Heavy ion beam probe diagnostic system for ATF

The potential structure in non-axisymmetric toroidal confinement devices is largely responsible for the particle drift surfaces. A heavy ion beam probe diagnostic, which can directly determine the potential, is thus planned for ATF. The most significant device characteristics affecting the implementation of such a system on this complex magnetic geometry that were not encountered on tokamaks are the large toroidal separation (15 degrees) of vertical and horizontal ports and substantial magnetic return fields in the region of the ion optics and energy analyzer electric fields. The status of the design is presented with particular emphasis on the choice of energy analyzer required by the large dispersion in ion trajectories produced by this field