CURRENT DISTRIBUTION AND FLOW MODEL FOR LARGE RADIUS-RATIO MAST
AVCO EVERETT RESEARCH LAB INC EVERETT MA
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The non-uniform flow in a magnetic annular shock tube MAST with an annular spacing larger than the radius of the inner cylinder is described. Experiments were conducted in a MAST with inner and outer ra ii of 1 and 3 inches. The speed of the disturbance produced in the tube was found to depend upon the polarity of the discharge. The distribution of current in the tube was determined with probe coils it too, depended on polarity. With the inner electrode positive the current was largely confined to a thin sheet that was strongly canted with respect to the walls, the inner edge leading. A thicker current sheet that was nearly normal to the tube walls was observed in the inverse polarity condition. A model is proposed to explain the operation with positive center electrode. The shape of the forward part of the current sheet is calculated by balancing the magnetic pressure behind the sheet with the gas pressure in front the Newtonian approximation is used for the gas pressure. The resulting shape, which is approximately parabolic, agrees roughly with experiment. It is proposed that the dependence of the flow on polarity is associated with electron emission problems, and that in positive operation the ions carry a substantial part of the current.
- Electricity and Magnetism