Initial Result of Successive SXR Imaging Measurement in Low-A RFP

Abstract

A fast successive soft-X ray (SXR) imaging system where SXR camera and high-speed camera for the study of time evolution of magnetic islands has been constructed. A preliminary experimental result in which we observed tangential SXR images from quasi-periodic quasi-single helicity (QSH) state in low-aspect-ratio (low-A) reversed field pinch (RFP) is presented. We successfully obtained time evolution of SXR images from tangential port. By comparison obtained images with simulated images, we may conclude that the evolution of experimental SXR image suggests the rotating QSH RFP configuration. The filamentous configuration tends to be observed in QSH state rather than in multi-helicity (MH) state.

Measurement and Evaluation of 3-D Structure in Low-Aspect-Ratio RFP RELAX with Dual SXR Imaging System

“…3 (b), assuming radial position of rational surface r s is located on 10 cm. Detail explanation of the procedure of calculation has been reported elsewhere [12,13]. By comparing them, we see clearly that two distinguished SXR emissivity structures are realized in QSH and MH discharge, respectively.…”

“…2-D SXR images are recorded with individual high-speed cameras (Photoron FASTCAM SA-4 and SA-X). Detailed designs and characteristics of tangential and vertical SXR cameras have been reported in elsewhere [12,13]. The SXR images have shown a strong dependence on the field reversal parameter F, defined by the ratio of the edge toroidal field B φ (a) to the average toroidal field < B φ >, which represents the degree of toroidal field reversal.…”

Design and Initial Result of Time-Resolved Vertical Soft X-Ray Imaging System in Low-<i>A </i>RFP

“…Moreover, we have constructed a fast successive SXR imaging system. As a preliminary experiment, we have taken tangential SXR pin-hole pictures with a time resolution of 10 µs in order to identify the time evolution of a simple helix structure in RELAX plasmas [8,9]. As the next step, we have developed an SXR imaging diagnostic system that uses multiple pin-hole SXR cameras together with high-speed cameras to record the time evolution of the SXR images from the tangential and vertical directions simultaneously for studying the dynamic structures of 3-D SXR emissivity.…”

Characterization of Quasi-Single-Helicity States in a Low-Aspect-Ratio RFP

“…RELAX is a low-A RFP machine to explore the characteristics of low-A RFP configurations. Initial results from RELAX on QSH have been reported particularly with emphasis on imaging diagnostics [5][6][7][8]. In this paper, major characteristics of QSH in RELAX (i.e., low-A RFP) is discussed based on major magnetic diagnostics results.…”