Magnetic surface optimization on the Auburn Torsatron

Magnetic surface optimization studies have been conducted on the Auburn Torsatron. Winding errors in the original helical field coil resulted in a displacement and an up-down asymmetry in the magnetic surfaces. The displacement was initially corrected by unbalancing the outer Helmholtz coils. Computer modelling showed that the observed displacement and asymmetry are expected for a helical field coil winding error having a cos (θ) modulation. A helical correction coil with the appropriate modulation was designed and installed. Magnetic surface mappings with and without the helical correction coil were conducted. With the correction coil, there was a significant improvement in surface symmetry. The experimental results are in good agreement with the predictions of the computer modelling.