Z-effective measurements using visible Bremsstrahlung radiation during impurity injection experiments in C-2W

The C-2W fusion experiment [1] at TAE Technologies is an advanced experimental device for creating field-reversed configuration (FRC) plasmas. The FRCs are produced using neutral beam injection, edge biasing, and fueling with hydrogen pellets, compact-toroids, and neutral gas. The plasma also contains impurities, and to enhance understanding of impurity transport in C-2W a study was conducted in which gas impurities were edge-injected. An optical mount collected line-integrated emission from 15 chords along a radial plane through the plasma center. For each view a photomultiplier tube and narrow bandpass filter (~523nm) sampled the visible background Bremsstrahlung radiation. [2] These line integrated measurements were inverted into local profiles and utilized with electron temperature and density from Thomson scattering and far-infrared interferometry to provide time-resolved radial Z-effective profiles. Injection of impurities of higher Z at the plasma edge resulted in an increase in Z-effective at the plasma core, suggesting both parallel transport along the FRC scrape-off-layer and radial transport through the FRC separatrix.

1. H. Gota et al., Nucl. Fusion 61,106039 (2021)

2. M. Nations et. al., RSI 89, 10D130 (2018)