Abstract: When the shock front (SF) hits the central electrode
axis of plasma focus device, a reflected shock wave moves radially
outwards. The current sheath (CS) results from ionization of filled
gas between two electrodes continues to compress inwards until it
hits the out-going reflected shock front. In this paper the Lagrangian
equations are solved for a parabolic shock trajectory yielding a first
and second approximation for the CS path. To determine the
accuracy of the approximation, the same problem is solved for a
straight shock.