Observations of magnetic and electric fields in a nanosecond plasma opening switch experiment

Summary form only given. Magnetic and electric fields are measured in a 140kA, 100ns, positive-polarity plasma opening switch (POS) experiment, using spectroscopic methods. The magnetic field distribution is obtained from Zeeman splitting of ball emission line. Measurements local in r, z and /spl theta/ are obtained using laser evaporation of barium deposited on the inner electrode. The line profiles in two orthogonal polarizations, along and perpendicular to the azimuthal magnetic field, are observed simultaneously by two spectrometers. The profiles are treated self-consistently, accounting for Doppler and Zeeman broadening, to yield the spatially and temporally resolved magnetic field. The current channel propagates axially at a velocity of /spl cong/10/sup 8/ cm/sec, i.e., the magnetic field penetrates the entire plasma within 40ns after the beginning of the generator current. The current is found to flow nearly radially over all the plasma, in a channel much broader than the classical skin depth. At later times, a higher current density region is formed at the load-side edge of the plasma. These observations are in agreement with our previous determination of magnetic field distribution, obtained from ion velocity measurements. Collective electric fields are investigated using Stark broadening of H/sub /spl alpha// and H/sub /spl beta// line profiles, integrated over the axial line of sight. The Doppler and thermal Stark width are determined prior to the POS operation.