Y. Miura et al., RAPID CHANGE OF ION ENERGY-DISTRIBUTION AND FLOATING POTENTIAL AT L HTRANSITION IN THE JFT-2M TOKAMAK/, Plasma physics and controlled fusion, 36(7), 1994, pp. 10000081-10000086
Rapid changes of the main ion energy distribution at transitions from
L-to-H, H-to-L and during ELMs are studied with the time of flight neu
tral measurement in the JFT-2M tokamak. At the L to H transition, 200-
400 mus prior to the start of H(alpha) drop, an increase of the high e
nergy neutral flux above an energy of 200eV is observed. An energy of
higher than 200eV for hydrogen corresponds to the collisionless condit
ion v(i)<1 just inside the separatrix. The change of the main ion ene
rgy distribution after sawtooth crash during an L-mode phase is also s
tudied. The change of the ion energy distribution just after sawtooth
crash is the same as that at L/H-transition. The floating potential me
asured in the SOL also shows the rapid jump to more positive just afte
r the sawtooth crash (at the same time of the change of an ion energy
distribution). This shows the increase of ion outflux in the SOL and m
ight correspond to the change of the ion energy distribution. This may
be the reason why most of H-modes are triggered by a sawtooth. These
observations support theories predict an important role of ion loss fo
r the L/H-transition.