Design and initial result of time-resolved vertical soft x-ray imaging system in low-A RFP

A time-resolved vertical soft X-ray (SXR) imaging system was constructed. To identify the structure of the magnetic island using the obtained SXR images, we calculated the two-dimensional (2-D) image expected from low-aspect-ratio (low-A) reversed field pinch (RFP) plasmas. The 2-D image was found to reflect the change in the radiation power caused by the magnetic island. A preliminary experimental result in which we observed vertical SXR images fromthe quasi-periodic quasi-single helicity (QSH) state in low-A RFP plasmas is presented. We successfully obtained the time evolution of SXR images from the vertical port. By comparing the observed images with simulated images, we found that the evolution of the experimental SXR image suggests a rotating helical configuration.