Measurement of blob-like structure behavior in the plasma edge in QUEST

Measurement of blob-like structure in the boundary region of ECRH plasmas in a simple magnetic configuration in QUEST (major radius, R = 0.68 m, minor radius, a = 0.40 m and toridal magnetic field, Bt = 0.25 T at R = 0.64 m) using combination of a fast imaging camera with a movable and rotatable Langmuir probe system was presented. The blob-like structures, which had an elongated structure along the magnetic field line and moved in the radial direction, were observed. The observed 2-D evolution of these structures strongly depended on the value of Bz/Bt, where Bz shows vertical magnetic field. Ion saturation current was asymmetric in terms of time when the blob-like structure was passing. This means that plasma in the blob-like structure hunches over, which is the same of blobs in other devices [G. Y. Antar et al., Phys. Rev. Lett. 87, 065001 (2001)]. The typical radial velocity of the blob-like structure is ~ 1km/s. Average amplitude of electron density and electron temperature of the blob-like structures are as large as 4 times and 1.6 times those of the background plasma value, respectively.