Magnetic Field-Shaping Effects on Tilt Stability in C-2W Field Reversed Configuration

TAE Technologies’ current experimental device, C-2W (also called “Norman”), is an advanced, neutral beam-driven, field-reversed configuration (FRC). [1] Traditional FRCs are known to be theoretically unstable to an internal tilt mode whose threshold is characterized by the parameter S*/E. Here, S* is the FRC radius divided by the ion inertial length, and E is the FRC elongation. [2] Experimental evidence from previous FRC devices has suggested that the threshold for the tilt is S*/E ~ 3. C-2W has demonstrated higher S*/E than this prior empirical limit due to a large population of fast ions from neutral beam injection. Understanding this link between the two will be crucial for any future FRC device. A series of experiments was conducted to change the shape of the FRC and the distribution of fast ions therein by utilizing the field-shaping modularity from fast, external magnetic coils. FRC was found to be stable to the tilt mode for the entire range of mapped space in S* and Elongation. By concentrating the fast ions near the midplane of the device, S* was pushed to its highest levels recorded in C-2W, while lengthening the FRC helps stabilize fast ion-driven modes.

1. H. Gota et al, Nucl. Fusion 59, 112009 (2019).

2. A. Ishida et al, Phys. Fluids, 31, 3024-3034 (1988)