Search NASA⌕ Search

Engineering topics

Dowhan, G. V.

Publications and source records attributed to Dowhan, G. V..

4 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

High-Magnification Faraday Rotation Imaging and Analysis of X-pinch Implosion Dynamics

An X-pinch load driven by an intense current pulse (>100 kA in ~100 ns) can result in the formation of a small radius, runaway compressional micro-pinch. A micro-pinch is characterized by a hot (>1 keV), current-driven (>100 kA), high-density plasma column (near solid density) with a small neck diameter (1–10 μm), a short axial extent (<1 mm), and a short duration (.1 ns). With material pressures often well into the multi-Mbar regime, a micro-pinch plasma often radiates an intense, sub-ns burst of sub-keV to multi-keV x-rays. A low-density coronal plasma immediately surrounding the dense plasma neck could potentially shunt current away from the neck and thus reduce the magnetic drive pressure applied to the neck. To study the current distribution in the coronal plasma throughout the implosion process, a Faraday rotation imaging diagnostic (1064 nm) capable of producing simultaneous high-magnification polarimetric and interferometric images has been developed for the 1-MA, 100-ns MAIZE facility at the University of Michigan. Designed with a variable magnification (1–10&times;), this diagnostic achieves a spatial resolution of approximately 35 μm, which is useful for resolving the ~100-μm-scale coronal plasma region immediately surrounding the dense core. Combined with the corresponding interferogram, which provides the radial density distribution in the low-density coronal plasma, the measured rotation can be used to diagnose the delivery of the driver current, and thus the magnetic drive pressure, to the micro-pinch plasma as it approaches minimal radius. Using this technique on MAIZE, we have measured

Dowhan, G. V.↗
DOE OSTI2021

Additively manufactured electrodes for plasma and power-flow studies in high-power transmission lines on the 1-MA MAIZE facility

Power-flow studies on the 30-MA, 100-ns Z facility at Sandia National Laboratories have shown that plasmas in the facility’s magnetically insulated transmission lines (MITLs) and double post-hole convolute can result in a loss of current delivered to the load. To study power-flow physics on the 1-MA, 100-ns MAIZE facility at the University of Michigan, planar MITL loads and planar post-hole convolute loads have been developed that extend into the lines of sight for various imaging diagnostics on MAIZE. These loads use 3D-printed dielectric support structures lined with thin foils of either aluminum or stainless steel. Here, the metal foils serve as the current-carrying power-flow surfaces, which generate plasma during the current pulse. The foil thickness (50 µm) and widths (11.5–16 mm) are selected to ensure a sufficient linear current density (0.5–0.7 MA/cm) for plasma formation. Laser backlighting (532 nm) and visible-light self-emission imaging capture the overall plasma evolution in the anode–cathode gaps, including the gap closure velocities (1–4 cm/μs).

47 OTHER INSTRUMENTATION↗