1 - Nuclear Sciences and Applications - IAEA

196 BURRELL et al.
used in the initial experiments [2]. The similar ne and BT dependence of
Pth is consistent with Ohyabu's microtearing mode theory of the L to H
transition [4].
ECH appears to be more efficient than NBI at producing the Hmode.
The lowest threshold seen to date is Pth = 0.8 MW for ECH in a
deuterium plasma at IP = 0.5 MA, BT = 1.1 T and ne = 1 X 10 19 m~ 3 [5];
the NBI threshold for this case is about 1.1 MW. Ohmic heating can
also produce the H-mode. As indicated in Fig. 1, the threshold power
for Ohmic H-mode is consistent with that for NBI-produced H-modes.
Achieving Ohmic H—mode requires high currents (>1.2 MA) at low toroidal
field (