Abstract
Electron-beam wire-tomography in the H-1NF heliac enables high resolution mapping of vacuum
flux surfaces without significant disruption of plasma operations. Recent experimental results have
proved this technique to be a highly accurate and high resolution method for mapping vacuum
magnetic islands. Islands of width as small as 8 mm have been measured, providing estimates
of the internal rotational transform of the island. Point-to-point comparison of the mapping re-
sults with computer tracing, in conjunction with an image warping technique, enables systematic
exploration of magnetic islands and surfaces of interest. Recent development of a fast mapping
technique significantly reduced the mapping time and made this technique suitable for mapping at
higher magnetic fields. This paper presents recent experimental results and associated techniques.
