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A variety of schemes have been proposed over the last two decades for delivering lethal amounts of energy and/or momentum to targets such as missiles and high speed aircraft. Techniques have ranged from high energy lasers and high voltage charged-particle accelerators to less exotic but still challenging devices such as electromagnetic railguns. One class of technology involves the use of high speed plasmas. The primary attraction of such technology is the possibility of utilizing relatively compact accelerators and electrical power systems that could allow highly mobile and agile operation from rocket or aircraft platforms, or in special ordnance. Three years ago, R & D Associates examined the possibility of plasma propagation for military applications and concluded that the only viable approach consisted of long dense plasma jets, contained in radial equilibrium by the atmosphere, while propagating at speeds of about 10 km/s. Without atmospheric confinement the plasma density would diminish too rapidly for adequate range and lethality. Propagation of atmospherically-confined jets at speeds much greater than 10 km/s required significant increases in power levels and/or operating altitudes to achieve useful ranges. The present research effort has been developing the experimental conditions necessary to achieve reasonable comparison with theoretical predictions for plasma jet propagation in the atmosphere. Time-resolved measurements have been made of high speed argon plasma jets penetrating a helium background (simulating xenon jets propagating into air). Basic radial confinement of the jet has been observed by photography and spectroscopy and structures in the flow field resemble those predicted by numerical calculations. Results from our successful initial experiments have been used to design improved diagnostic procedures and arcjet source characteristics for further experiments. In experiments with a modified arcjet source, radial confinement of the jet is again observed, with the 3 cm exit diameter of the jet preserved downstream for the duration of the quasi-steady flow. The modification of the arcjet consisted of the addition of a converging-diverging nozzle upstream of the 3 cm diam exit of the arcjet to expand the jet further before its entry into the background atmosphere. The jet penetrates for tens of diameters into the target atmosphere at a speed of 2 km/s, with an estimated jet flow speed of 5.3 km/s. The jet diameter is maintained for the range of the jet, which appears to equal 1 to 1.5 times the product of jet penetration speed and pulse duration (- 350 As in the present experiments), as expected from theoretical considerations. Further modification of the arcjet source (increasing throat diameter and electrode radius ratio) and extension of the current pulse time are expected to increase the jet range.
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