Stability of field-reversed configurations in the large s experiment (LSX)

Data from several diagnostics employed on the Large s Experiment (LSX) field‐reversed theta pinch were analyzed to seek correlation between plasma distortions and the confinement properties of the field‐reversed configurations (FRC’s) formed. In particular, an array of Bθ probes was used to determine separatrix movement, which might indicate the existence of low‐order modes, such as a tilt instability. No correlation between the quality of confinement and signal was observed. The parameter s, equal to the average number of ion gyroradii inside the separatrix, has been postulated as a measure of FRC stability with values above 2, leading to instability and loss of confinement. However, the confinement observed in experiments conducted over a large range of s (1