Spatially and temporally resolved spectroscopic measurements of the magnetic field, electron density, and turbulent electric fields are used to study the interaction between a pulsed magnetic field and a plasma. In the configuration studied (known as a plasma opening switch) a 150 kA current of 400 ns-duration is conducted through a plasma that fills the region between two planar electrodes. The time-dependent magnetic field, determined from Zeeman splitting, is mapped in three dimensions, showing that the magnetic field propagation is faster than expected from diffusion based on the Spitzer resistivity. Moreover, the measured magnetic field profile and the amplitude of turbulent electric fields indicate that the fast penetration of the magnetic field cannot be explained by an anomalously high resistivity. On the other hand, the magnetic field is found to penetrate into the plasma at a velocity that is independent of the current-generator polarity, contradictory to the predictions of the Hall-field theory...

https://plasma-gate.weizmann.ac.il/Pubs/pop2003_10_112.pdf

Observation of faster-than-diffusion magnetic field penetration into a plasma

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.

/pdf/observations-of-two-dimensional-magnetic-field-evolution-in-5d7z0efy9z.pdf

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

Spectroscopic investigations of the properties of a plasma produced by a flashboard plasma source, commonly used in pulsed plasma experiments, are presented. The plasma is used to prefill a planar 0.4 μs conduction time plasma opening switch (POS). A novel gas-doping technique and a secondary surface flashover plasma source are used to locally dope the plasma with gaseous and solid materials, respectively, allowing for spatially resolved measurements. The electron density, temperature, and plasma composition are determined from spectral line intensities and line profiles. Detailed collisional-radiative modeling is used to analyze the observed line intensities. The propagation velocity and divergence angle of various ions are determined from time-of-flight measurements and Doppler broadening of spectral lines, respectively. This allows for distinguishing the secondary plasma ejected from the POS electrodes from the plasma of the flashboard source.

https://plasma-gate.weizmann.ac.il/Pubs/pop3797.pdf

Spectroscopic investigations of a dielectric-surface-discharge plasma source

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 motion showed magnetic field penetration through the 3.5 cm long plasma at a velocity ≂108 cm/s. The current density was found to be relatively high at the load‐side edge of the switch plasma. It is suggested that this may cause plasma acceleration into the vacuum section toward the load, which is supported by charge‐collector measurements. The fast magnetic field penetration agrees with estimates based on the Hall‐field mechanism.

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

The interaction between a moving magnetic-field front and a low-collisionality plasma consisting of different ion species is investigated using spatially and temporally resolved spectroscopic techniques. The experiment is carried out in a plasma-opening-switch configuration, in which a current rising to 150 kA in 400 ns is conducted through a plasma that prefills the region between two planar electrodes. Ion-species separation is found to occur, similarly to the results reported for a 80 ns duration plasma-opening-switch experiment of cylindrical geometry, which was not necessarily expected since in the present experiment plasma pushing is more substantial. The separation, in which the light-ion plasma (protons) is reflected while the heavy-ion plasma (carbon) is penetrated by the propagating magnetic-field, is investigated by determining the electron density from the temporal evolution of spectral lines, the nonprotonic ion velocities from line-emission Doppler shifts, and the proton velocity distributio...

/pdf/investigation-of-the-ion-dynamics-in-a-multispecies-plasma-258b9r72y5.pdf

Investigation of the ion dynamics in a multispecies plasma under pulsed magnetic fields

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...

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

In this Letter we present a simple and reliable method for the determination of the mean amplitude of the nonthermal fields and the ion Doppler temperature, based on the analysis of the Stark and Doppler broadening autocorrelation function. The method makes no assumption on the distribution function of the turbulent field or that the nonthermal fields are quasistatic. An independent ``typical field'' analysis may be performed to obtain information on the field frequency.

Novel spectroscopic method for analysis of nonthermal electric fields in plasmas.

s 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);

/pdf/spectroscopic-investigations-of-the-plasma-behavior-in-a-524bsirera.pdf

Spectroscopic Investigations Of The Plasma Behavior In A 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.

http://ieeexplore.ieee.org/iel3/3932/11381/00531616.pdf

S. Alexiou

Papers

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

Novel spectroscopic method for analysis of nonthermal electric fields in plasmas.

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

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