Dynamic behaviour of the low-to-high confinement transitions in the H-1 heliac

The dynamic behaviour of the plasma parameters, including the local electro n density, electron temperature, plasma potential and their radial gradient s, is studied experimentally during the transitions between low and high co nfinement modes (L-H transitions) in the H-1 heliac. In particular, a dynam ic phenomenon occurring near the threshold conditions for the L-H transitio n and manifesting itself as a quasi-periodic low-frequency modulation of th e local and average plasma parameters is described and discussed. A simple qualitative model for this phenomenon, referred to as L-H cycles, is sugges ted.