Drift surface axis position and transform measurements in the Compact Auburn Torsatron

In toroidal plasma confinement devices, the highly energetic fusion products will have trajectories defining drift surfaces that deviate considerably from the magnetic surfaces. An understanding of these drift surfaces is important for efficient operation of a fusion reactor. By appropriate choice of electron energy on the Compact Auburn Torsatron [Fusion Technol. 18, 281 (1990)], normalized drift surface shifts similar to those for fusion products in a reactor can be studied. As a benchmark, a set of experiments have been conducted to study the axis position and central rotational transform associated with varying vertical fields. Corresponding experiments have been conducted which measure the axis position and central transform associated with the drift surfaces of highly energetic electrons. These experiments were compared and a theoretical model incorporating the spatial nonuniformity of the applied vertical magnetic field was developed. The experimental results agreed well with this theory