Movable multi-probes for plasma boundary measurement in sino-united spherical tokamak

A novel movable multi-probes is developed to get local magnetic and electrostatic profiles on Sino-UNIted Spherical Tokamak (SUNIST). This multi-probes combines a four-tips Langmuir probe, a magnetic coil, and a retarding field energy analyzer (RFEA). It can be used to simultaneously measure the poloidal magnetic field B-p, electric field E-r, electron temperature T-e, electron density n(e), and ion temperature T-i. Its small overall size (20 x 20 x 38 mm(3)) enables the movable multi-probes to measure the magnetic and electrostatic profiles in high spatial resolution, with negligible impact to plasma in SUNIST. This paper presents the design of the movable multi-probes, in particular, details of RFEA for reliable ion energy measurements. Preliminary experimental results of the movable multi-probes are given as well. (C) 2014 AIP Publishing LLC.