The time-dependent electron density and magnetic field distributions in a 70-ns plasma opening switch

The time-dependent two-dimensional electron density distribution is determined for the first time during the operation of a short-conduction plasma opening switch. The electron density, resolved in 3-D, is determined from the line intensities of different ions doped into the plasma. A rise in the electron density followed by a drop is observed to propagate from the generator towards the load at the proton Alfven velocity. Based on spectroscopic magnetic field and ion velocity measurements, the density evolution can be explained as pushing of the protons ahead of the propagating magnetic piston, followed by magnetic field penetration into the rest of the plasma composed of the lower-density heavier ions