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[References: 16 tit.]

This paper presents the results of measuring the expansion velocity of the plasma generated by an electrical breakdown occurring along an exploding aluminum foil. The test foils were 6 μm thick and 20 mm long; their width was varied in the range of 0.93 to 1.05 mm. The foil explosion was initiated by a sinusoidal current of period 1780 ns. The current amplitude was varied by varying the charge voltage of a 0.25-μF capacitor (10, 20, and 30 kV), and it was about 6.5, 14, and 22 kA, respectively. The plasma velocity measurements were performed using two grounded probes located at different distances from the edges and the center of the exploding foil (from 2 to 16 mm). The time interval was measured between the occurrence of a probe signal and the initiation of breakdown along the foil. The plasma expansion velocity was estimated from the measured time of flight of the plasma from the foil to a probe. Besides the probe measurements, optical images of the exploding foil and of the expanding luminous plasma were recorded using an HFSC Pro framing camera with an exposure time of 3 ns. These investigations made it possible to visualize the shape of the forming plasma sheath and to measure the expansion velocity of the bulk of the desorbed gases and metal vapor as a function of time. In addition, they gave ideas of the processes occurring in the near-electrode regions at the time of breakdown initiation.