Date of Award

Spring 2003

Document Type

Restricted Thesis

Terms of Use

© 2003 Andrew Fefferman. All rights reserved. Access to this work is restricted to users within the Swarthmore College network and may only be used for non-commercial, educational, and research purposes. Sharing with users outside of the Swarthmore College network is expressly prohibited. For all other uses, including reproduction and distribution, please contact the copyright holder.

Degree Name

Bachelor of Arts


Physics & Astronomy Department


Axisymmetric plasma configurations which might be used for fusion reactors include tokamaks, spheromaks and field reversed configurations (FRC). The FRC has some advantages over tokamaks and spheromaks, including a high β ≡ (2μ₀P)/(B ². However, compared to tokamaks and spheromaks, relatively little is known about high β configurations like FRC's. This paper is based on a study of a high β spheromak/FRC hybrid configuration in SSX-FRC. The author constructed magnetic probes to measure all three components of the magnetic field vector at 96 locations throughout the hybrid. Measuring the structure of the magnetic field embedded in the plasma is a good way of characterizing the hybrid equilibrium and diagnosing its stability. The magnetics measurements are compared with theory and numerical simulations of axisymmetric toroidal equilibria. In brief, it was found that the hybrid configuration is stable for several characteristic times before tilting. The tilt instability was not observed in studies of counterhelicity spheromak merging by Ono et al [12, 13]. Furthermore, the anti-parallel toroidal fields of the counterhelicity spheromaks in SSX-FRC never completely annihilate, in contrast with the results of Ono et al [12, 13]. However, the persistence of the toroidal field structure is consistent with the simulation results by Omelchenko [32, 33]. The hybrid configuration is not consistent with the general axisymmetric plasma equilibrium (the Grad-Shafranov equilibrium) due to currents that flow across flux surfaces. Controlling the extent to which the spheromaks reconnect with midplane field coils external to the plasma does not have a significant effect on the stability of the plasma configuration.