Characterization of quasi-Keplerian, differentially rotating, free-boundary laboratory plasmas

Vincente Valenzuela-Villaseca

Imperial College, London

Wednesday, November 24, 2021

11:00am

NW17-218

PSFC Seminars

Abstract: This talk will present results from the Rotating Plasma Experiment (RPX) developed on the MAGPIE pulsed-power generator (1.4 MA, 500 ns duration). The experimental platform drives plasma flows relevant to astrophysical accretion disks and axial jets in a free-boundary experiment. The goal is to interpret and model the rotation profile and pressure balance of differentially rotating plasmas inertially driven by the slightly off-radial inward-convergence of 8 magnetized plasma jets.

The data shows that rotating plasmas have a hollow density structure and are radially confined by the ram pressure of the ablation flows. A combination of axial thermal and magnetic pressure launches an axial, highly collimated, supersonic jet with a velocity ~ 100 km/s (M > 5). The axial jet also rotates, transporting angular momentum, as it remains collimated by a hot (T_i ~ 250 eV) surrounding plasma halo. It is inferred that the plasma halo is magnetized by a ~ 5 T magnetic field. I will discuss the thermal and magnetic structure of the halo and its impact on jet collimation. Finally, the rotation velocity radial distribution such that angular frequency decreases with radius, as the opposite happens to angular momentum. The calculated squared epicyclic frequency of the flow is estimated to be k² ~ r^-2.8 > 0. This implies that the flows at RPX are quasi-Keplerian and share stability properties of gravitationally driven accretion disks.