Development of a triple Langmuir probe for plasma characterization in SPIDER

The Neutral Beam Test Facility (NBTF) was built at Consorzio RFX (Padova, Italy) to carry out dedicated experiments with the specific purpose of pursuing the requirements of ITER neutral beam injectors. The SPIDER experiment, which is part of the NBTF program, is devoted to the study and optimization of the ion source of the ITER injectors. The present contribution describes the operation of a fixed triple Langmuir probe, which has been recently installed in SPIDER for the investigation of the source plasma. Indeed, this diagnostic is able to measure the time evolution of the main plasma features for the entire duration of the plasma discharge, allowing the correlation between plasma properties, such as density, electron temperature and plasma potential, and source parameters, i.e. filter field intensity, RF power and bias voltages. Furthermore, the capability of the triple probe arrangement of measuring the instantaneous plasma density and electron temperature (also at high frequency) has been exploited to investigate a modulation of plasma parameters, which emerged while operating SPIDER either with multiple generators or with a single generator at low power and with high filter field. The views and opinions expressed herein do not necessarily reflect those of the ITER Organization.