Characteristics of the First H-Mode Discharges in the National Spherical Torus Experiment...

We report observations of the first low-to-high (L-H) confinement mode transitions in the National
Spherical Torus Experiment. The H-mode energy confinement time increased over reference discharges
transiently by 100 200%, as high as
100 ms. This confinement time is
2 times higher than predicted
by a multimachine scaling. Thus the confinement time of spherical tori has been extended to a record
high value, leading to an eventual revision of confinement scalings. Finally, the power threshold for
H-mode access is .103 higher than predicted by an international scaling from conventional aspect-ratio
tokamaks, which could lead to new understanding of H-mode transition dynamics.