Air Force Research Laboratory

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Shiva Star Fast Capacitor Bank

The High Power Systems Branch performs exploratory experimental and computational research on military applications of high-energy pulsed power systems. Pulsed power consists of generating very high voltages and very high currents in very short periods of time. Voltages range from thousands to millions of volts, currents range from thousands to millions of amps, and pulse widths range from billionths (nanoseconds) to millionths (microseconds) of a second. Pulsed power systems are described by the amount of energy they store in joules or the power they deliver in watts. Typical pulsed power systems will store millions of joules (megajoule) and deliver billion-billion watts (terawatts) of power. A typical car battery stores about 3 megajoules of energy but can only discharge it over minutes to hours. A terawatt is equivalent to the power generated by 800 Hoover Dams but pulsed power generates this kind of power for only several billionths to millionths of a second.

Shiva Star is the Air Forceís largest pulsed power system. Shiva Star will store nearly 10 million joules of energy (equal to 5 pounds of TNT). It produces a pulse of 120 thousand volts and 10 million amps for down to one millionth of a second to produce a power flow equivalent to a terawatt. Shiva Star has evolved from a 1 megajoule system in 1975, a 2 megajoule system in 1979, to its final form as a 10 megajoule system in 1982. Shiva Star has been used over the years for many different types of experiments such as pulse compression to increase energy in the pulse, plasma liner implosion for production of x-rays, solid liner implosions to compress matter to high density and pressure, compact toroids for generating high energy plasmas, and simulation of explosive pulsed power generators.

Pulsed power has been used since the 1950ís for simulation of nuclear weapons effects. Nuclear weapons produce high levels of x-rays, which disrupt or destroy sensitive electronic equipment. Satellites are very susceptible to x-rays since the atmosphere normally absorbs x-rays. To produce a high level of x-rays similar to a nuclear weapon, an electron beam is generated by a pulsed power system and aimed at a heavy metal target, such as tantalum. As the electrons are slowed down or stopped by the heavy metal, x-rays are produced. This techniques produces a short burst of high energy x-rays similar, though at a much lower intensity, to those produced by the detonation of a nuclear device. Shiva has been used to develop the technology to go into simulators to increase the amount of x-rays produced and to improve the quality of those x-rays to better simulate a nuclear weapon.

Present work on Shiva Star is implosion of spherical liners. Very high currents pass through a nearly spherical shell, which causes it to collapse to a very small dense region. Pressures on the order of 10 million times atmospheric pressure have been generated. This high-density region can be used to study interactions between protons and anti-protons. In the coming years, anti-protons will be injected into the high-density region in order to measure the energy generated when the protons and anti-protons combine. Other work on Shiva Star involves simulating explosive pulsed power generators. By using Shiva Star, various aspects of explosive pulsed power can be studied and improvements made much quicker than using actual explosives. Explosive pulsed power is used in one-shot operations to generate a very high current pulse in a very compact package.

To support the research performed to date, Branch personnel have become experts in diagnosing high-energy pulsed power systems by using magnetic probe arrays, laser interferometry, time- and space-resolved optical spectroscopy, x-ray grazing incidence, photodiode array spectroscopy, x-ray pinhole photography, and fast optical photography.

In addition to the vigorous experimental research being performed, the Branch works closely with the Theoretical and Computational Branch. This group utilizes radiation magnetohydrodynamic (MHD) computer codes, particle-in-cell (PIC) simulations, and various analytic tools to study high-energy plasma physics.

The main computational workhorse for the computational branch is the 2-1/2 dimensional radiation MHD code, MACH2. MACH2 is an Arbitrary Lagrangian-Eulerian, non-ideal MHD code with non-equilibrium radiation diffusion that allows for problems with complex geometric shapes. It runs on desktop workstations and supercomputers. MACH2 is routinely used to simulate Shiva Star experiments and has been used to design various stages of experiments. In addition, MACH2 is used to simulate advanced concepts that might not be built for several years.

Air Force Research Laboratory
Directed Energy Directorate
Current as of May 1998