Multipoint measurements employing a microwave interferometer and a Langmuir probe in the detached linear plasma

Multipoint measurements were carried out by employing a microwave interferometer (MI) and a Langmuir probe (LP) in steady-state detached plasmas in the linear plasma device NAGDIS-II to reveal the structure of fluctuations along the magnetic field. We changed the LP position along the magnetic field while the MI was fixed at an upstream position. In addition, a fast framing camera was used to identify an azimuthal mode number, and the predominant mode number was identified as m = 1. By analyzing correlations between signals observed by the LP and the MI, it was found that a time delay of 10–20 kHz fluctuations gradually decreased toward the downstream direction. The results indicate a decrease in the rotation velocity in the E × B direction, and suggest that the 10–20 kHz fluctuation forms a spiral shape.