Control of Runaway Electrons (REs) have been investigated for killer pellet shut down scenario. A neon-ice pellet with 4mm diameter x 4mm length was injected with a velocity of 600~950 m/s. The REs tails were usually generated at the killer pellet injection. Burst-like MHD activities produced by DCW (Disruption Control Winding), where the DCW mainly produced 3/2 and 2/1 modes during the current quench, were effective to suppress the generation of REs. The amplitude of the error field by DCW more than 0.12-0.14% of toroidal field at the plasma center was necessary to suppress REs.
A quasi-steady-state ITER-like ELMy discharges at Ip=1.8MA was sustained for 0.7 s by high triangurality operation (delta ~0.3, q95 ~ 3.4), which is two times as long as the energy confinement time. The normalized beta and the H-factor were 2.7-2.9 and ~2.5, respectively.
The H-mode threshold studies has been developed by ICRF heating. The H-mode transition was observed even when some of the threshold NB power for H-mode transition was replaced by the ICRF power. This result indicates that ICRF power is almost equivalent to NB power for the H-mode transition.
A test injection of 350 keV N-NB (Negative-ion based Neutral Beam) with a power of ~2 MW was attempted into reversed shear plasma heated by a 13 MW of P-NB pulse. Significant increase in neutron emission and the stored energy was observed. The beam-thermal component of the neutron emission increases by a factor of ~2.5. The decay time of the neutron emission after the N-NB is consistent with the classical slowing down of injected beam ions. Enhancement of beam stopping cross section through the multi-step ionization process is under analysis.
BOUNDARY AND STEADY STATE OPERATION PHYSICS
The density profile was measure during divertor detachment by Thomson scattering measurement. When the divertor was detached, edge density at r/a<0.9 was reduced. Transport behaviour of the pellet injected particles was studied. The pellet penetration depth was changed by changing the electron temperature through scanning Ip and ne. The decay time of the electron density was increased with increasing the maximum penetration position of r/a.