Design and Implementation of Langmuir Probe Arrays for Non-Resonant Divertor Studies in the Compact Toroidal Hybrid Experiment

Modeling studies of the non-resonant divertor concept applied to the Compact Toroidal Hybrid (CTH) have shown a resiliency of the plasma strike lines to internal plasma currents. To this effect, two Langmuir probe (LP) arrays are being constructed for insertion into the non-axisymmetric plasma of CTH to validate the non-resonant divertor concept and measure the strike lines of 3D magnetic equilibria where the edge topology is altered by varying the internal plasma current. Both arrays will consist of ~10 probes spaced ~1 cm apart and will be positioned at both the half-field period and the limiting surface. The probes are located where the measured ion flux is expected to change as the plasma transitions from a limited LCFS to a stochastic boundary. The single-tipped LPs are constructed from 1 mm diameter molybdenum pins shielded by 5 mm diameter BN sleeves, and will be biased into the ion saturation regime with sampling rates of 500 kHz. CTH edge plasmas are expected to vary in density from 10¹⁷ to 10¹⁸ m^-3 with electron temperatures of 5-10 eV. Initial experimental measurements of the edge plasma ion fluxes will be presented.