Determining d 2 I/dV 2 from a traditional Langmuir probe trace using numerical techniques is inherently noisy and generally yields poor results. We have developed a Langmuir probe system based on a method first used in the 1950's by Boyd and Twiddy [1]. The system measures the 2nd derivative directly. This paper presents results from the driver and extraction regions of the KAMABOKO III ITER like negative ion source.
