 – 5 µm, nitro- cellulose films with thickness < 1 µm, and aluminum- coated mylar films of 1.2 – 1.5 µm. The homogeneity of breakdown of foils and the velocity of their sliding along the inner electrode were recorded by means of both frame 0-7803-7915-2/03/$17.00 ©2003IEEE. 689