R. Shpitalnik

Observations of two-dimensional magnetic field evolution in a plasma opening switch

The time dependent magnetic field distribution was studied in a coaxial 100-ns positive-polarity Plasma Opening Switch (POS) by observing the Zeeman effect in ionic line emission. Measurements local in three dimensions are obtained by doping the plasma using laser evaporation techniques. Fast magnetic field penetration with a relatively sharp magnetic field front (⩽1 cm) is observed at the early stages of the pulse (t≲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 last for about 10 ns. The two-dimensional (2-D) structure of the magnetic field in the r,z plane is compared to the results of an analytical model based on electron-magneto-hydrodynamics, that utilizes the measured 2-D plasma density distribution and assumes fast magnetic field penetration along both POS electrodes. The model results provide quantitative explanation for the magnetic field evolution observed.

Spectroscopic investigation of fast (ns) magnetic field penetration in a plasma

The time‐dependent magnetic field spatial distribution in a coaxial positive‐polarity plasma opening switch (POS) carrying a current ≂135 kA during ≂100 ns, was investigated by two methods. In the first, ionic line emission was observed simultaneously for two polarizations to yield the Doppler and Zeeman contributions to the line profiles. In the second method, the axial velocity distribution of ions was determined, giving the magnetic field through the ion equation of motion. This method requires knowledge of the electron density, here obtained from the observed particle ionization times. To this end, a lower bound for the electron kinetic energy was determined using various line intensities and time‐dependent collisional‐radiative calculations. An important necessity for POS studies is the locality of all measurements in r, z, and θ. This was achieved by using laser evaporation to seed the plasma nonperturbingly with the species desired for the various measurements. The Zeeman splitting and the ion moti...

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

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 penetrat...

Visible-light spectroscopy of pulsed-power plasmas (invited)

We describe the investigations of the plasma behavior in three pulsed‐power systems: a magnetically insulated ion diode, and plasma opening switch, and a gas‐puffed Z pinch. Recently developed spectroscopic diagnostic techniques allow for measurements with relatively high spectral, temporal, and spatial resolutions. The particle velocity and density distributions within a few tens of microns from the dielectric‐anode surface are observed using laser spectroscopy. Fluctuating electric fields in the plasma are inferred from anisotropic Stark broadening. For the plasma opening switch experiment, a novel gaseous plasma source was developed which is mounted inside the high‐voltage inner conductor. The properties of this source, together with spectroscopic observations of the electron density and particle velocities of the injected plasma, are described. Emission line intensities during the switch operation are discussed. In the Z‐pinch experiment, spectral emission‐line profiles of various charge‐state ions ar...

Spectroscopic Investigations Of The Plasma Behavior In A Plasma Opening Switch Experiment

Abstracts IEEE hztemational Conference on Plasma Science, Tampa, Florida, 1992 (The Institute of Electrical and Electronics Engineers, New York, 1992), p. 166. 32M. Sarfaty, Ya. E. Krasik, R. Arad, A. Weingarten, S. Shkolnikov, and Y Maron, in Ref. 27, p. 633; A. Weingxten, M.Sc. thesis, Feinberg Graduate School, Weizmann Institute of Science, Israel, 1993. 33M. Sarfaty, R. Arad, Ya. E. Krasik, Y. Maron. B. Peryaslovetz, S. Shkolni- kov, R. Shpitalnik, and A. Weingarten, Bull. Am. Phys. Sot. 38, 1895 (1993). 34Yu. Ralchenko (private communication, 1993). 35H. J. Kunze and H. R. Griem, Phys. Rev. Lett. 21, 1048 (1968). 36G. V. Sholin and E. A. Oks, Sov. Phys. Dokl. 18, 254 (1973). 37H G. Griem, Spectral Line Broadening by Plasmas (Academic, New York 1674). “G Bekefi C. Deutch, and B. Yakobi, in Principles of Laser Plasmas, edited by b. Beketi (Wiley, New York 1976). “E. Sarid. Y. Maron, and L. Troyansky, Phys. Rev. E 48, 1364 (1993). ‘ @H. Tawara, T. Kato, and M. Ohnishi, At. Data Nucl. TabIes 36, 167 (1987);

2D magnetic field evolution and electron energies in plasma opening switches

Summary form only given, as follows. We present measured time dependent 2-D structures of the magnetic field in two plasma opening switches (on 100 ns and 0.5 /spl mu/s time scales), together with an analytical model based on EMHD used to explain the data for the short time switch. The magnetic field, local in 3-D, is obtained by doping the plasma with various species and observing the Zeeman splitting of their spectral lines, using polarization spectroscopy. In the coaxial 100-ns switch, fast (/spl sim/10/sup 8/ cm/s) field penetration with a relatively sharp field front is observed, together with a non-monotonic axial distribution later in the pulse. The model developed, that utilizes the measured 2D plasma density distribution and assumes fast field penetration along both POS electrodes, provides quantitative explanation for the observed field evolution. In the planar 0.5 /spl mu/s switch, a 3-D mapping of the field is obtained. The current channel, 2.5 cm wide, is found to propagate downstream at a velocity /spl sim/3/spl times/10/sup 7/ cm/s. The electron energy in the current channel is studied spectroscopically. The replacement of electrons and the energy dissipation due to the field penetration will be discussed. A comparison of the result for the two time-scale switches and for opposite charging polarities in the coaxial switch will be presented.

Spectroscopic determination of the time dependent magnetic field distribution in pulsed-power plasmas

Summary form only given. Observation of the magnetic field distribution in short-duration plasmas is of major importance since it allows for investigating the field penetration mechanisms and for determining the energy dissipation in the plasma. The current density obtained allows the electron drift velocity to be known, using independent measurement of the electron density. In the case of field diffusion, the penetration depth gives the plasma conductivity yielding the plasma Ohmic heating. Here, we report on the determination of the magnetic field distribution in a coaxial Plasma Opening Switch (POS) and a gas-puffed Z-pinch plasma using two methods: 1) Observation of the Zeeman splitting of emission lines where emissions with two different polarizations were observed in a single discharge in order to discriminate the Zeeman splitting against the inevitable Doppler line broadening of ions moving under the field gradients. 2) Observation of the ion acceleration due to the field gradients from the line Doppler shifts. Together with the electron density determined from particle ionization times and Stark broadening, this yields the magnetic field gradient. For these methods, lines from heavy ions (such as Ba II) and light ions (Li II, C II-C V, Mg II, Ca II), respectively, were used in order to minimize or maximize the Doppler contribution to the line profiles.

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.