Studies of Non-Resonant Divertor Strike Line Resiliency in the Compact Toroidal Hybrid

Two new Langmuir probe arrays have been installed in the Compact Toroidal Hybrid (CTH) experiment to study the strike line behavior of non-resonant divertor-like plasmas while changing the plasma equilibrium with the addition of plasma current. These arrays, located at the half-field period midplane and by a limiting surface, are placed where modeling (Garcia et al. Nucl. Fusion 2023) predicts the plasma flux undergoes the greatest change when transitioning from a limited last closed flux surface to a chaotic edge magnetic boundary. This transition is predicted to be accompanied with changes in magnetic topology via field line chaos and loss of edge flux surfaces near the half-field period. The resulting flux appears as a helical band that splits into two distinct plasma strike lines. For CTH experimental configurations, the helical band splitting is observed after the plasma current surpasses 35 kA and the edge transform exceeds ∼2/3. Electron density profile measurements indicate a substantial loss of edge confinement during the creation of this chaotic edge boundary. For plasma currents up to 65 kA, measurements of plasma flux at the vessel and limiter exhibit a resiliency in the strike line locations.