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

Experiments using Langmuir probe arrays in the Compact Toroidal Hybrid (CTH) experiment have confirmed the strike line resiliency of non-resonant divertor-like plasmas when changing the plasma equilibrium with the addition of plasma current. Electron density profile measurements show a substantial loss of edge confinement and the creation of a chaotic edge boundary.

Two arrays, one located near a symmetry plane and another attached to a limiter, agree with modeling predictions of the plasma flux location for a chaotic edge magnetic boundary. The measured flux patterns also qualitatively agree with predictions of the transition behavior from a limited to diverted configuration. The plasma flux appears as a helical band split into two distinct plasma strike lines when diverted. These strike line locations can shift by 4cm or less when altering the vacuum equilibrium in addition to changing the relative flux between strike lines. The strike line splitting appears for edge rotational transform values above ∼0.5-0.6, but can vary depending on the vacuum equilibrium and may not appear until the edge transform is ~1. For changes in ohmic plasma currents up to 65 kA and an edge transform of ~1.5, measurements of plasma flux at the vessel and limiter exhibit a resiliency in the strike line locations. The strike lines shift by 2 mm/kA, or 2-4cm over the course of a discharge, and show resilient locations despite edge transform variations of ~0.5.