Escaping ion measurement with high time resolution on CHS

Abstract

A scintillator-based lost ion probe can measure the temporal evolution of both the gyroradius and the pitch angle of energetic ions escaping a magnetically confined plasma. For the probe on the Compact Helical System, the time resolution of this detailed two-dimensional measurement is determined by a framing rate of the video camera that records the luminous images produced by the ions striking the scintillator plate. The framing rate of the old camera was 30Hz, thus the time resolution was about 33ms. Our interest is to understand the energetic ion transport in fast events such as a bursting energetic ion driven mode. The typical time scale of these events is less than 1ms, meaning that the old camera was too slow. By replacing it with an image-intensified high-speed video camera system, the temporal resolution was improved from 33to0.07ms. We have successfully installed the fast camera and captured some fast events caused by magnetohydrodynamics, which were unobservable using the original camera.