Local variables affecting H-mode threshold on alcator C-mod

An edge temperature threshold for the LH transition is found on the Alcator C-Mod tokamak. The critical temperature depends weakly on density and increases with B-T and with unfavourable drift direction. T-e at the H-L transition can be greater than or equal to the L-H threshold. Magnetic fluctuations are observed at some H-L transitions. Measured parameters are compared with H-mode theories, including nonlinear drift-ballooning code simulations.