Study of blob-like structures in QUEST

Abstract Blob-like structures are observed in an open magnetic field line configuration of electron cyclotron resonance (ECR) heating plasma in QUEST. The combined measurement with a fast camera and a movable Langmuir probe show that visible filamentary structures extended along field lines do correspond to over-dense plasma structures. Ion saturation current time trace shows a front-like asymmetric burst when a visible structure reaches the probe during its outward propagation. The typical radial velocity of the blob-like structure, V b , was measured as ∼1 km/s with the fast camera at the intermediate area. V b increased as the blob-like structure moved along major radius, R (outward). The average velocity of E  ×  B drift derived from the probe measurement, slightly larger than V b , was also increased as the blob-like structure propagated to larger R .