Enhanced Stabilization of Internal Tilt Mode by Neutral Beams in C-2W

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 S*/E. Here, S* is the FRC radius divided by the ion inertial length, and E is the FRC elongation. [2] Experimental evidence from numerous FRC devices has suggested that the threshold for the catastrophic tilt is S*/E ~ 3. C-2W has demonstrated an ability to maintain values of S*/E substantially higher than the prior empirical limit, reaching S*/E ~ 5. Theoretical models have validated the assertion that the finite Larmor size for an FRC with β ~ 1 has a stabilizing effect. In C-2W, the presence of a large fast ion population from neutral beam injection maintains plasma stability above the traditional limit. A series of experiments was conducted to probe the effect the fast ion population on FRC stability, utilizing the variable energy neutral beams (15 - 40 keV, total power up to 20 MW). Results will be presented, demonstrating that the maximum achieved value of S*/E scales with the captured neutral beam power.

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

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