Abstract
A movable magnetic probe array is installed on the compact helical system (CHS) heliotron/torsatron to study Alfven eigenmodes exited by energetic beam ions. The array consists of six sets of magnetic probes for measurements of radial and poloidal magnetic field fluctuations. This probe array is put inside a thin stainless pipe protected with a c/c-composite carbon sleeve containing 20% boron. The carbon sleeve also acts to minimize deleterious effects on a plasma, evaporating boron during a plasma shot. By using this probe array, radial profiles of magnetic fluctuations in the range of f<200 kHz can be obtained even inside the last closed flux surface up to 〈r〉/〈a〉∼0.8 without serious disturbances to the neutral beam injection (NBI) heated CHS plasmas. High frequency magnetic fluctuations less than 200 kHz related to the toroidal Alfven eigenmodes (TAE) are detected with these magnetic probe arrays in NBI heated plasmas. The mode numbers of the observed TAE can be successfully determined by combination of the radial profiles of fluctuations obtained with the movable probe array and a set of poloidal and toroidal arrays of Mirnov probes.
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