Development of sweeping detector phase contrast imaging in Large Helical Device

Abstract

Phase contrast imaging (PCI) has been used for the turbulence profile measurement in Large Helical Devices; however, it does not have sufficient spatial resolution owing to the small number of two-dimensional (2D) detector elements. Therefore, in this study, we limited the measurement target to steady-state plasmas and conduct a pseudo multichanneling of a 2D detector array by sweeping using a one-dimensional detector. This new system is called SD-PCI. SD-PCI needs two detectors, one is one-dimensional detector and the other is single channel detector. By selecting suitable detector and imaging magnification for target turbulence or device characteristics, SD-PCI demonstrates the potential capability and enhancements. The wavenumber spectra comparison from the correlation calculations of the simultaneous measurement of the actual plasma with conventional 2D-PCI and proposed SD-PCI shows that SD-PCI is as effective as 2D-PCI in spectral broadening. The simplicity of the proposed system is expected to be applicable to various devices. In this paper, the SD-PCI system was explained along with the initial results of the 2D wavenumber spectrum calculation, which was necessary for obtaining turbulence profile.