HIGH-RESOLUTION TOMOGRAPHIC IMAGING OF VACUUM MAGNETIC-SURFACES IN THE H-1 HELIAC

A new, high-precision rotating wire grid apparatus for vacuum magnetic surface mapping of current-free toroidal plasma confinement geometrie s is described. This full-scaled version of the prototype apparatus(1) developed on the SHEILA heliac has been tested and permanently instal led on the H-1 heliac. Data of high quality are obtained with low elec tron energy (<20 eV) to avoid drift errors, with submillimeter resolut ion and accuracy, within a 700 mm circular field of view. The apparatu s avoids pixcell resolution Limits and optical distortion, and is show n to be highly suited to precise comparison of computed and experiment al magnetic surfaces, and after tomographic inversion, can produce use ful images of the magnetic surfaces. (C) 1997 American Institute of Ph ysics.