Expanding Plasmas

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The Plasma Bubble Expansion eXperiment (PBEX) project will conduct laboratory experiments and coordinated numerical modeling addressing outstanding plasma physics issues related to how magnetic energy and helicity carried by extra-galactic jets reaches quasi-equilibrium with the surrounding intergalactic medium. The experiments will study the relaxation of a magnetized plasma “bubble” as it expands into and reaches equilibrium with a lower pressure background plasma. The primary scientific objectives are to characterize the underlying nonlinear plasma physics of the bubble relaxation process. These nonlinear plasma physics issues cannot at present be resolved from numerical computation or astronomical observations alone; laboratory experiments are needed.

The PBEX Experiment

First Plasma!!!

First plasma obtained with PBX gun, Aug. 7, 2008

To model jet formation we plan to expand a dense magnetized plasma into a diffuse background plasma. A coaxial plasma gun forms and injects magnetized plasma into HelCat vacuum chamber. This bubble interacts with background plasma from helicon or cathode source. Fast cameras, spectroscopic diagnostics, and 2D arrays of magnetic and Langmuir probes will measure the evolution of plasma parameters.

The experiment proceeds as follows:

1. Gas puff valve injects large quantity of gas in short burst (~ few ms)


2. Paschen breakdown along bias field between electrodes forms plasma


3. Field-aligned current injects toroidal flux into plasma


4. External magnetic bias provides trapped poloidal flux


5. J x B forces accelerate plasma out of gun


6. Bias field reconnects as plasma leaves gun, forming closed flux surfaces

Schematic of the PBEX and coaxial gun.

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