Improved Langmuir Probe Array for DIII-D

Langmuir probes are commonly used plasma diagnostics measuring localized floating potential, electron temperature, particle flux, and electron density. A major upgrade of DIII-D´s lower divertor required an improved design of Langmuir probe arrays to accommodate the higher heat fluxes incident on the new divertor plasma facing components. It was also advantageous to decrease the linear spacing between electrodes and to improve the ease of maintenance. The new electrode design distributes the heat flux almost uniformly over its surface because of the fixed angle roof-top shape. The advanced design features 16 x increased thermal mass half the peak heat flux. Thermal coupling of the probe to the surrounding tile was greatly enhanced by increasing the thermal contact area. A novel probe mounting system has the entire probe array supported in a single tray. After an annual operational period, the probes yielded reliable data and showed little or no erosion.