Study of Fast Magnetized Turbulent Plasma Flow Past Obstacles in a Wind-Tunnel Laboratory Experiment

Turbulence can be found in systems with fluids flowing past or around objects embedded within that flow. This is true of conventional fluids such as liquids like water or gases like air, and is also true of plasmas. This award supports a study of the impact different types of obstacles make on turbulent, magnetized plasma flow in a tunnel vacuum chamber.

Since plasma can interact with electric and magnetic fields, the targets in these experiments can be both solid objects made of material such as ceramic, or magnetic field structures generated either by permanent magnets or by driving current through wires crossing the chamber. Interpretation of measurements made in these experiments can be used to help better understand naturally occurring instances of magnetized plasma flowing past obstacles.

A prime example of such plasma is the solar wind flowing by both non-magnetic objects like the Moon and magnetic obstacles like the Earth’s magnetosphere, where the new understanding can contribute to space weather prediction both here on Earth and on other planets. This work can also be important for better characterization of the plasma flow interactions with potentially vulnerable human-made objects such as spacecraft or satellite constellations.

The project will also have an important workforce development component in engaging and training the next generation of plasma scientists at both graduate and undergraduate level to contribute to the US national security and economic prosperity in their future careers.

This award supports an experiment with a coaxial plasma gun launching a turbulent magnetized plasma at high speeds down a 0.25m wide, 2.5m long cylindrical vacuum chamber. The experimental plasma and flow parameters will be varied from low-to-high beta values as well as from sub-to-super Alfvenic or Mach numbers. Embedded within this flow will be obstacles which can interact with and modify the flowing plasma as well as affect the characteristics of the observed turbulence within the plasma.

These obstacles can be solid objects made of either insulating non-magnetic materials such as ceramic or conducting non-magnetic materials such as copper; or magnetic field configurations including axial field generated by pulsed current in a straight wire traversing the diameter of the chamber or dipole fields produced by pulsed current through wire coils or with strong permanent magnets. Differences in the resulting turbulence characteristics will be explored via several analysis techniques including spectral decomposition, correlation, and intermittency analysis.

Measurements will be made using inserted probes as well as via non-invasive spectroscopic methods, with comparisons to naturally occurring plasma flow obstacle encounters such as bow shocks, magnetotails, or depletion wakes to be pursued within the experimental system.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.