Magnetic Guarding of Octupole Hoop Supports

Magnetic guarding of hoop supports and other obstacles in the Wisconsin octupole reduced the direct loss of plasma to the supports or obstacles by more than an order of magnitude. However, an increased loss rate to the walls and hoops locally around a support offset the reduction in direct loss. Theoretical models based on ion scattering or collective effects were consistent with the magnitude of the increased wall (hoop) loss rate with guarding. But, only the models based on collective effects or associated with the lack of symmetry between each support and the octupole magnetic field were reasonably consistent with the observed scaling of the loss rate with ion temperature and magnetic field.