Investigation of Critical Ionization Velocity in a Rapidly Rotating Plasma*

Rapidly rotating plasmas show promise in applications such as fusion energy and large-scale x-ray generation because of their potential to confine plasma in a magnetic mirror configuration and the tendency of the shear velocity to mitigate instabilities from forming [1].  The Maryland Centrifugal Experiment (MCX) was a magnetized rapidly rotating plasma experiment that demonstrated many of the potential benefits of centrifugal confinement, but was ultimately limited by the Critical Ionization Velocity (CIV) and the device insulators and was therefore unable to demonstrate the full potential of the confinement scheme. [2].  CIV is the velocity, in this case the rotational velocity of the plasma, when exceeded, a neutral traveling through a magnetized plasma will rapidly ionize [3].  A second generation of MCX is being developed at the AFRL to explore CIV phenomena further.  There are two primary objectives of this experiment, the first being to pinpoint the neutral density needed for CIV to occur.  There is no minimum density of neutral seed gas listed in the literature and this would be useful knowledge in the field of rapidly rotating plasmas.  The second objective is to determine if and where, on the magnetic field lines, the plasma is CIV-limited.  The experimental design has been modified from MCX to be able to explore this, most likely with spatially resolved fluorescence spectroscopy.

 

[1] C. A. Romero-Talamas, R. C. (2012). Isorotation and differential rotation in a magnetic mirror with imposed EXB rotation. PHYSICS OF PLASMAS, 19(7).

[2] Remington Reid, D. D. (2020). Velocity Limits and Positive Probes in ExB Drifting Plasmas. AFSOR Program Review.

[3] Lai. (2001). A REVIEW OF CRITICAL IONIZATION VELOCITY. Hanscom Air Force Base, Massachusetts, Space Vehicles Directorate.