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UBC Theses and Dissertations

Electrical power extraction from a supersonic plasma flow Kwan, Wai-Ming Joe


The induced potential difference across a standing shock front can be used to drive electric current through external loads. Such a "standing shock generator" presents an alternative scheme to the MHD generator for direct conversion of energy from high temperature supersonic flows. We make use of the supersonic flow behind a free running shock in a shock tube and let the flow impinge onto a conical obstacle mounted in the middle of the tube to create a standing shock. This cone has a conducting surface which acts as the anode. The cathode is mounted flush with the shock tube wall at a position upstream of the standing shock. By varying the load resistance, we have obtained current-voltage characteristics for the standing shock generator. These characteristics are families of parallel straight lines similar to the characteristics of a battery. The open-circuit voltage is found to depend on the standing shock potential and the work functions of the electrodes. The internal resistance (equivalent to the slope of the characteristic) is found to be dominated by the plasma-wall interaction at the surface boundary layers. The maximum current collected by the electrode is therefore limited to its ion saturation current. A typical result of the standing shock generator in our experiment gives 1 volt with 0.5.amp for the. 30X10⁻⁶ sec test time duration.

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