Summary description:
This research focuses on the creation and dynamic evolution of plasma in low-current X-Pinch devices. We develop an integrated methodology combining advanced experimental optical diagnostics (three-frame shadowgraphy, interferometry) and multiphysics MHD computational simulations (GORGON, PLUTO) to study plasma evolution, plasma jet formation, hot spot generation, and X-ray production for high-resolution radiography applications.
Keywords: X-pinch plasmas, magnetohydrodynamic simulations, plasma jets, X-ray radiography, optical probing diagnostics, plasma instabilities
Detailed overview
The study of X-Pinch plasmas is a fundamental research topic with significant applications in high-resolution radiography of biological samples, dense plasma imaging, and laboratory astrophysics. Our research group develops and applies an integrated methodology combining high-precision experiments and advanced MHD computational models to study the dynamic evolution of plasma from initial expansion to jet formation and X-ray production.
Experimental Approach
We employ a low-current (45 kA, 50 ns rise time) X-Pinch device to heat thin tungsten (W) or gold-plated tungsten (Au-plated W) wires of 5 μm diameter. We developed multi-channel optical probing diagnostics for simultaneous recording of plasma temporal evolution:
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Three-frame Shadowgraphy: Qualitative and quantitative evaluation of plasma instabilities and jet formation.
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Three-frame Mach-Zehnder Interferometry: Measurement of areal electron plasma density.
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Point-projection Radiography: Imaging of internal structures of samples with ~40 μm resolution.
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Filtered PIN Diodes (Al and Cu filters): Time-resolved soft X-ray emission measurements.
Computational Approach
To understand and predict plasma behavior, we develop advanced MHD computational models:
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PLUTO (Modular MHD Code): Simulation with single-fluid approximation, including:
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SESAME equations of state for tungsten and air
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Radiation transport and optically thin losses
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Electrical resistivity models (linear mixture, Spitzer/10)
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Multi-material mixing for plasma-vacuum interface
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GORGON (Eulerian MHD Code): Simulation of plasma dynamic evolution with separate treatment of ions and electrons, considering:
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Conservation laws of mass, momentum, and energy
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Induction equation with displacement current for magnetic field calculation
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Spitzer resistivity and Joule heating
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Optically thin plasma radiation losses
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Applications and Key Findings
Plasma Jet Formation: Simulations revealed that jet formation results from combined action of plasma expansion from the cross-point region and continuous plasma ablation from the X legs. Jet velocity reaches 39 km/s (Mach 4), with the “zippering” mechanism playing a crucial role.
Biological Sample Radiography: The portable X-Pinch device was used for radiography of olive samples, revealing extensive damage from Bactrocera oleae insect with ~40 μm resolution.
Influence of Physical Parameters: Study of electrical resistivity, radiation transport, and optically thin losses showed that radiation transport reduces instability growth rate, while optically thin losses lead to intense Magneto-Rayleigh-Taylor (MRT) instability development with double magnetic field values.
Examples
Comparison between simulated and experimental results of the areal mass density evolution for front and side views in an X-pinch setup.
Biological Sample Radiography. Point-projection radiography application for detection of damage in olive samples.
Temporal Evolution of X-Pinch Plasma. Comparative results of GORGON and PLUTO simulations for plasma density distribution on a slice through the plane of the wires.
Magnetic Field and Temperature Distribution. Comparison of GORGON and PLUTO results for magnetic field, current density, and temperature.
