Spectroscopic investigations of the plasma behavior in a plasma opening switch experiment

Abstract

The electron density, the electron kinetic energy, the particle motion, and electric fields in a coaxial positive-polarity plasma opening switch (POS) were studied using spectroscopic diagnostics. A gaseous source that injects the plasma radially outward from inside the inner POS electrode was developed. The plasma was locally seeded with various species, desired for the various measurements allowing for axial, radial, and azimuthal resolutions both prior to and during the 180 ns long current pulse. The electron density was determined from particle ionization times and the electron energy from line intensities and time dependent collisional-radiative calculations. Fluctuating electric fields were studied from Stark broadening. The ion velocity distributions were obtained from emission-line Doppler broadenings and shifts. The early ion motion, the relatively low ion velocities and the nearly linear velocity dependence on the ion charge-to-mass ratio, leads to the conclusion that the magnetic field penetrates the plasma early in the pulse. The ion velocity dependence on the axial location were thus used to infer the time dependent axial distribution of the magnetic field, indicating the formation of a relatively high current density at the load-side edge of the plasma. This is expected to cause plasma acceleration towards the load, found to be supported by charge-collector measurements. The fast magnetic field penetration could be explained by mechanisms based on the Hall effect.

Plasma dynamics in pulsed strong magnetic fields

“…advance this basic study, nonintrusive spectroscopic diagnostic methods were developed and employed to determine the key plasma parameters. Spectroscopy combined with novel plasma doping techniques allowed for time-dependent, threedimensional ͑3D͒ spatially resolved measurements of the plasma composition, 17,18 magnetic field evolution, [19][20][21] ion dynamics, [22][23][24] electron energy distribution, and nonthermal electric fields. 21,22,25,26 In particular, the use of Zeeman splitting of emission lines from the plasma constituents is highly advantageous, since it yields unambiguously the magnetic field inside the plasma.…”

Novel gas-doping technique for local spectroscopic measurements in pulsed-power systems

“…These line intensities are seen to drop as a result of ionization, and the ionization times thus obtained, together with the knowledge of the electron density and the use of collisionalradiative calculations, 16 allowed for the determination of the electron temperature, found to be 8-10 eV. This technique can also be used to study electron flow and proton plasmas between the POS and the load, 17,10 which is important for the understanding of the energy coupling to the load.…”

“…To this end, we developed various doping techniques such as doping dielectric electrodes undergoing flashover 9 and laser evaporation of coated electrodes. 10 Here, we report on the development of molecular beam injection, previously used in chemistry studies, 11 to locally dope the plasma in a POS experiment with various species used to select emission lines for different spectroscopic observations. Unlike the previously reported method based on laser evaporation, 10 the present method allows for the injection of gaseous atoms for which the ionization times are sufficiently long to extend the measurement of line intensities and spectral profiles to a longer period during the switch operation.…”

“…10 Here, we report on the development of molecular beam injection, previously used in chemistry studies, 11 to locally dope the plasma in a POS experiment with various species used to select emission lines for different spectroscopic observations. Unlike the previously reported method based on laser evaporation, 10 the present method allows for the injection of gaseous atoms for which the ionization times are sufficiently long to extend the measurement of line intensities and spectral profiles to a longer period during the switch operation. Evidently, line emission from ions produced due to the ionization of the injected atoms can also be used for various measurements, as is shown below.…”

Diagnostics and Investigations of the Plasma and Field Properties in Pulsed-Plasma Configurations

“…These methods can be applicable to a wide variety of devices, including electron diodes (1) , ion diodes (2) , high power magnetrons (3) , plasma opening switches (4) , and various plasma implosion devices such as Z-pinches (5) . Techniques recently developed allow for determining the electric field distribution from Stark shift (6) (7) and broadening (8) (10) , the magnetic field distribution from Zeeman splitting (11) (15) , the ion velocity distribution from Doppler broadenings and shifts (16) (18) , the electron temperature from line-intensity ratios (19) , the electron density from the particle ionization times (17) (18) , and the particle density distributions from the absolute intensities of various spectral lines (20) . Laser spectroscopy allows for particularly high-spatial-resolution measure-ments of ion velocities, electron density and temperature, and electric fields (21) .…”