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  • 1
    Electronic Resource
    Electronic Resource
    Time-dependent collisional-radiative model for quantitative study of nonequilibrium plasma (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 5016-5027 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this paper fully time-dependent collisional-radiative (CR) calculations are used to study the highly dynamic nonequilibrium anode plasma in a magnetically insulated-diode experiment. The CR model for the C i–C iv atomic system is described in detail, including the radiative and collisional rates and the level structure of the system. The electron temperature is determined by comparing time-dependent line intensities for C ii and C iii ions to calculations of level-population ratios in which continuous particle injection from the anode surface into the plasma is taken into account. The electron temperature is approximately 7 eV. The time-dependent injected fluxes and the fluxes accelerated away from the plasma for C i, C ii, and C iii are determined by inverting the coupled CR rate equations. The calculated extracted flux near the end of the pulse is consistent with the measured carbon-ion current drawn from the plasma. Injection of excited particles is also investigated and is found to be important during the rise of the current pulse (≤50 ns). The importance of including multiple branching for ionization into excited final states is also shown. The time-dependent cooling rate due to inelastic electron-ion collisions and radiative processes is derived for general level-population distributions and is used to investigate the anode plasma. This work should also be relevant in the study of other pulsed-power nonequilibrium plasmas, such as recombining plasmas that have applications for UV and x-ray lasers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347089
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  • 2
    Electronic Resource
    Electronic Resource
    Spectroscopic investigations of a dielectric-surface-discharge plasma source (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 3797-3807 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1286801
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  • 3
    Electronic Resource
    Electronic Resource
    Observations of two-dimensional magnetic field evolution in a plasma opening switch (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 792-798 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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(approximately-less-than)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. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872766
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  • 4
    Electronic Resource
    Electronic Resource
    Spectroscopic investigations of the plasma behavior in a plasma opening switch experiment (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2122-2137 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871299
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  • 5
    Electronic Resource
    Electronic Resource
    Spectroscopic investigation of fast (ns) magnetic field penetration in a plasma (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2583-2589 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The time-dependent magnetic field spatial distribution in a coaxial positive-polarity plasma opening switch (POS) carrying a current (approximately-equal-to)135 kA during (approximately-equal-to)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 (approximately-equal-to)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. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871220
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  • 6
    Electronic Resource
    Electronic Resource
    Plasma flows and fluctuations in intense ion-beam diodes (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 758-763 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A possible source of electric field fluctuations in the anode plasma of a magnetically insulated ion diode which have been observed in recent experiments is discussed. It is suggested that these fluctuations are driven by the ion flow which destabilizes an electrostatic mode akin to two-stream instability. Evidence is presented for such a flow and its implications for the electric field polarization and magnitude are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870767
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  • 7
    Electronic Resource
    Electronic Resource
    Visible-light spectroscopy of pulsed-power plasmas (invited) : Proceedings of the 9th topical conference on high temperature plasma diagnostics (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 5127-5131 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: 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 are studied during the implosion phase. Radial velocity distributions are observed from the line Doppler shifts and widths.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143461
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  • 8
    Electronic Resource
    Electronic Resource
    Spectroscopic determination of the magnetic-field distribution in an imploding plasma (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 1068-1075 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The time-dependent radial distribution of the magnetic field in a high density z-pinch plasma has been determined by observation of the contribution of the Zeeman effect to the spectral profiles of ionic emission lines. The dominance of the line profiles by the Stark broadening required high-accuracy profile measurements and the use of polarization spectroscopy. The plasma implodes in (similar, equals)600 ns, and the field distribution was measured up to 90 ns before stagnation on axis. During the implosion the plasma was found to conduct the entire circuit current. By comparing the data to the solution of the magnetic diffusion equation the electrical conductivity of the plasma was determined, found to be in agreement with the Spitzer value. These measurements, together with our previously measured ion velocity distributions, allowed for the determination of the time-dependent relative contributions of the magnetic and thermal pressure to the ion radial acceleration across the plasma shell. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872637
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  • 9
    Electronic Resource
    Electronic Resource
    Novel gas-doping technique for local spectroscopic measurements in pulsed-power systems (1998)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 1529-1533 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A novel method for doping plasmas in pulsed-power experiments with gaseous elements has been developed. A fast gas valve, a nozzle, and a skimmer are used to generate an ultrasonic gas beam that is injected into a planar-geometry microsecond plasma-opening switch (POS). An array of ionization probes with relatively high spatial and temporal resolutions was developed for diagnosing the absolute injected-gas density and its spatial profile. The properties of the gas column were also studied using spectroscopy of line emission that results from the interaction of the doped gas with the POS prefilled plasma. The doped column is found to have a width of (approximate)1 cm and a density of (0.8–1.7)×1014 cm−3. Observations of characteristic emission lines from the doped atoms and their ions allow for various spectroscopic measurements, such as the magnetic field from Zeeman splitting and the ion velocity distributions from Doppler shifts, that are local in three dimensions. It is shown that this gas doping technique can also be used to study proton-dominated plasmas that cannot be studied with simple emission spectroscopy due to the lack of light emitting ions. The variety of gases used with this method, together with the small valve dimensions and its fast opening, make it potentially useful for broad diagnostics of various short-duration plasma experiments. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148791
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  • 10
    Electronic Resource
    Electronic Resource
    Measurements of ion transverse-velocity distribution in the gap of an ion-beam diode (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 4781-4785 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have measured the distributions of ion transverse velocities in the acceleration gap of a magnetically insulated ion diode. The measurement is based on observing the spectral profile of the Doppler-broadened spontaneous line emission from accelerating ions. The velocity distributions of C++ and Al++ ions were peaked at zero transverse velocity and symmetric with respect to the directions parallel and antiparallel to the magnetic-field lines. The mean transverse velocities for both of the ion species corresponded to energies of about 200 eV in experiments with a gap potential difference of 260–330 kV. The divergence angles observed for both of the ion species are significantly smaller than previously observed for protons outside the diode.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.338816
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