OHMIC H-MODE POWER THRESHOLDS AND RECYCLING ON COMPASS-D

Single null X-point discharges on COMPASS-D show a gradual L to H tran sition. Frequent boronization gives long ELM-free H-mode periods, dura tion > 100 ms, with continuously rising density to > 1.5 X 10(20) m(-3 ). The L-H transition threshold behaviour is more complex than that pr edicted by present simple scaling laws, with a well-defined low-densit y limit being observed and sensitivity to small perturbations at the p lasma boundary. Density and recycling behaviour is analysed. In discha rges refuelled by recycling alone, the coefficient of recycling as wel l as the particle confinement time is higher in H-mode periods.