Relaxation of spheromak plasmas toward a minimum-energy state and global magnetic fluctuations

Globally coherent modes which are observed during formation in the S-1 Spheromak plasma occur during flux conversion and plasma relaxation toward a minimum-energy state, suggesting that these modes provide a means for relaxation. A significant finding is the temporal progression of these modes through a sequence n=5,4,3,2, m=1, as q rises through rational fractions m/n, where n and m are defined by the functional dependence $e^{i(n\phi +\mathrm{mtheta})}$ of the fluctuations on toroidal angle φ and poloidal angle theta. Comparison with theory of the observed modes and the sequence of occurrence suggests that these modes are due to resistive MHD instabilities.