Page 2 - Achievement of Field-Reversed Configuration Plasma Sustainment via 10 MW Neutral-Beam Injection on the C-2U Device

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FIG. 1. (a) C-2U experimental device, (b) Sketch of FRC magnetic topology and density contours, simulated by the 2-D MHD LamyRidge equilibrium code.
Studying aspects of FRC plasma sustainment by neutral-beam (NB) injection (NBI) and additional particle fueling is the main goal of C-2 / C-2U experiments at Tri Alpha Energy. The world’s largest CT device, C-2 [3], has been upgraded to C-2U [4] (illustrated in Fig. 1) to achieve sustainment of FRC plasmas by NBI and edge biasing. One of the key accomplishments of the C-2 experiments was the demonstration of the high-performance FRC (HPF) regime, which is set apart by dramatic improvements in confinement and stability compared to other FRC devices [4-7]. C-2’s HPF plasma discharges have also demonstrated increasing plasma pressure and electron temperature, which indicates an accumulation of fast ions as well as plasma heating by NBI. Electrically biased end-on plasma guns and effective in-vessel wall-surface conditioning also played important roles in producing HPF plasmas, synergetically with NBI.
In order to enhance fast-ion effects and further improve FRC performance towards plasma sustainment, the C-2U experiment is characterized by the following key system upgrades: increased total NB input power from ~4 MW (20 keV hydrogen) to 10+ MW (15 keV hydrogen) with tilted injection angle as shown in Fig. 1, and enhanced edge-biasing capability inside of each end-divertor for boundary/stability control. The upgraded NB system (higher NB input power with high current at lower beam energy, angled and tangential co-current injection) alone has demonstrated significant advantages and had a profound impact on C-2U performance: e.g. reduction of peripheral fast-ion losses; increased core heating; rapidly established dominant fast-ion pressure; better NB plasma coupling and reduced shine-through losses; and current drive.
In fact, C-2U experiments with upgraded NBI and edge-biasing systems exhibit far better FRC performance than obtained in C-2 HPF regimes [8]. As anticipated, there are strong effects of the considerable fast particle population: (i) rapid accumulation of fast ions (about half of the initial thermal pressure replaced by fast-ion pressure); (ii) fast-ion footprint largely determines FRC dimensions; (iii) double-humped electron density and temperature profiles (indicative of substantial fast-ion pressure); (iv) FRC lifetime and global plasma stability