Publications

Abstract not provided.

Absolute calibration of streaked visible spectroscopy systems has been performed at Z-machine at Sandia National Labs in order to determine temperatures of electrode surfaces during the current pulse. The ability to calibrate the full system, including all fiber optic runs and probes is crucial to understanding errors in the calibration process. The calibration procedure involves imaging a blackbody light source, with a known spectral radiance which is coupled to an integrating sphere. This source is streaked slowly over a few ns using Sydor streak cameras. The slow sweep is converted to a 100-500ns sweep by imaging a bright light source on both sweep rates, and obtaining wavelength and time dependent correction curves. Any broadband light source or several laser lines of differing wavelengths can be used for this correction. This technique has yielded temperature estimates of several eV in the Z convolute.

Abstract not provided.

This LDRD investigated plasma formation, field strength, and current loss in pulsed power diodes. In particular the Self-Magnetic Pinch (SMP) e-beam diode was studied on the RITS-6 accelerator. Magnetic fields of a few Tesla and electric fields of several MV/cm were measured using visible spectroscopy techniques. The magnetic field measurements were then used to determine the current distribution in the diode. This distribution showed that significant beam current extends radially beyond the few millimeter x-ray focal spot diameter. Additionally, shielding of the magnetic field due to dense electrode surface plasmas was observed, quantified, and found to be consistent with the calculated Spitzer resistivity. In addition to the work on RITS, measurements were also made on the Z-machine looking to quantify plasmas within the power flow regions. Measurements were taken in the post-hole convolute and final feed gap regions on Z. Dopants were applied to power flow surfaces and measured spectroscopically. These measurements gave species and density/temperature estimates. Preliminary B-field measurements in the load region were attempted as well. Finally, simulation work using the EMPHASIS, electromagnetic particle in cell code, was conducted using the Z MITL conditions. The purpose of these simulations was to investigate several surface plasma generations models under Z conditions for comparison with experimental data.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Experiments are being performed on the Self-Magnetic Pinch (SMP) electron beam diode on the RITS-6 accelerator at Sandia National Laboratories. This diode produces a tightly focused electron beam (< 3mm diameter) which is incident on a high atomic number bremsstrahlung x-ray converter. Typical diode parameters are 120 kA, 7 MeV, and 70ns current pulse, giving a ~45ns x-ray pulse. Plasmas from contaminants on the electrode surfaces propagate into the A-K vacuum gap, affecting the impedance, x-ray spectrum, and pulse width. These plasmas are measured using diagnostics, which include: spectroscopy, optical imaging, and photon detection; to obtain velocity, density, and temperature information. These parameters are measured both spatially, using multi-fiber arrays, and temporally, using streak cameras and avalanche photodiodes. Plasma densities and temperatures are determined from detailed, time-dependent, collisional-radiative (CT) and radiation transport (RT) models, which include Stark broadening of the hydrogen-alpha transition line and carbon ion line ratios. These results are combined with hybrid PIC/fluid simulations to model the plasma’s overall behavior. Densities of up to 10^19 cm-3 have been measured on the electrode surfaces, decreasing by several orders of magnitude both radially and axially across the vacuum gap. Electrode plasma expansion velocities of up to 10 cm/microsecond correlate well with the decreasing impedance profile (~0.5 Ohms/ns) observed during the pulse.

Abstract not provided.

Abstract not provided.

Abstract not provided.