OBSERVATIONS OF 2-DIMENSIONAL MAGNETIC-FIELD EVOLUTION IN A PLASMA OPENING SWITCH

The time dependent magnetic field distribution was studied in a coaxia l 100-ns positive-polarity Plasma Opening Switch (POS) by observing th e Zeeman effect in ionic line emission. Measurements local in three di mensions are obtained by doping the plasma using laser evaporation tec hniques. Fast magnetic field penetration with a relatively sharp magne tic field front (less than or equal to 1 cm) is observed at the early stages of the pulse (t less than or similar to 25). Later in the pulse , the magnetic field is observed at the load-side edge of the plasma, leaving ''islands'' of low magnetic field at the plasma center that la st for about 10 ns. The two-dimensional (2-D) structure of the magneti c field in the r,z plane is compared to the results of an analytical m odel based on electron-magneto-hydrodynamics, that utilizes the measur ed 2-D plasma density distribution and assumes fast magnetic field pen etration along both POS electrodes. The model results provide quantita tive explanation for the magnetic field evolution observed. (C) 1998 A merican Institute of Physics.