Hypervelocity Plasma Sprayer Using Railgun Accelerators
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This paper describes hypervelocity plasma spraying with railgun systems and describes the laboratory system designed and built at The University of Texas at Austin, which successfully validated the method of hypervelocity plasma spraying and conducted proof of principle experiments for hypervelocity plasma-powder deposition, using a railgun system. The bore of the railgun is filled with an ionizable gas, and a radio frequency-excited cavity provides a line source of plasma. Fast, high-energy electrical pulses from the magnetic flux compression device expand the plasma line into a planar arc driven by Lorentz forces. The arc is an efficient >snowplow> sweeping the gas to velocities of 4 to 5 km/s, which is twice the desired powder velocity producing coatings of superior quality in an almost continuous manner, compared to the existing plasma sprayers as shown by state-of-the-art Hadland CCD framing cameras. The paper mentions how the Rayleigh Taylor instabilities are circumvented and the role and the interplay of the compensated current pulse shape of pulsed machines. For a technology to be viable, the process must be driven on a continuous basis. Then the power source must be also an energy storage device capable of a large number of shots, repeated at a relatively high frequency. The process requires an average power of 250 kW, but in successive pulses of 100 ms duration at a peak power level of 80,000 kW. In order to operate without interruption, novel concepts of repetitive pulsed electrical machines were developed. One refers to an actively compensated compulsator - embedding a capacitive pulse forming network. The second is a pair of series-excited de generators operating in tandem.