**2.4 The spheromak configuration**

Early experiments in toroidal pinch configurations exhibited, under certain conditions, the spontaneous reversal of the toroidal field near the wall of the chamber. This unexpected feature was succesfully explained in terms of the relaxation theory proposed by Taylor (1974). According to this theory, MHD fluctuations cause the plasma to minimize its magnetic energy while conserving the total magnetic helicity (see Sec. 4).

Some years later, it was realized that the minimum energy state, for a given amount of magnetic helicity, inside a sphere is a system of nested toroidal magnetic flux surfaces (Rosenbluth & Bussac, 1979). The idea of a configuration relevant for fusion research that would be self produced (or self-organized) inside a simply connected volume attracted the attention of the scientific community. Several experiments were designed in order to check this theoretical prediction. The success of these experiments was considered a proof of the remarkable robustness of the relaxation theory (Bellan, 2000).

Despite the initial enthusiasm, it was later realized that the relaxation process involves MHD fluctuations that strongly degrade the confinement. Because of these fluctuations the confinement peformance of the spheromak is much lower than that of the tokamak or the RFP. Little is known about the dynamics of these fluctuations since the relaxation theory is only able to predict the final state of the plasma but it can not provide any detail on how this state is attained (Jarboe, 2005).
