Edge Plasma Flux Measurements for Characterization of Non-Resonant Divertor Behavior on the Compact Toroidal Hybrid Experiment

Modeling studies investigating the non-resonant divertor concept have demonstrated resiliency of the plasma strike line locations to large changes in the equilibrium flux surface structure of CTH plasmas. To validate these predictions and characterize strike point locations for specific non-axisymmetric 3D magnetic equilibria, two Langmuir probe (LP) arrays have been developed for ion flux measurements at the edge of CTH plasmas. These LP arrays consist of a radially movable array with 25 probes positioned at the half-field period, and a fixed array with 12 probes at a limiting surface. Each array covers ~1 radian of poloidal extent and measures ion flux at a sampling rate of 500 kHz. These locations are where the measured ion flux is expected to undergo the greatest change when the edge flux surface structure transitions from a limited last closed flux surface to a chaotic edge boundary. This transition, produced by internal plasma current, accompanies field line chaos, loss of edge flux surfaces, and a change in magnetic topology near the half-field period appearing as a helical band that splits into two distinct strike lines. Preliminary measurements of the edge ion fluxes will be presented alongside the anticipated strike line positions derived from previous modeling efforts.