Figure 2. Distance travelled by shock front, : 20mm spark gap, discharge energy 113 J, energy per unit length 5.7x10³ J m^-1 : 4mm spark gap, discharge energy 42 J, energy per unit length 1.1x10⁴ J m^-1, 500 mbar pressure.

Also shown for comparison is the radial propagation of the shock front as calculated by Hill [1971] (-------- 1013 mbar pressure, 1.4x10⁴ J m^-1) and Lin [1954] (-- -- -- = 1.4, 500 mbar, 5.7x10³ J m^-1).